home / Education/ Device for finding faults in circuits. Repair of TVs - a technique for finding faults

A device for finding faults in circuits. Repair of TVs - a technique for finding faults

Here I plan to describe practical techniques for troubleshooting electronics problems, as much as possible without being tied to specific hardware. The reasons for inoperability are considered to be the failure of an element, errors of developers, installers, etc. The methods are interconnected and almost always require complex application. Search is sometimes very closely related to elimination. In the process of working on the text, it became clear that the methods are very interrelated and often have similar features. Maybe you could say that the methods overlap each other. However, it was decided not to combine similar methods into one, in order to highlight problems from different angles and more fully describe the troubleshooting process.

Basic concepts of troubleshooting.

1. The action must not harm the device under test.

2. The action should lead to the predicted result: - hypothesis about the serviceability or malfunction of a block, element, etc. - confirmation or refutation of the hypothesis put forward and, as a consequence, localization of the malfunction;

3. It is necessary to distinguish between probable malfunction and confirmed (detected malfunction), put forward a hypothesis and a confirmed hypothesis.

4. It is necessary to adequately assess the maintainability of the product. For example, boards with elements in a BGA package have very low maintainability due to the impossibility or limited ability to apply basic diagnostic methods.

5. It is necessary to adequately assess the profitability and need for repairs. Often, repairs are not profitable in terms of costs, but they are necessary in terms of technology development, product study, or for some other reason.

Method description schema:

Method essence
Method capabilities
Advantages of the method
Disadvantages of the method
Application of the method

1. Clarification of the history of the occurrence of the malfunction.

The essence of the method: The history of the occurrence of a malfunction can tell a lot about the localization of the malfunction, which module is the source of the system inoperability, and which modules are out of order due to the initial malfunction, and the type of faulty element. Also, knowledge of the history of the occurrence of a malfunction can greatly reduce the testing time of the device, improve the quality of repair, and the reliability of the repaired equipment. Clarification of the history allows you to find out if the malfunction is the result of external influences, such as: climatic factors (temperature, humidity, dustiness, etc.), mechanical influences, pollution by various substances, etc.

Method capabilities: The method allows you to very quickly put forward a hypothesis about the localization of the fault.

Advantages of the method:

There is no need to know the intricacies of the product;
Super responsiveness;
No documentation required.

Disadvantages of the method:

The need to obtain information about events stretched out in time, in which you were not present, the inaccuracy and inaccuracy of the information provided;
Requires confirmation and clarification by other methods; in some cases, there is a high probability of error and inaccuracy of localization;

Application of the method:

If the malfunction at first appeared rarely, and then began to appear more and more often (within a week or several years), then, most likely, an electrolytic capacitor, an electronic lamp or a power semiconductor element is faulty, excessive heating of which leads to a deterioration in its characteristics.

If the malfunction appeared as a result of mechanical action, then it is likely that it will be possible to identify it by external inspection of the unit.

If a malfunction occurs with insignificant mechanical stress, then its localization should be started with the use of mechanical stress on individual elements.
If the malfunction appeared after any actions (modification, repair, revision, etc.) on the device, then you should pay special attention to the part of the product in which the actions were performed. You should check the correctness of these actions.
If a malfunction occurs after climatic influences, exposure to moisture, acids, vapors, electromagnetic interference, power surges, it is necessary to check the compliance of the performance characteristics of the product as a whole and its components with the operating conditions. If necessary, take appropriate measures. (change in working conditions or changes in the product, depending on the tasks and capabilities)
The manifestations of a malfunction at different stages of its development can tell a lot about the localization of a malfunction.

2. External examination.

The essence of the method: External examination is often neglected, but it is an external examination that allows localizing about 50% of faults, especially in small-scale production conditions. External examination in terms of production and repair has its own specifics.

Method capabilities:

The method allows detecting a malfunction in a super-operative manner and localizing it with an accuracy of an element in the presence of an external manifestation.

Advantages of the method:

Super responsiveness;
Exact localization;
A minimum of equipment is required;
No documentation required (or minimum availability).

Disadvantages of the method:

Allows you to identify only faults that appear in the appearance of the elements and parts of the product;
As a rule, requires disassembly of the product, its parts and blocks;
Requires the performer's experience and excellent vision.

Application of the method:

In production conditions, special attention must be paid to the quality of the installation. The quality of installation includes: the correct placement of elements on the board, the quality of the soldered connections, the integrity of the printed conductors, the absence of foreign inclusions in the board material, the absence of short circuits (sometimes short circuits are visible only under a microscope or at a certain angle), the integrity of the insulation on the wires, reliable fastening of the contacts in the connectors. Sometimes an unsuccessful construct provokes short circuits or breaks.
In the context of repair, you should find out if the device has ever worked correctly. If it did not work (case of a factory defect), then check the quality of the installation.
If the device worked normally, but failed (the case of actual repair), then you should pay attention to traces of thermal damage to electronic elements, printed conductors, wires, connectors, etc. Also, during inspection, it is necessary to check the integrity of the insulation on the wires, cracks from time cracks as a result of mechanical stress, especially in places where conductors work on kink (for example, sliders and flips of mobile phones). Particular attention should be paid to the presence of dirt, dust, leakage of electrolyte and odor (burning, mold, faeces, etc.). The presence of contaminants can be the reason for the inoperability of the electronic equipment or an indicator of the cause of the malfunction (for example, electrolyte leakage).
Inspection of printed wiring requires good lighting. The use of a magnifying glass is desirable. As a rule, shorts between solders and poor-quality solders are visible only from a certain angle of view and illumination.

Naturally, in all cases, you should pay attention to any mechanical damage to the case, electronic elements, boards, conductors, screens, etc.

3. Ringing.

The essence of the method: The essence of the method is that with the help of an ohmmeter, in one form or another, the presence of the necessary connections and the absence of unnecessary connections (closures) are checked.

Method capabilities:

Prevention of malfunctions in production, quality control of installation;
Testing the hypothesis about the presence of a fault in a specific circuit;

Advantages of the method:

simplicity;
high qualification of the performer is not required;
high reliability;
precise localization of the malfunction;

Disadvantages of the method:

high labor intensity;
restrictions when checking boards with mounted elements and connected harnesses, elements in the circuit.
the need to get direct access to contacts and items.

Application of the method:

In practice, as a rule, it is sufficient to check the presence of the necessary connections. The absence of short circuits is checked only in the power supply circuits.
The absence of unnecessary connections is also ensured by technological methods: marking and numbering of wires in a bundle.
A check for the presence of unnecessary connections is carried out in the case when there is a suspicion of specific conductors, or a suspicion of a design error.
It is extremely time-consuming to check for unnecessary links. In this regard, it is carried out as one of the final stages, when a possible short circuit (for example, there is no signal at the control point) is localized by other methods.
It is possible to very accurately localize the short circuit using a milliohmmeter, with an accuracy of several centimeters.
Although this technique has certain disadvantages, it is very widely used in small-scale production, due to its simplicity and efficiency.
It is better to call according to the dialing table, drawn up on the basis of the electrical circuit diagram. In this case, possible errors in the design documentation are corrected and the absence of errors in the dial itself is ensured.

4. Removal of performance characteristics

The essence of the method. When using this method, the product is switched on under operating conditions or under conditions that simulate workers. And they check the characteristics by comparing them with the necessary characteristics of a serviceable product or theoretically calculated. It is also possible to take characteristics of a separate block, module, element in a product.

Method capabilities:

Allows you to quickly diagnose the product as a whole or a separate unit;
Lets approximately estimate the location of the malfunction, identify a functional block that is not working correctly, in case the product does not work correctly;

Advantages of the method:

Sufficiently high efficiency;
Accuracy, adequacy;
Assessment of the product as a whole;

Disadvantages of the method:

The need for specialized equipment or, at least, the need to assemble a wiring diagram;
The need for standard equipment;
The need for a sufficiently high qualification of the performer;
It is necessary to know the principles of operation of the device, the composition of the device, its block diagram (to localize the malfunction).

Application of the method: For example:

In the TV, they check the presence of an image and its parameters, the presence of sound and its parameters, power consumption, heat dissipation. By the deviation of certain parameters, the serviceability of the functional blocks is judged.
In a mobile phone on a tester, the parameters of the RF path are checked and, by the deviation of certain parameters, they judge the health of the functional blocks.
Naturally, you need to be sure that all external units are in good working order and that the input signals are correct. For this, the operation of the product (element, block) is compared with the operation of a serviceable one under the same conditions and in this switching scheme. This does not mean theoretically the same scheme, but practically the same "hardware". Or you need to compare all the input signals.

5. Observation of the passage of signals through the cascades.

The essence of the method: With the help of measuring equipment (oscilloscope, tester, spectrum analyzer, etc.), the correct propagation of signals along the stages and circuits of the device is observed. To do this, measure the characteristics of the signals at the control points.

Method capabilities:

assessment of the performance of the product as a whole;
performance assessment for cascades and functional blocks;

Advantages of the method:

high accuracy of fault localization;
the adequacy of the assessment of the state of the product as a whole and in cascades;

Disadvantages of the method:

great difficulty in evaluating circuits with feedback;
the need for high qualifications of the performer;
labor intensity;
ambiguity of the result when used incorrectly;

Application of the method:

In circuits with a sequential arrangement of cascades, the disappearance of the correct signal at one of the control points indicates a possible malfunction of either the output, or a short circuit at the input, or a communication failure.
First, they isolate the built-in signal sources (clock generators, sensors, power modules, etc.) and sequentially find the node in which the signal does not correspond to the correct one described in the documentation or determined using simulation.
After checking the correct functioning of the built-in signal sources, test signals are applied to the input (or inputs) and again the correctness of their propagation and conversion is checked. In some cases, for a more efficient application of the method, a temporary modification of the circuit is required, i.e. if necessary and possible - breaking the feedback circuits, breaking the communication circuits of the input and output of suspected cascades

Fig. 1 Temporary modification of the device to eliminate the ambiguity of finding the malfunction. The crosses indicate the temporary break of the bonds.

In feedback loops, it is very difficult to get unambiguous results.

6.Comparison with a good unit.

The essence of the method: It consists in comparing various characteristics of a known good product and a faulty one. By the differences in appearance, electrical signals, electrical resistance, the localization of the malfunction is judged. Method capabilities:

Rapid diagnostics in combination with other methods;
Possibility of repair without documentation.

Advantages of the method:

Operational troubleshooting;
There is no need to use the documentation;
Eliminates modeling and documentation errors;

Disadvantages of the method:

The need for a serviceable product;
The need for combination with other methods

Application of the method: Comparison with a healthy unit is a very effective method because not all product characteristics and signals are documented in all circuit nodes. It is necessary to start the comparison with a comparison of the appearance, the location of the elements and the configuration of the conductors on the board, the difference in the installation indicates that the design of the product has been changed and, most likely, a mistake has been made. The various electrical characteristics are then compared. To compare the electrical characteristics, they look at the signals at different points of the circuit, the operation of the device in different conditions, depending on the nature of the manifestation of the malfunction. It is quite effective to measure the electrical resistance between different points (boundary scan method).

7. Modeling.

The essence of the method: The behavior of a serviceable and faulty device is simulated and, on the basis of the simulation, a hypothesis is put forward about a possible malfunction, and then the hypothesis is tested by measurements. The method is used in combination with other methods to increase their effectiveness.

Method capabilities:

Prompt and adequate hypothesis on the location of the fault;
Preliminary testing of the hypothesis about the location of the fault.

Advantages of the method:

Ability to work with disappearing faults,
Adequacy of the assessment.

Disadvantages of the method:

high qualification of the performer is required,
a combination with other methods is required

Application of the method: When eliminating a periodically manifested malfunction, it is necessary to apply simulation to find out whether the replaced element could provoke this malfunction. For modeling, it is necessary to understand the principles of equipment operation and sometimes even know the subtleties of work.

8.Division into functional blocks.

The essence of the method: For preliminary fault localization, it is very effective to divide the device into functional blocks. It should be borne in mind that often the structural division into blocks is not effective from the point of view of diagnostics, since one structural block can contain several functional blocks or one functional block can be structurally made in the form of several modules. On the other hand, the structural block is much easier to replace, which makes it possible to determine which structural block the fault is in.

Method capabilities:

Allows you to optimize the use of other methods;
Allows you to quickly determine the location of the fault;
Allows you to deal with complex faults

Advantages of the method:

Speeds up the troubleshooting process;

Disadvantages of the method:

A deep knowledge of the circuitry of the product is required;
It takes time to thoroughly analyze the device

Application of the method: There are two options:

If the product consists of blocks (modules, boards) and their quick replacement is possible, then, by changing the blocks in turn, they find the one, when replaced, the malfunction disappears;
In another version, analyzing the documentation, they make up a functional diagram of the device, based on the functional diagram, they simulate (as a rule, mentally) the operation of the product and put forward a hypothesis about the location of the malfunction.

9. Temporary modification of the circuit.

The essence of the method: To eliminate mutual influence and to eliminate ambiguity in measurements, sometimes it is necessary to change the product diagram: to break off connections, connect additional connections, to solder or solder elements.

Method capabilities:

Fault localization in circuits with OS;
Exact localization of the malfunction;
Elimination of the mutual influence of elements and circuits.

Advantages of the method:

Allows you to clarify the location of the fault.

Disadvantages of the method:

The need to modify the system
The need to know the intricacies of the device

Application of the method: Partial disconnection of circuits applies in the following cases:

when the circuits interfere and it is not clear which one is the cause of the malfunction;
when a faulty unit can damage other units;
when there is an assumption that an incorrect / faulty circuit blocks the operation of the system.

Use extreme caution when disconnecting protection circuits and negative feedback circuits. turning them off can result in significant damage to the product. Disconnection of the feedback circuits can lead to a complete disruption of the operation mode of the cascades and, as a result, not give the desired result. Opening the PIC circuit in the generators naturally leads to a breakdown in generation, but it can make it possible to remove the characteristics of the cascades.

10. Inclusion of the functional block outside the system, in conditions that simulate the system.

The essence of the method: In essence, the method is a combination of methods: Partitioning into functional blocks and Removal of external performance characteristics. When a malfunction is detected, the "suspect" unit is checked outside the system, which allows either to narrow the search circle if the unit is working properly, or to localize the malfunction within the unit if the unit is defective.

Method capabilities:

testing the hypothesis about the performance of a particular part of the system

Advantages of the method:

the possibility of testing and repairing a functional unit without the presence of a system.

Disadvantages of the method:

the need to collect the verification scheme.

Application of the method: When using this method, it is necessary to monitor the correctness of the conditions created and the tests used. Blocks can be poorly coordinated with each other during the development phase.

11.Preliminary check of functional blocks.

The essence of the method: The functional block is pre-checked outside the system, on a specially made stand (workstation). When repairing, this method makes sense if the block does not require too many input signals or, in other words, it is not too difficult to simulate the system. For example, this method makes sense to use when repairing power supplies. Method capabilities:

Testing the hypothesis about the unit's performance;
Prevention of possible malfunctions when assembling large systems.

Advantages of the method:

The ability to check the main characteristics of the unit without interfering influences;
The ability to pre-check blocks.

Disadvantages of the method:

The need to collect a verification scheme

Application of the method: It is very widely used for the prevention of system malfunctions in the production of new products.

12. Replacement method.

The essence of the method: The suspect unit / component is replaced with a known good one and the system is checked for proper functioning. Based on the test results, the correctness of the hypothesis regarding the malfunction is judged.

Method capabilities:

Testing the hypothesis about serviceability or failure of a block or element.

Advantages of the method:

Efficiency.

Disadvantages of the method:

The need for a replacement unit.

Application of the method: Several cases are possible: when the behavior of the system has not changed, this means that the hypothesis is incorrect; when all faults in the system are eliminated, then. the fault is really localized in the replaced unit; when some of the defects have disappeared, this may mean that only the secondary malfunction has been eliminated and the working unit will burn out again under the influence of the primary defect in the system. In this case, it may be best to re-install the replaced unit (if possible and appropriate) and continue troubleshooting with that. to eliminate exactly the root cause. For example, a failure in a power supply unit can lead to unsatisfactory operation of several units, one of which will fail as a result of overvoltage.

13. Checking the operating mode of the element.

The essence of the method: Compare the values of currents and voltages in the circuit with the presumably correct ones. They can be found in the documentation, calculated during simulation, measured when examining a healthy block. Based on this, a conclusion is made about the serviceability of the element.

Method capabilities:

Localization of a malfunction up to an element.

Advantages of the method:

Accuracy

Disadvantages of the method:

Slowness
High qualification of the performer is required;

Application of the method:

Check the correctness of the logic levels of digital circuits (compliance with standards, and also compare with the usual, typical levels);
check the voltage drops on diodes, resistors (compare with the calculated one or with the values in a working unit);
Measure the voltages and currents at the test points.

14. Provocative impact.

The essence of the method: Increase or decrease in temperature, humidity, mechanical stress. The use of such actions is very effective for detecting missing faults.

Method capabilities:

Detection of missing faults.

Advantages of the method:

A straw for a drowning man. :-)
In some cases, it is sufficient to operate with your hands or a screwdriver.

Disadvantages of the method:

Special equipment is often required.

Application of the method: As a rule, one should start by tapping on the elements. Try to touch the elements and harnesses. Heat the board under the lamp. In more complex cases, special cooling methods or climatic chambers are used.

15. Checking the temperature of the element.

Method essence is simple, with any measuring device (or finger) you need to evaluate the temperature of the element, or draw a conclusion about the temperature of the element by indirect signs (discoloration, burning smell, etc.). Based on these data, a conclusion is made about a possible malfunction of the element.

Application of the method: In general, everything is simple and clear, the complexity arises when assessing high-voltage circuits. And it is not always clear whether the element is in normal mode or overheating. In this case, it is necessary to compare with a serviceable product.

16. Execution of test programs.

The essence of the method: A test program is executed on a running system that interacts with various components of the system and provides information about their response, either the system under the control of the test program controls peripheral devices and the operator observes the response of peripheral devices, or the test program allows observing the response of peripheral devices to a test stimulus (pressing keys, reaction of the temperature sensor to temperature changes, etc.).

Advantages of the method: The advantages of the method include a very quick assessment according to the criterion works - does not work.

Disadvantages of the method: The method has significant drawbacks, since for the execution of the test program, the system kernel must be in good condition, an incorrect response does not allow to accurately localize the malfunction (both the periphery and the system kernel and the test program can be faulty).

Application of the method: The method is applicable only for final testing and elimination of very minor flaws.

17. Step-by-step execution of commands.

The essence of the method: Using special equipment, the microprocessor system is transferred to the mode of continuous (step-by-step) execution of instructions (machine codes). At each step, the condition of the buses (data, addresses, control, etc.) is checked and, comparing with the model or with a working system, conclusions are drawn about the operation of the device nodes. This method can be classified as one of the varieties of the "test program execution method", but the application of the method is possible on an almost inoperative system.

Advantages of the method:

Debugging of an almost non-working system is possible;

Low cost of the required equipment.

Disadvantages of the method:

Very high labor intensity.

Application of the method: The method is very effective for debugging microprocessor systems at the development stage.

18. Test signatures.

The essence of the method: With the help of special equipment, the state of the buses of the microprocessor device is determined in normal operation at each step of the program (or test program). We can say that this is a variant of the step-by-step execution of programs, only faster (due to the use of special equipment).

Advantages of the method:

Debugging of an almost non-working system is possible

Disadvantages of the method:

Great labor intensity.

Highly qualified performer.

Application of the method: The method is very effective for debugging microprocessor systems at the development stage.

19. "Exit to the entrance".

The essence of the method: If the product / system has an output (multiple outputs) and has an input (multiple inputs) and the input / output can operate in full duplex mode, then it is possible to check the system in which the signal from the output through external connections is fed to the input. The presence / absence of a signal, its quality is analyzed, and based on the results, an assessment is made on the performance of the corresponding circuits.

Advantages of the method:

Very high rate of performance assessment

Minimum additional equipment

Disadvantages of the method:

Limited use

Application of the method:

It is used for the final check of control systems. Maybe somewhere else.

20. Typical malfunctions.

The essence of the method: Based on past experience in repairing a specific product, a list of the manifestation of the malfunction and the corresponding defective item is compiled. The method is based on the fact that mass products have weaknesses, flaws, which, as a rule, lead to the failure of products. Also, this method should include the assumption that one or another element fails on the basis of reliability indicators.

Advantages of the method:

High speed

Not too high qualification of the performer

Disadvantages of the method:

Not applicable in the absence of fault statistics;

Requires confirmation of the hypothesis by other methods.

Application of the method: Most specialists keep statistics and symptoms of malfunctions in their heads. I have met attempts at a systematic presentation in the "Service manuals" (in the repair documentation) of the Nokia company.

21. Analysis of the impact of the malfunction.

The essence of the method: Based on the available information about the manifestation of the malfunction and the premise that all manifestations are caused by one malfunction, an analysis of the device is carried out. In this analysis, a "tree" of mutual influences of blocks (elements) is built and a block (element) is found, the failure of which could cause all (most) manifestations. If there is no solution, additional information is collected.

Advantages and disadvantages: As information is collected and received, it must be constantly analyzed from the point of view of this method. The method is as necessary as air. Without it - nowhere.

Application of the method: For example, the simplest case is that the device does not turn on at all. No heating, no extraneous sounds, no burning smell. When putting forward a hypothesis, it is necessary to assume the minimum cause and the minimum harm - this is a blown fuse. Checking the fuse. If the fuse is working properly, we continue to collect information. The key principle is the assumption about minimality of the reason.

22. Peripheral scanning.

The essence of the method: Measure the resistance between test points. It differs from dialing in that we are interested in the value of resistance, and not only in the presence or absence of communication. The term "Checkpoint" is used in a broad sense. Control points can be selected by the performer himself.

Advantages of the method:

Possibility of automated control according to the criterion "good - not good"

Possibility of in-circuit check of elements

Disadvantages of the method:

Requires a sample or database of resistances in a healthy unit

It is difficult to make a theoretical assumption about the correct value of resistance, especially if the circuit is complex and ramified.

Application of the method: To measure resistance, it is necessary to use equipment that excludes the failure of the device as a result of measurements. It can be used as a tester in repair conditions, as well as automatic machines as part of a large production line.

3.1.1. Features of a typical PC power supply circuit. The main criteria for diagnosing power supplies.

Main functional units

To understand the functioning and structure of the power supply of the system module, below are the structural diagrams of typical AT / ATX sources and the operation of the most complex unit of the structural diagram, the half-bridge converter, is explained. Structural schemes AT, ATX power supplies are shown in Figures 1.2 and 1.3.

Structural diagrams of AT / ATX power supplies AT format power supply

In the AT format power supply (Figure 1.2), the supply voltage through external the circuit breaker located in the case of the system unit goes to network filter and low frequency rectifier. Further, the rectified voltage, of the order of 300V, is converted into a pulsed one by a half-bridge converter.

Interchange between the primary network and consumers pulse transformer. The secondary windings of the pulse transformer are connected to high-frequency rectifiers + 12V and ± 5V and corresponding smoothing filters.

Power Good signal(power supply is normal), supplied to the system board in 0.1 ... 0.5 after the appearance of supply voltages of +5 V, performs initial processor setup. Failure of the power section of the source is prevented by the protection and blocking unit. In the absence of emergency modes, these circuits generate signals that enable the operation of the PWM controller, which controls the half-bridge converter by means of a matching stage. In emergency modes, the P.G. signal is reset.

Maintaining the output voltages at a constant value in the controller is provided by a closed-loop control system, while the deviation of the output voltage from the +5 V and + 12V source is used as an error.

Figure 18 - Block diagram of the ATX format power supply

ATX format power supplies
The ATX power supply (Figure 17) is distinguished by the presence of:

auxiliary converter;
standby source rectifier +5 BSB;
additional source +3.3 V;
control devices for remote switching on of the power supply by the PS_ON signal that controls the operation of the PWM controller.

Functional elements

The section discusses examples of the practical implementation of the elements of structural diagrams of power supplies, as well as reference data of the main elements of the circuits and their analogs.

Input filter

In order to prevent the penetration of impulse noise generated by the power source into the electrical network, a suppression filter is usually switched on at its input.

In addition to suppressing interference, the filter, as an input element, also performs a protective function in emergency modes of operation of the power supply - current protection, overvoltage protection.

In some power supply circuits, a non-linear element is included in the filter. varistor, designed to limit the charging current of a high-voltage capacitive filter. In this clause, we will consider only those measures that are used to protect against noise at the input of the power supply.

Typical blocking filter layout

Typical diagram of a system module power supply suppression filter (Figure 18). Capacitor C1 is switched on at the filter input, then the AC power supply voltage is supplied to the power supply of the system module through a network inductive-capacitive filter.

Current protection is carried out by fuse F1, which limits the load current to no more than 1.25 of the nominal value, and from overvoltage in the network (overvoltage) is carried out by varistor Z1. When the voltage of the supply network rises above a certain level, the resistance of the element Z1 sharply decreases, causing the fuse to operate.

Figure 19 - Diagram of a suppression filter

Low frequency rectifier

The power supply of the converters is carried out with a constant voltage, which is generated low frequency rectifier(Figure 19 ). The rectification bridge circuit, made on diodes D1 ... D4, ensures proper rectification of the mains voltage. The subsequent smoothing of the rectified voltage ripple is carried out by a filter on the choke L1 and the series-connected capacitors CI, C2. Resistors Rl, R2 create a discharge circuit for capacitors CI, C2 after disconnecting the power supply from the network.

The possibility of supplying from the 115 V network is realized by introducing a switch for selecting the supply voltage into the rectifier circuit. The closed state of the switch corresponds to a low supply voltage (-115 V). In this case, the rectifier works according to the voltage doubling circuit, and the charging process will proceed as follows. Let at some point in time at the input of the rectifier positive

half-cycle of the mains voltage. This is equivalent to an external source with positive terminal 1 and negative terminal 2. The capacitor C1 will be charged along the circuit:
+ Ucem(terminal 1) →D2 → L1 → C1 →SW1→ NTCR1 → - (terminal 2).

When the polarity of the half-cycle of the input voltage changes, the capacitor C2 will be charged along the circuit:
+ Ucem(terminal 2) →NTCR1 → SW1 → C2 →D1→ -Ucem(terminal 1).

The output voltage corresponds to the sum of the voltage across the capacitors C1, C2.

One of the functions of the rectifier is to limit the charging current of the input capacitor of the low-pass filter, performed by the elements that make up the rectifier device of the power supply. The need for their use is due to the fact that the start mode of the converter is close to the short circuit mode. The charging current of a capacitor when connected directly to the network can be significant and reach several tens to hundreds of amperes.

The use of NTCR1 thermistors with negative TCS (Figure 19), connected in series in the capacitor charging circuit, eliminates the unwanted effects of charging the input capacitor of the low-pass filter. The thermistor has some resistance in the "cold" state, after passing the peak of the charging current, the resistor heats up and its resistance becomes 20 ... 50 times less. Varistors Zl, Z2 are used in high quality power supplies. Their use is explained by the need to protect the unit from overvoltage in the supply network.

Figure 20 - Diagram of a low-frequency rectifier and the principle of operation of the voltage switch (a, b)

Half-bridge high frequency converter

In the power supplies of the system modules, the high-frequency converter is made according to the scheme of a half-bridge push-pull voltage converter, the schematic diagram of which is shown in Figure 1.4. The active elements of the circuit are transistor switches Q1, Q2 with reverse-connected diodes Dl, D2. Using capacitors CI, C2, the diagram shows the capacitances of collector-emitter junctions of transistors, mounting diodes, transformer T1, etc., and from capacitors C4, C5, a voltage divider of the primary source EpIT is formed. Elements D3, D4, Lf, Cf form an output rectifier.

The shape of the voltages in the collector Q2 (emitter Q1) is determined by the processes of energy storage in the primary winding of the transformer T1, the leakage inductance L $ and the charge (discharge) of the capacitors CI, C2. If the transistor Q1 is open, the capacitor C1 is discharged through the open junction to-e of the transistor Q1 and the capacitor C2 is charged, causing a voltage surge in the collector Q2 together with the action of the inductance L$. V In the case of an open transistor Q2, capacitor C2 is discharged and C1 is charged, while in the emitter of Q1 there is a voltage surge due to the charge of this capacitor. On the timing diagrams (Figure 1.5), there is an increase in the charge current of the capacitors C1 (C2), which is explained by the increase in the magnetizing current T1. Capacitors C4, C5 in this circuit are reactive equivalents of bridge transistors and close the circuit of current flow through the primary winding T1.1.

Timing diagrams of voltages and currents

Transistor switches Ql, Q2 open and close in antiphase with signals U1 and U2 (see Figure 1.5), time t0-t2 corresponds to the open state of transistor Q1. In this case, the primary winding of the transformer T1.1 turns out to be connected to the output of the capacitive voltage divider C4, C5, as a result of which the voltage across the locked transistors does not exceed the value of Epit / 2.

Figure 21 - Schematic diagram of a push-pull half-bridge voltage converter

Push-pull circuits are characterized by the phenomenon of "through currents", the cause of which is the inertia of the transition of the transistor from the on state to the off state due to the finite time for the absorption of excess minority carriers. The way to deal with through currents is to create a fixed delay of the opening signal in relation to the closing signal.

Auxiliary converter

Auxiliary converter is a design feature of ATX format power supplies. This converter generates + 5BSB voltage when the system module is off. The device is a blocking generator operating in a self-oscillating mode during the entire time of the closed state of the mains switch of the power supply.

Simplified diagram self-oscillating blocking generator for the flyback converter is shown in Figure 21. The main elements of the blocking generator are transistor Q and transformer T1. The positive feedback loop is formed by the secondary winding of the transformer, capacitor C and resistor R, which limits the base current. Resistor R$ creates a capacitor discharge circuit at the stage of the closed state of the transistor. Diode D eliminates the negative polarity voltage pulse that occurs when the transistor is turned off into the load RH. The branch, consisting of diode D1, resistor R1 and capacitor C1, performs the function of protecting the transistor from overvoltage in the collector circuit.

Figure 22 - Schematic diagram of a self-oscillating blocking generator
Figure 23 - Timing diagrams of work Figure 24 - Schematic of the auxiliary converter

A diagram of a typical autogenerator type converter is shown in Figure 23. In all converter circuits, the switch transistor operates in a mode with large commutation overloads in the collector current, therefore a powerful transistor is used in the autogenerator. To increase the duration of the "pause" of the key transistor in the self-oscillating mode, an additional source of negative bias is used. The limitation of the control signal emissions is carried out by the Zener diode ZD2, which is connected to the base circuit of the key transistor Q3. In the damping circuit, it is permissible to use an RC circuit included in the collector circuit of the transistor; in some cases, a damping RC circuit is also installed in the key base circuit.

Output rectifier

The output rectifiers of the power supply are distinguished by the voltage value of the output channel. They are made according to a push-pull scheme and, as already noted, are available on UBbIX = +12 V, +5 V, -12 V and -5 V. Due to the high frequency of the converter, the use of special elements that allow operation at increased frequencies and temperatures is explained. So, as rectifiers, Schottky diodes are used, which have a low voltage drop in the forward direction (0.2 ... 0.3 V for silicon diodes), and low-loss capacitors that allow operation at high temperatures.

The diagram of the output rectifier of a typical ATX power supply is shown in Figure 24. The rectifier of each channel is made according to a full-wave rectifier circuit, which has a lower ripple factor than a half-wave one. The filtering of the output voltage of the output voltages is carried out by inductive (LI, L3, L4) and capacitive filters (C19, C20, C21, C22 and C25). The inclusion of serial RC-circuits R9, CU and R10, SP parallel to the windings of the transformers allows to reduce the intensity of noise generated by the source. The possibility of a significant increase in voltage at the output of the rectifier when the load is off is eliminated by resistors R31, R32, R33, R34.

The rectifier +3.3 V of power supplies of ATX format (Figure 3.40) can be executed according to the scheme of the simplest serial compensation voltage stabilizer, such as in PM-230W.

Figure 25 - Diagram of the output rectifier of a typical ATX power supply

Signal conditionersPowerGood

For the correct start of the computer system in the motherboard, a power supply delay is organized for a time until the transient processes in the power supply are over and the output voltage is set to the nominal values. For this purpose, a special signal is generated in the power supply. PowerGood("Food is normal"). The Power Good signal delayed for 0.1 ... 0.5 s is a logic-one level, of the order of +5 V, which is intended for the initial installation of the motherboard.

Shapers can be made in discrete and integral design.

Figure 26 - Scheme of the PG signal generator

LM339; KA339 (four comparators in one housing);
LM393; KA393 (two in one case) or in the form of a specialized microcircuit М51975А.

Protection and control circuits

Protection of power supplies manifests itself in critical modes of operation, as well as in those cases when the feedback action can lead to the limiting modes of operation of circuit elements, thereby preventing the failure of power and expensive circuit elements.

As a result of the action of the protection circuits, the output control signals from the PWM controller are removed, the transistors of the converter are in the off state, and there is no output secondary voltage. A distinction should be made between the following protection circuits:

from short circuit in the load;
from excessive current in the transistors of the half-bridge converter;
overvoltage protection.

The first two types of protection are close in action and are associated with preventing the transfer of high power by the converter to the load. They act in case of overloading of the power supply or malfunctions in the converter. Overvoltage protection can occur during input voltage surges and in some other cases.

Turning off the converter in power supplies is carried out using an additional error amplifier, usually an error amplifier 2, turned on by a comparator or via a pause control channel. Below is a description of the protection circuits of the considered power supplies.

Figure 27 - Scheme of protection and control circuits

Figure 28 - Block diagram of the ms PWM controller

3.1.2. Malfunctions of power supplies, their symptoms, causes and remedies

The power supply is a complex electronic device, the repair of which must be carried out, accurately representing its work and having the skills to find and eliminate defects. When repairing, it is recommended to use all available troubleshooting methods in a comprehensive manner.

It must be remembered that the connection to the power supply network should only take place through an isolation transformer.

Repairs should be carried out with technically sound devices, using low-voltage soldering irons.

Group stabilization of UPS output voltages is characterized by the fact that with an increase in the load current of one of the secondary rectifiers, the load of the pulse transformer increases, and this affects the values of the output voltages of all rectifiers connected to it. Therefore, when repairing a power supply unit, an equivalent load should be used.

For a 200 W power supply, use equivalent loads: for a +5 V power supply, a 4.7 ohm load (50 W), for a +12 V power supply, a 12 ohm load (12 W).

Problems that can occur when a power supply fails can be classified as obvious and non-obvious.

TO obvious include: the computer does not work at all, the appearance of smoke, the fuse on the switchboard burns out.

Unobvious in order to eliminate errors in determining a faulty element, additional diagnostics of the system are required, however, they can be associated with the operability of the source:

any errors and freezes when turning on the power;
spontaneous reboot and periodic freezes during normal operation;
chaotic parity errors and other memory errors;
simultaneous stopping of the hard disk and the fan (no + 12V), overheating of the computer due to the failure of the fan;
restarting the computer at the slightest decrease in the mains voltage;
electric shock when touching the computer case or connectors
small static discharges that disrupt the network.

Pay special attention to the "Power OK" signal conditioning circuit, early application of this signal can lead to distortion of the CMOS memory.
When repairing the UPS, the following methods should be used:

Installation analysis method

This method allows, using the human senses (sight, hearing, touch, smell), to find the location of the defect with the following signs;

burnt radioelement, poor-quality soldering, a crack in the printed conductor, smoke. sparking, etc .;
various sound effects (squeak, "poke", etc.). the source of which is the UPS pulse transformer;
overheating of radioelements;
the smell of burnt radioelements

Measurement method

The method is based on the use of measuring instruments when searching for defects, a voltmeter, an ohmmeter, an oscilloscope.

Replacement method
The method is based on replacing a dubious radio element with a known good one.

Exclusion method

The method is based on temporary disconnection (in case of possible leakage or breakdown) or jumpering of terminals (in case of possible breakage) of doubtful elements.

Method of exposure

The method is based on analyzing the reaction of the circuit to various manipulations performed by a technician:

changing the positions of the sliders of the setting variable resistors (if any);
jumpering the terminals of transistors in DC circuits (emitter with base, emitter with collector);
change in the supply voltage (with oscilloscope control of the PWM circuit operation);
bringing the tip of a hot soldering iron to the body of a dubious radioelement and other manipulations.

Electro run method

Allows you to find recurring defects and check the quality of the repair performed (in the latter case, the run should be at least 4 hours).

Knocking method

The method allows you to detect installation defects on a switched-on power supply unit by swinging the elements, twitching the conductors, tapping on the chassis with a rubber mallet, etc.

Equivalents method

The method is based on temporarily disconnecting a part of the circuit and replacing it with a set of elements that have the same effect on it. Similar sections of the circuit can be pulse generators, auxiliary sources of constant voltage, load equivalents

At the same time, any specific characteristics of the unit, obtained from the documentation for it, or read from its body, can and should be used during its repair.

When troubleshooting a malfunction, the technician must not only apply these methods in their pure form, but also combine them.

Typical malfunctions of the PC power supply
Typical reasons for the occurrence of emergency modes in the UPS circuit are:

"surges" of the mains voltage, causing an increase in the amplitude of the pulse on the collector of the key transistor:
short circuit in the load circuit
an avalanche-like increase in the collector current due to saturation of the magnetic circuit of the pulse transformer, for example, due to a change in the magnetization characteristic of the magnetic circuit during overheating or an accidental increase in the duration of the pulse that opens the transistor.

ONE OF THE MOST CHARACTERISTIC FAULTS is a "breakdown"

rectifier bridge diodes or powerful key transistors, leading to a short circuit in the primary circuit of the UPS. A breakdown of the rectifier bridge diodes can lead to a situation where the alternating mains voltage will directly fall on the electrolytic smoothing capacities of the mains filter. In this case, the electrolytic capacitors at the output of the rectifier bridge explode

A short circuit in the primary circuit of a UPS can occur mainly for two reasons.

due to a change in the parameters of the elements of the basic circuits of powerful key transistors (for example, as a result of aging, temperature exposure, etc.):
due to the connection of a computer to an outlet: installed in a network, loaded, in addition to computer equipment, by high-current installations (machine tools, welding machines, dryers, etc.)

As a result, impulse noise with an amplitude of up to 1 kV can occur in the network. which lead, as a rule, to a "breakdown" in the collector-emitter section of powerful key transistors.

The third reason for a short circuit in the primary circuit of the UPS is the ignorance of the maintenance personnel who take measurements with a grounded oscilloscope in the primary circuit of the UPS!

With a short circuit in the primary circuit of the UPS, the current-limiting thermistor with a negative TCR burns out (with an explosion). This happens after replacing a blown fuse and reconnecting to the network, if the main cause of the short circuit has not been eliminated. Since it is sometimes difficult to get these resistors, specialists who are repairing a power supply unit sometimes simply install a short-circuit jumper in the place where the thermistor should be. Thus, the current protection of the rectifier bridge diodes is removed, and the power supply unit will very soon fail again.

When replacing high-power key transistors, it is best to use transistors of the same type and from the same manufacturer. Otherwise, the installation of transistors of a different type can lead either to their failure, or to the failure of the UPS starting circuit (in the case of using more powerful transistors than were previously in the circuit)

SECOND CHARACTERISTIC FAILURE OF THE UPS is a failure of the TL494 control microcircuit. The operability of the microcircuit can be established by evaluating the operation of its individual functional units (without soldering from the UPS circuit). For this, the following technique can be recommended:

Operation 1.Checking DA6 generator and DA5 reference source

The serviceability of the DA6 generator is assessed by the presence of a sawtooth voltage with an amplitude of 3.2V at pin 5 of the microcircuit (provided that the frequency setting capacitor and resistor connected to pins 5 and 6 of the microcircuit are in good condition, respectively).

The serviceability of the DA5 reference source is assessed by the presence of a + 5V constant voltage at pin 14 of the microcircuit, which should not change when the supply voltage at pin 12 changes from + 7V to + 40V.
Operation 2. Checking the health of the digital path.

Without connecting the UPS to the network, apply a supply voltage of 10-15V from a separate source to pin 12 of the control microcircuit

The serviceability of the digital path is assessed by the presence at pins 8 and 11 of the microcircuit (if the output transistors of the microcircuit are switched on according to the scheme with OE) or at pins 9 and 10 (if they are switched on according to the scheme with OK) of rectangular pulse trains at the moment of power supply.

Check for a phase shift between the output pulse trains, which should be half the period.

Operations 3 Serviceability check of the "dead zone" comparator DA1.

Without connecting the UPS to the network, apply a 10-15V supply voltage from a separate source to pin 12 of the control microcircuit.

Make sure that the output pulses disappear at pins 8 and 11 when pin 14 of the microcircuit is closed with pin 4

Operation 4 Checking the serviceability of the PWMDA2 comparator.

Not including the power supply unit in the network, apply a supply voltage of 10-15V from a separate source to pin 12 of the control microcircuit

Make sure the disappearance of the output pulses at pins 8 and 11 when you close pin 14 of the microcircuit with pin 3.

Step 5 Checking the serviceability of the error amplifier DA3.

Not including the power supply unit in the network, apply to pin 12 of the control microcircuit a supply voltage of 10-158 from a separate source.

Check the voltage level at pin 2, which should differ from zero. By changing the voltage at pin 1, supplied from a separate power source, in the range from 0.3V to 6V: check the voltage change at pin 3 of the microcircuit.

Step 6 Checking the DA4 error amplifier. Without connecting the UPS to the network, apply a supply voltage of 10-15V to pin 12 of the control microcircuit from a separate source.

Check the voltage level at pin 3. preliminarily setting the DA3 amplifier to the "hard 0" state at the output. To do this, the voltage at terminal 2 must exceed the voltage at terminal 1. Check the appearance of voltage at terminal 3 when the potential supplied to terminal 16 exceeds the potential applied to the terminal

THIRD CHARACTERISTIC MALFUNCTION is the way out of the rectifier diodes in the secondary circuits of the UPS (kz * as a rule, this is a breakdown or a decrease in the reverse resistance of the diode).

We draw your attention to the correct choice of a replaceable diode for current, switching frequency and reverse voltage "

In the + 5V generation channel, there are Schottky diodes. and in the remaining channels - ordinary silicon diodes.

It is necessary to provide a good heat sink for the rectifier diodes in the + 5V and + 12V channels.

When monitoring rectifier diodes, it is advisable to desolder them from the circuit, because as a rule, numerous elements are connected in parallel to them, and control of diodes without desoldering them from the circuit in this case becomes incorrect

It is also important that the power supply unit can generate all output voltages, and the PG signal will be equal to 0V and the processor will be blocked.

The PG signal generation circuit includes a lot of elements that can also fail.

The listed malfunctions are basic and. generally uncomplicated to find.

Sometimes failures that occur in the power supply circuit during the measurement process lead to emergency modes of operation of power transistors. Failures can be caused by an increase in the value of the mounting capacitance of the power supply circuit elements at the point where the measuring probes of the device are connected1

The mains fuse (3-5A) is always located on the circuit board of the power supply unit and practically protects the network from short circuits in the power supply unit, and not the power supply unit from overloads

Almost always, a blown mains fuse signals a power supply failure.

A kind of indicator of a running UPS can be the rotation of the fan, which is started with an output voltage of + 12V (or -12V).

However, to bring the PSU to the nominal mode and to correctly control all the output voltages of the PSU, an external load is required either on the motherboard or on resistances that provide the entire range of current loads indicated in Table 2. with a nominal value of about 0.5 Ohm and a dissipated power of at least 50W through the + 5V generation channel.

A healthy UPS should run silently. This follows from the fact that the conversion frequency is outside the upper threshold of the audible range. The only source of acoustic noise is a running fan.

If, in addition to the hum of the fan, a squeak, "ping" or other sounds are heard, then this clearly indicates that the UPS is malfunctioning or that it is in emergency mode! In this case, immediately turn off the UPS from the mains and rectify the fault.

For more complex cases of UPS failure, it is necessary to understand the principles of UPS operation. the causal relationship of individual nodes of the circuit and. of course, have a schematic diagram of this power supply

Typical power supply faults

Checking radioelements

A detailed check of radioelements can be carried out both with the help of digital multimeters and analog (pointer) ones. Consider checking typical power supply elements.

Diodes

Checking semiconductor diodes with a pointer device should be carried out by turning on the resistance measuring device, starting from the lowest limit (set the switch to the xl position). In this case, the resistance of the diode is measured in the forward and reverse directions. In the case of a working diode, the device will show a small resistance (several hundred ohms) for forward bias of the diode, in the reverse - an infinitely large resistance (rupture). For a faulty diode, the forward and reverse directions differ little.

When checking with a digital multimet, the device is transferred to the testing mode (otherwise, in the resistance measurement mode in the forward and reverse directions, the diode will show a gap). If the diode is operational, then the digital display shows the voltage of the pn junction, in the forward direction for silicon diodes this voltage is 0.5 ... 0.8 V, for germanium diodes 0.2 ... 0.4 V, in the opposite direction - gap.

Transistors

Considering that the transistor has two pn junctions, when testing transistors, both junctions are checked, otherwise the check is similar to checking diodes. The test is conveniently carried out by measuring the resistance of the junctions relative to the base terminal by placing one of the electrodes of the device to the base of the measured transistor. For low-power transistors, when measured with a pointer device, both transitions in the forward direction have fairly close values (of the order of hundreds of Ohms) and in the opposite direction there is a gap.

The collector-emitter junction, which must also have a gap, is additionally checked. When testing high-power transistors, the resistance of the transitions in the forward direction can be several ohms. The digital device shows the voltage for the forward direction of the transitions 0.45 ... 0.9 V.

To determine the structure and terminals of an unknown transistor, it is advisable to use a dial gauge. When determining the conclusions, you must first make sure that the transistor is working properly. To do this, the base output is determined by approximately the same small resistances of the base-emitter and base-collector transitions in the forward and large - in the opposite direction.

The polarity of the probe of the device, which displaces the transitions in the forward direction, will determine the structure of the transistor: if the probe of the device has polarity "-", then the transistor has a p-n-p structure, and if "+", then n-p-p. To determine the emitter and collector terminals of the transistor, the probes of the device are connected to the so far unknown terminals of the transistor. The found output of the base through a 1 kΩ resistor is alternately connected to each of the remaining terminals. In this case, the resistance of the collector-emitter junctions is measured in turn. The terminal to which the resistor is connected, having the lowest value of the junction resistance, will determine the collector of the transistor, the remaining electrode will be the emitter.

Optocouplers

To test the optocouplers, the input (light-emitting) part is supplied with voltage from an external power source. In this case, the resistance of the junction is controlled, as a rule, the collector-emitter in the receiving part. In a working optocoupler, the collector-emitter junction resistance is much lower when the power is on (several hundred ohms) than when it is off. A constant resistance of the collector-emitter junction indicates a malfunction of the optocoupler.

Capacitors

Defective capacitors can be identified during an external inspection of the defective power supply. Attention should be paid to cracks in the case, electrolyte leaks, corrosion at the terminals, heating of the capacitor case during operation. A good test can be a parallel connection of a known good capacitor to the tested one. The lack of such information indicates the need to desolder a suspicious capacitor. The device, included in the resistance measurement mode, is set to the upper limit. During testing, the ability of the capacitor to charge and recharge is checked. It is convenient to check with a pointer device. In the process of charging, the arrow of the device deviates to the zero mark, and then returns to its original state (infinite resistance). The larger the capacitance of the capacitor, the longer the charging process. In a "leaky" capacitor, the charging process continues with the discharge process, i.e. the subsequent process of reducing resistance. The digital multimeter beeps when testing capacitors. If there is no signal, the capacitor is defective.

Thermistors

In these resistors, the resistance changes significantly with temperature. Thermistors are checked at normal and elevated temperatures. An increased temperature can be achieved by heating the thermistor body, for example with a soldering iron. In power supplies, thermistors are usually used, the resistance of which at normal temperature is in units of Ohm, with a negative temperature coefficient of resistance, therefore, when heated, the resistance of a working thermistor should decrease.

3.1.3. Algorithms for finding malfunctions of the PC power supply

Before starting the repair of the PC power supply, the following measures must be taken:

Ensure the implementation of safety measures (connect the power supply unit through an isolation transformer);
Study, if available, the schematic diagram of the power supply unit, highlight the main structural blocks, get acquainted with the design features;
Determine the constructive placement of the main structural blocks of the power supply unit.
Draw up a plan (algorithm) for troubleshooting the power supply unit.

Figure 29 shows a general view of the power supply troubleshooting algorithm.

Figure 30-32 shows the search algorithms for the most common power supply failure cases.

Algorithms for troubleshooting in the PC power supply

Figure 29 - Algorithm for troubleshooting in the PC power supply

Figure 30 - Algorithm of troubleshooting in the PC power supply in cases where the output voltages do not differ from the nominal
Figure 31 - Algorithm of troubleshooting in the PC power supply, in the absence of some output voltages
Figure 32– Algorithm of troubleshooting in the PC power supply in cases of activation of the power supply protection and the absence of remote control of the power supply.

3.1.4. The main malfunctions of the motherboard, their symptoms, causes and remedies

4.1.4.1 Main elements of the motherboard

To create motherboards, a special set of microcircuits is usually used - a chipset. Usually it consists of two main parts: the south and north bridge (North Bridge, South Bridge), but it should be noted that now there are options made on the same microcircuit. The north bridge is usually used to organize communication between the processor and memory and AGP, while the south bridge is connected to the north bridge and serves as a peripheral (IDE, ISA, EEPROM, etc.).

The architecture of motherboards is most correctly (today) divided into two groups: using the PCI bus for communication between bridges, and using special interfaces. The use of PCI for communication between bridges is gradually being abandoned, and most new chipsets do not use this interface for communication with each other. This is primarily caused by the low PCI bandwidth: only 133Mb / s. Obviously, even 2 ATA100 channels will not be able to transfer data. It must be said that there are many differences between different types of chipsets, but most of them do not affect the overall structure. Below I give the structural diagrams of both options that are currently used.

Figure 33 - Block diagram of the motherboard

CPU - the main detail in the system, as you can see from the diagram, it is connected to almost all nodes of the board, except for MIO, and then on many old boards the gate signal GATE A20 was started from MIO.

VIP1 - the first secondary power supply, all processors starting from Pentium MMX have dual power supply. It should be noted that setting the supply voltage value is automatically supported by relatively new processors, and VID signals can be set with jumpers on the board, and not directly by the processor. Stabilizers are almost always impulse and special microcircuits are used for their implementation. They are powerful, and the output stages almost always have additional cooling.

VIP2 - the second secondary power supply is used to power all devices not powered by 5V. Despite the fact that the ATX power supply has a 3.3V power supply, many power circuits have additional stabilizers on the board.

In this block diagram, not all secondary power supplies are shown and are shown very conditionally, in real circuits everything is much more complicated. Any modern motherboard has at least 4 secondary power supplies: one for the memory - 3.3v / 2.5v, the second for AGP 3.3v / 1.5v, the third for 3.3v logic, the fourth for the processor core from 2.0v / 1.45v. The above scheme is valid only for outdated MBs, for example, I430TX.

CLOCK - reference generator, all devices on the motherboard are synchronized by one reference generator, the synchronization system is shown in the block diagram rather conventionally. In general, the following clock frequencies exist in a computer:

Host Bus Clock (CLK2IN) is the reference frequency (external processor bus frequency). It is from it that other frequencies can be obtained and it is it that is set by jumpers (jumpers);
CPU Clock (Core Speed) is the internal frequency of the processor at which its computational core operates. Can be the same as Host Bus Clock or obtained from it by multiplying by 1.5, 2, 2.5, 3, 4. Multiplication must be provided in the processor design.
ISA Bus Clock (ATCLK, BBUSCLK) is the clock frequency of the ISA system bus (SYSCLK signal). According to the standard, it should be close to 8 MHz, but in BIOS Setup it is possible to select it through the frequency division factor of the Host Bus Clock. Sometimes the computer remains operational even at an ISA bus frequency of about 20 MHz, but usually ISA expansion cards are designed for 8 MHz, and at high frequencies they stop working. Do not expect your computer to become twice as fast as this frequency is doubled. The DMA channels on the motherboard use another SCLK clock, which is typically half the ISA Bus Clock.
PCI Bus Clock is the clock frequency of the PCI system bus, which, according to the standard, should be 25 - 33.3 MHz. It is usually obtained by dividing the Host Bus Clock frequency by the desired factor. In computers, it is possible to increase it to 75 or even 83 MHz, but for reasons of reliability, it is recommended to adhere to the standard values.
VLB Bus Clock is the VLB local bus frequency, similar to PCI Bus Clock.

CLOCK BUFFER - the reference oscillator buffer is not used on all motherboards. On technical boards where the chipset controls memory synchronization, it is used to buffer synchronization signals, for example, it is used in motherboards based on VT82C694X.

MIO –Multi Input Output chip is a microcircuit of the input / output system. In fact, this is an external device, but unfortunately without this device (for example, in case of failure) the motherboard will not be able to turn on.

Includes:

Floppy Drive Controller - floppy disk controller, CMOS - energy-independent memory,

RTC –Real Time Clock Real time clock,

serial and parallel interface controller (COMA COMB LPT), keyboard controller

system for monitoring the state of the motherboard. In many chipsets, MIO is integrated into the south bridge partially or completely, for example VT82C686B.

NS. Ur . - level transducer, necessarily used for implementation. COM.MIO has a 5-volt interface, and a 12-volt COM port.

BIOS - Basic Input Output System - the main input / output system, usually implemented in the form of EEPROM - simply energy-independent memory, the volume usually ranges from 1 Mbit to 4 Mbit (128KB to 512KB). Serves to manage the system before loading the operating system. It is the program written in the BIOS that the machine executes when the system is turned on. If the integrity of the program recorded in the BIOS is violated, the system does not initialize. X-Bus or x-bus is a very loud term, just part of the signals for the BIOS, for example CE (Chip Enable - chip enable). Starts directly from the south bridge.

AGP –Accelerated Graphic Port –accelerated graphic port, a bus focused on the use of high-performance video adapters. The high transfer rate is provided by pipelining memory accesses. According to the specification, up to 256 memory access requests can be queued up !!!

RAM –Random Access Memory – random access memory, or simply memory.

PCI –Peripheral Component Interconnector – connector for connecting internal peripheral devices. Synchronous bus with a combined bus of address, data and commands, allowing to achieve data transfer rates up to 133MB / s or in PCI64 up to 266MB / s.

ISA –Industry Standard Architecture –Industry Standard Architecture, now an obsolete bus. Most modern chipsets do not support this bus.

USB –Universal Serial Bus –Universal serial bus. Now it has become widespread, has great prospects, now there is already a standard USB2.

IDE –Integrated Device Electronic –devices with an integrated controller. This bus is used to connect hard disk drives to CD-ROM and DVD-ROM drives.

HI - Hub Interface is an untranslatable play on words (Hub is a node or a center of something), when new fast peripheral devices began to appear, PCI began to fail to cope with their requests - 2 ATA100 - 200Mb / s - PCI –133Mb / s. This architecture was first applied in the I82810. In general, the concept of HI refers only to Intel chipsets from other manufacturers; similar interfaces have different names, although they perform the same functions and have probably similar protocols (unfortunately, there is no description of these protocols in the generally available documents). VIA has a similar protocol called V-Link interface.

FWHI - Firm Ware Hub Interface (Node interface for firmware - BIOS), after abandoning the ISA interface, the task arose of how to load the BIOS and was easily solved using the above interface. It should be noted that VIA chipsets do not have such an interface and the BIOS is loaded via the LPC interface.

Lpc –Low Pin Count Interface indeed the interface has only 7 pins: 4 for data and 3 for control. Used to connect MIO for Intel and for BIOS for VIA, SIS.

AC97 -standard interface for working with an external digital-to-analog or analog-to-digital converter, it is on its basis that built-in sound cards and cheap modems work.

3.1.4.2. System board malfunctions, their symptoms, causes and remedies

The main and most complex PC board is called the motherboard, the general system board (SP), since it contains the "heart" of the PC - the microprocessor. It also contains several very large integrated circuits (VLSI), RAM, ROM and a number of other microcircuits, switches - jumpers for PC operating modes, expansion connectors for connecting adapter and controller cards.

Diagnostics of malfunctions and repair of a joint venture is a difficult laborious, but, nevertheless, quite feasible and very interesting business.

JV malfunctions can also be subdivided into three main types:

Hardware;
Software;
software and hardware.

TO the first This type includes, for example, a broken contact in a multilayer printed circuit board or in one of the expansion connectors of the joint venture.

Loss of contact in the printed circuit board accounts for 50% of all joint venture faults. (Remember that power rails are usually mounted in the inner layers of the board.)

An example of "faults" second type can be overflow of RAM by resident programs, connection of a software driver incompatible with the connected peripheral device.

software and hardware malfunctions are failure of the BIOS ROM, loss or distortion of configuration information stored in non-volatile RAM (CMOS) on the SP,

Fault diagnosis is carried out in two ways:

Programmatically;
using instruments (oscilloscope, logic probe and analyzer).

Programmatic way is implemented using the built-in POST program, special diagnostic programs (Checkit, Norton Disk Doctor), as well as using diagnostic boards and the MB PAK.

A malfunction of the joint venture can be detected at the initial start of the PC (self-test, loading the operating system), when running programs and during operation (20 ... 30 minutes after switching on).

First of all, you should use the visual and audible alarms that are provided in the PC.

By the duration, number and alternation of sound signals (Table 1) generated by the computer as a result of self-diagnostics, it is possible to determine those subsystems that cause malfunctions. Of course, small POST tests are not capable of performing a complete check of the health of a computer, but this is the first barrier to a machine malfunctioning.

Table 1

Sound signal
1 short	Failure to update DRAM
2 short	Parity failure
3 short	Failure in the base RAM area 64 kb
4 short	System timer failure
5 short	Processor failure
6 short	Keyboard controller error
7 short	Virtual mode error
8 short	Memory test failed
9 short	ROM BIOS Checksum Failure
10 short	CMOS error
11 short	Cache error
1 long 3 short	Failure of main or extended memory
1 long 8 short	video test failed

If you have a working video card and monitor, then the PC, as a rule, additionally displays a digital error code on the screen.

There are hundreds of such codes, they are different for different types of BIOS, but by the first digit of the code (usually a three-digit one), you can determine which device has failed.

Codes 100 or higher indicate system board malfunction;
200 - RAM errors;

300 - keyboard errors; 400-500 - malfunctions of the display or printer; 600 - floppy disk drive errors;
700 - errors in the work of the math coprocessor;
900 - parallel printer testing errors;
1700 - errors in the hard disk circuits.

To facilitate the work at the first step of diagnostics, there is such a wonderful tool as a POST card.

The main function of these diagnostic cards is to record and display POST codes that are automatically generated by the POST procedure when checking the status of all computer subsystems when the power is turned on or the RESET button is pressed.

The use of a diagnostic board significantly increases the likelihood of correct fault localization. Most of the "hard-wired" diagnostic programs on the boards are written with the expectation that the microprocessor is working correctly.

This approach is quite justified, since the microprocessor very rarely fails. It should be noted that the presence of a listing with the source code of the BIOS in assembly language greatly increases the chances of solving your problems on your own.

If the BIOS ROM fails, the POST becomes problematic and no errors are displayed on the display.

To diagnose the second method, certain knowledge in the field of electronics and computer technology and skills in working with test equipment are required.

Methodology troubleshooting with instruments consists of
sequential verification:

correct installation of all switches of the system board operating modes and interface connectors;
system board supply voltages +5 V and +12 V;
supply voltages VIP MV
all crystal oscillators, clock generators and delay lines;
microprocessor operation (presence of standard signals at the outputs);
functioning of buses of addresses, data and control;
signals on contacts of ROM and RAM microcircuits;
signals on the contacts of the system board expansion connectors;
timing diagram of the VLSI set and low-integration circuits.

Ultra Large Integrated Circuits Fault Statistics

The most common causes of a joint venture malfunction are poor-quality PCB layout, low level of manufacturing technology and poor assembly. If in 1989-1990 it was mainly the buffer microcircuits and peripheral LSIs that were out of order, now the weakest link is the microcircuits from the VLSI set. The pace of development and implementation of new sets of VLSI for joint ventures has increased so much that products that are characterized by low reliability are sometimes put into production.

Local overheating of the joint venture has become quite common today, although the build quality is getting better.

3.1.5 Malfunctions of the power supply unit of the CPU, their symptoms and remedies

As a typical malfunction of the power supply circuit of the 5STX board, one can note the failure of the U11 PWM controller microcircuit - HIP6008CB. In this case, the board does not start; a closer look reveals the absence of the core supply voltage. You can verify that the microcircuit is malfunctioning by observing the absence of a PWM signal at pin 12 with an oscilloscope.

Figure 34 - Typical single-phase power supply circuits for the CPU

As an example of a malfunction of the power supply circuit of the EX98 board, one can note the failure, literally "burnout", of the parallel-connected transistors Q2 and Q3 CEB603AL. The performance of a board with such a defect was restored by replacing the faulty transistors with serviceable RFP50N06 (full name - RFP50N06LE) from "HARRIS" with the following parameters: Usi = 60 V; Iс = 50 A; rsi = 0.022 Ohm; built-in diode between drain and source; TO-220AB package.

Figure 35 - Typical multi-phase power supply for the CPU

Figure 36 - Block diagram of the CPU power supply system

The ADP3180 IC also issues a special Power Good signal (pin 10), a high level of which indicates that the output voltage level is in the range from -250 mV to +150 mV relative to the nominal. When these limits are exceeded, the corresponding comparator is triggered, the signal from which is fed to the input of the logic circuit, which generates the Power Good signal. When the rated voltage is exceeded by 150 mV, an internal CROWBAR signal is issued, according to which the channel control logic opens the lower keys of the half-bridges, which ultimately leads to a decrease in the output voltage. Thus, overvoltage protection is provided.

A typical malfunction is the failure of the transistor of the upper arm of one of the half-bridges, and this transistor may be punctured. In this case, when the computer is turned on, 12 V is supplied directly to the processor. The current consumption rises sharply, current protection is triggered in the computer's power supply. This happens almost instantly: the fan blades only have time to move a little. In this case, in no case should you try to turn on the power several times, and even more so turn on the motherboard without a processor - all this is fraught with burnout in the literal sense of the word with all the accompanying effects (smoke, flame) of some elements on the motherboard. The specified transistor 60TOZN manufactured by the Taiwanese company Advanced Power Electronics Corp (Uci = 30 V, Ic = 60 A, Rci = 12 m0m) can be replaced with the very common IRF3205 (Uci = 55 V, Ic = 110 A, Rci = 8 m0m) manufactured by the company

International Rectifier.

However, if power is supplied to the motherboard correctly, but there is no voltage on the processor, then you should start troubleshooting.

First of all, you should check the voltage level at the EN input (pin 11) of the PWM controller. It has to be tall. It may well be that the PWM controller simply does not turn on due to the fact that the motherboard circuitry blocks the activation of the API. The fact is that until the value of the VID code is set, the API should not be turned on. A special linear power supply with an output voltage of 1.2 V is used to power the processor circuit that produces the digital VID code.

Further troubleshooting and repair is carried out using the schematic diagram (Figure 2). Most APIs of modern motherboards, even for Pentium 4 processors in a 775-pin package, are almost the same.

3.1.6. Features of the design of modern hard disk drives, types of defects in the magnetic disk of hard disk drives

A modern hard disk drive (HDD) is a complex electronic-mechanical device. The drive elements are located on the electronic board and HDA (see Figure 36). The main element located on the electronic board is a microcontroller (specialized microcomputer), which controls the operation of all storage devices and organizes communication with the CPU. All data to be stored is located on a magnetic disk, which has the following logical organization (see Fig. 37):

Figure 37 - Block diagram of HDD

Figure 38 - Layout of data on disk

Service information

Service information is necessary for the functioning of the hard disk drive itself and is hidden from the user. Service information can be divided into four main types:

servo information, or servo markings;
low-level format;
resident microprograms (operating programs);
configuration tables and settings
defect tables.

Servo markup is necessary for the operation of the servo drive of the magnetic

HDD heads. It is according to the servo marking that they are positioned and held on the track. Service markings are written to the disk during production through special technological windows in the body of the assembled HDA. Recording is carried out by the drive's own heads using a special high-precision device - a servowriter. The movement of the head positioner is carried out by a special pusher of the servowriter in calibrated steps, which are much less than the inter-track intervals.

Work programs (microcode) control microcontroller are a set of programs required for the operation of a hard disk drive. These include programs for initial diagnostics, motor rotation control, head positioning, communication with the disk controller, buffer RAM, etc.

Hard disk manufacturers place some of the firmware on magnetic media not only to save ROM space, but also for possible prompt correction of the code if errors are found during production or operation. It is much easier to rewrite the firmware on the disk than to rewrite the "flashed" microcontrollers.

Configuration and settings tables drives contain information about the logical and physical organization of disk space. They are necessary for self-tuning of the electronic part of the disk, which is the same for all models of the family.

Defect tables. (defect-list) contains information about detected defective sectors

Modern hard drives usually have two main defect lists:

First P-list("Primary" - primary) is filled at the factory during the manufacture of the drive;
Second G-list("Grown" - growing), and is replenished during the operation of the screw, when new defects appear.

In addition, some HDDs also have

servo defect sheet(servo marks applied to hard disk drives sometimes also have errors),
pending defect list In it, the controller enters sectors "suspicious" from its point of view, for example, those that were not read the first time, or with errors.

The manufacturing technology of magnetic disks is very complex, control

The state of the surface of the disk is carried out at all stages of manufacturing, but even this does not allow obtaining the surface of the magnetic disk without defects. During the operation of the disc, the number of defects increases. Therefore, drive manufacturers have provided special methods for hiding defects that allow you to hide defects both during production and during operation.

(in the production of discs).

Currently, in the production of discs, several basic methods of hiding defects are used.

The first is to reassign the address of bad sectors to the address of the spare sector (Figure 38).

The method causes a loss of performance of the hard disk drive, since every time it detects a sector marked as unusable, it will be forced to move the heads to the spare area, which may be far from the defect site.

This method of hiding defects is called "replacement method" or remap (from the English "re-map": rebuilding the sector map). Currently not used in production.

Figure 39 - Sector reassignment methods

Second (main) way uses the following algorithm: after all defects are identified, the addresses of all healthy sectors are rewritten so that their numbers are in order. Bad sectors are simply ignored and do not participate in further work. The spare area also remains continuous and part of it is attached to the end of the work area to equalize the volume. This, the second main type of defect concealment, is called the "sector skip method". The new disc has no Bad sectors, a

the reserve area is continuous!

Figure 40 - Skipped sector method

Methods for hiding defective sectors when operating disks To hide defects in a domestic environment, the

substitution »Remap Substitution is performed automatically, this technology has received

the name is automatic defect reassignment, and the process itself is reassign.

Remap works as follows:

if an error occurs when trying to access a sector, the controller realizes that this sector is faulty and "on the fly" marks it as BAD.

Its address is immediately entered into the defects table (G-list).

During operation, the controller constantly compares the current sector addresses with the addresses from the table and does not refer to defective sectors. Instead, it moves the heads to the spare area and reads a sector from there. On the characteristics of the disk Vread = F (Ndor), as small dips on the graph of reading. The same will happen when recording.

System of operational monitoring of the state of the HDD - S.M.A.R.T.

Almost all hard drives released after 95 have a system of operational monitoring of their condition - S.M.A.R.T. (Self Monitoring And Reporting Technology).

There is some relationship between SMART attributes and surface condition. Some are directly related to bad blocks:

Reallocated sector count and Reallocated event count: number of reassigned sectors. These attributes show the number of sectors reassigned by remap in the G-list defect-list. They must be zero for new screws! If their value differs from zero, it means that the screw has already been used.

Raw read error rate: the number of read errors. These are "soft" errors that have been successfully corrected by the drive electronics and do not lead to data corruption. It is dangerous when this parameter drops sharply in a short time, passing into the yellow zone. This indicates serious problems in the drive.

Current Pending Sector: this attribute reflects the contents of the "temporary" defect list, which is present on all modern drives, i.e. the current number of unstable sectors. The screw could not read these sectors the first time. A constant value of this attribute above zero indicates a problem with the drive.

Uncorrectable Sector: shows the number of sectors, errors in which could not be corrected by ECC code. If its value is higher than zero, it means that it is time for the screw to do a remap.

Types of defects in the magnetic disk of hard disk drives
Hard disk drive surface defects are divided into the following groups:

Physical defects, which are subdivided into:
- Surface defects.
- Servo errors
- Hardware BADs.
Logical defects, which are subdivided into:
- Correctable logical defects (soft-bads)
- Fatal logic errors.
- "Adaptive" badges.

Surface defects... They arise from mechanical damage to the magnetic coating inside the sector space, for example, due to scratches caused by dust, aging pancakes or careless handling of the screw. Such a sector should be marked as unusable and removed from circulation.

Servo errors.According to the servo marks, the motor speed is stabilized and the head is held on a given track, regardless of external influences and thermal deformation of the elements.

However, in the process of using the disk, some servo tags may be destroyed. If there are too many bad servo tags, this place will start to fail when accessing the information track: the head, instead of taking the position it needs and reading the data, will start to jump from side to side. The presence of such errors is often accompanied by banging of heads, freezing of the drive and the inability to fix it with usual utilities. Elimination of such defects is possible only with special programs, by disabling defective tracks, and sometimes the entire disk surface.

The HDD cannot restore the servo format on its own; this is done only at the factory.

Hardware BADs. They arise due to a malfunction of the mechanics or electronics of the drive. Such problems include:

broken heads;
displacement of disks;
bent shaft as a result of impact;
dusting the containment area;
various "glitches" in the work of electronics.

Errors of this type are usually catastrophic and cannot be corrected by software.

Correctable logical defects (soft-bads): appear if the checksum of the sector does not match the checksum of the data written to it.

It occurs due to interference or power outage during recording, when the HDD has already written data to the sector, but did not have time to write the checksum.

At the next reading of such an "unfinished" sector, a failure will occur: the screw first reads the data field, then calculates their checksum and compares what was received with the written one. If they do not match, the drive controller will decide that an error has occurred and will make several attempts to re-read the sector. If this does not help (and it does not help, since the checksum is obviously incorrect), then, using the redundancy of the code, he will try to correct the error, and if this does not work, the screw will give an error to the external device. From the operating system side, it will look like BAD.

Fatal logic errors. These are errors of the internal format of the hard drive, leading to the same effect as surface defects. They occur when the sector headers are destroyed, for example, due to the action of a strong magnetic field on the screw. But unlike physical defects, they can be corrected by software. And they are called incorrigible only because to correct them it is necessary to do the "right"

low-level formatting, which is difficult for ordinary users due to the lack of specialized utilities.

"Adaptive" badges. Despite the fact that the screws are very precise devices, during their mass production, there is inevitably a scatter in the parameters of mechanics, radio components, magnetic coatings and heads.

Therefore, all modern screws are individually tuned during manufacture, during which such parameters of electrical signals are selected, at which the device works better.

This setting is carried out by a special program during technological surface scanning. In this case, so-called adaptives are generated - variables that contain information about the features of a specific HDA. Adaptives are stored on disks in the service area, and sometimes in Flash memory on the controller board.

During the operation of the screw, the adapters can be destroyed.

"Adaptive" beds differ from the usual ones in that they are "floating". Adaptive bads are treated by running selfscan "a - the internal program

testing similar to that used at the factory for the manufacture of screws. At the same time, new adaptives are created, and the screw returns to its normal state. This is done in the conditions of branded service centers.

3.1.7. Hardware malfunctions of hard disk drives, their nature of manifestation, methods of their elimination

Typical causes of hard disk drive hardware malfunctions can be roughly divided into the following groups:

Malfunctions due to natural aging of the HDD;
Malfunctions due to incorrect operating mode;
Malfunctions associated with design errors.
Malfunctions due to natural aging of the HDD.

Malfunctions due to natural aging of the HDD
With proper operation and compliance with all technical requirements, a well-made storage device exhibits a natural aging process. Magnetic disks are most susceptible to it.

First, over time, the magnetization of the minimum information prints weakens, and those sections of the discs that were previously read without problems begin to be read not the first time or with errors.

Secondly, the aging of the magnetic layer of the discs occurs.

Thirdly, scratches, chips, cracks, etc. appear on the plates. All this leads to the appearance of damaged sectors.

The normal aging process of discs is quite long and usually takes 3 ... 5 years.

It should be noted that continuous operation mode is most favorable for HDD, not start / stop. Therefore, drives serve for a rather long time in constantly working servers located in a special room or rack, where normal climatic conditions are maintained.

Malfunctions due to incorrect operation

The most common reason for HDD failures is the following, the main destructive factors of which are:

overheat,
shock loads
power surges.

An important temperature indicator is the rate of temperature change, which should not exceed 20 ° C / hour in working condition and 30 ° C / hour in non-working condition. Exceeding the warm-up rate is very dangerous for the drive mechanics and is called thermal shock.

Mechanical effects on the HDA are detrimental to the precision mechanical parts of the drive. The impact on the HDA causes vibrations of the heads, which produce a series of impacts on the surface of the discs, which inevitably leads to mechanical damage to the plates and heads.

A low-quality power supply unit for a personal computer can pose a serious danger to the electronic part of the hard drive. The supply voltages must be within the range of +5 V ± 5% and +12 V ± 10% with a permissible ripple amplitude of 100 mV and 200 mV, respectively.

Malfunctions due to design errors

Recently, the quality of hard disk drives has decreased, as evidenced by a significant reduction in the warranty period of operation by major manufacturers.

Bad contact in the pin connector between the electronics board and the preamplifier chip on the head assembly. As a result of poor contact in the connector, incorrect information is written into the technological bytes of the sector, for example, in the field of the CRC code. This defect can lead to damage to service information, which the drive will not be able to recover the next time the power is turned on.

Poor soldering of microcircuits at the manufacturer. Such defects appear after about a year of drive operation, when during normal operation the drive suddenly turns off and does not start anymore (“freezes”) or starts to “knock” heads, which can damage the mechanics and / or service information.

Low-quality microcircuits that fail during prolonged heating, not exceeding the permissible limits. The defect can be corrected by replacing the microcircuit.

Imperfect design of the hydrodynamic bearing, leading to the formation of chip particles in the lubrication cavity and, as a result, seizure of the spindle motor.

Poor fastening of the disc to the spindle, as a result of which the runout of the disc constantly increases and causes the destruction of the bearing in the spindle motor; noise appears during the operation of the drive, and after a while - defective sectors, since the "distant" tracks begin to be poorly read due to the beating of the disk.

Poor quality EEPROM (flash) microcircuits, which can lose the stored firmware due to charge leakage during heating. You can overwrite the ROM on a special programmer or in the technological mode of the drive.

Errors in the drive management firmware. Drive manufacturers do not publish information about the nature of errors and their consequences, but they release firmware updates quite regularly.

Disk Failure Symptoms First and Most Popular-when power is applied to the disk, it does not

nothing happens at all, he is completely silent and does not even spin the spindle motor, or he tries to do it, but does not pick up the required speed. A similar symptom may be present because the engine itself has jammed, or the heads have fallen on the disc and stuck to it (this happens on almost all modern discs, since the heads are perfectly polished and a diffusion effect occurs).

Second malfunction- the disc spins normally, but there is no unparking of the heads - a characteristic quiet click. This rarely happens, because often, the head positioning control (servo system) and a three-phase generator for the spindle motor are placed on the same crystal, and if it fails, then, as a rule, all at once or unparking does not occur because the positioning coil on the head block has broken.

Third fault-disk is normally recalibrated when the power is turned on and does not emit extraneous sounds, but at the same time it is not detected in the BIOS, and the model name does not correspond to the one written on the disk itself, or there are incomprehensible characters in the name. In this case, the main interface chip on the electronics board is often defective. It is strongly discouraged to write to such a drive. If the data bus is defective, the data on the disc can be damaged.

Fourth malfunction- associated with a defect in microcircuits, which degrade from constant thermal expansion (temperature gradient). A malfunction manifests itself mainly with warming up, i.e. the disk works fine for a while, and then starts to rattle, knock or stop the engine.

IDE HDD hardware malfunctions can be divided into the following groups:

malfunction of initial initialization;
malfunction of the spindle motor control circuit;
malfunction of the positioning control circuit;
malfunction of the data read-conversion channel;
malfunction of the recording channel, data precompensation circuit;
destruction of service information.

Initialization faults lead, as a rule, to
complete inoperability of the drive.

In a hard disk drive with such a malfunction, very often even the spindle motor does not start (due to the fact that the control microprocessor does not give permission to start) or starts, then stops and starts again, etc., but in all cases the hard disk drive does not generate a 50H code in status register.

The main reasons why the drive's control microprocessor cannot perform initial initialization:

malfunction of the reset circuit;
malfunction of the quartz clock generator;
destruction of the control microprogram in the program memory;
malfunction of the control microprocessor;
malfunction of a single-chip microcontroller.

To localize the malfunction: It is necessary to check:

supply voltages on the control microprocessor single-chip microcontroller,
excitation of a quartz resonator connected to the control microprocessor, or the arrival of clock pulses if an external generator is used,
all drive synchronization schemes.

Check the hard drive reset circuit.

To do this, close and open contacts 1 and 2 of the interface connector of the drive and the oscilloscope observe the passage of the "RESET" signal to the control microprocessor and single-chip microcontroller.

If clock pulses come to the control microprocessor (or a quartz resonator connected to the microprocessor is excited) and the reset circuit works, then the microprocessor must execute the control program, as evidenced by the pulses on the ALE, RD, WR pins.

If a quartz resonator connected directly to the microprocessor is not excited or there are no pulses at the ALE pin, then the drive's control microprocessor is most likely faulty.

Figure 41 - Typical spindle motor control circuit diagram

Malfunction of the spindle motor control circuit.

If you turn on the power to the drive spindle motor not starts up, it is necessary to make sure that the HDA is in good working order by connecting the good electronics board to it.

If this is not possible, then they check the resistance of the windings (phases) of the spindle motor, which should be approximately 2 ohms relative to the middle terminal, and then proceed to troubleshooting on the control board.

Sometimes the start of the spindle motor is not possible due to the adhesion of the magnetic heads to the disks.

The criteria for starting a spindle motor are:

The presence of a supply voltage on the control microcircuit,
Availability of a reference clock frequency
Presence of a start enable signal.

After turning on the power, the presence of motor start pulses with an amplitude of 11 - 12 V is monitored in three phases on contacts J14, J13, J12 (see Figure 40). If, for any of the phases, the voltage is less than 10 V, then m / s U3 is faulty. With such a malfunction, the spindle motor cannot gain rated speed and, as a result, the magnetic heads do not unpark.

The rotation speed of the spindle motor can be controlled by the INDEX pulses at the E35 control point (with the board installed on the HDA). The INDEX pulse repetition period is ~ 12 ms, the INDEX pulse width is ~ 140 ns.
Controlled by m / s U3 signal START. To start the spindle motor

START = 1, to stop START = 0.

The phase distribution is occupied by m / s U6 from its terminals Fc1 - Fc6, the amplitude of the TTL control signals.

Rotation speed feedback is carried out via the servo data read line (SERVO DATA).

In turn, the m / s of the U6 sync controller generates a servo tag search signal (SERVO GATE) for ms. U11.

In the absence of special diagnostic equipment and software, the primary diagnostics of the HDD can be performed by connecting it to a separate power supply. The diagnostic tool in this case is the operator's hearing.

When the power is turned on, the HDD performs: untwisting the spindle motor, at which a growing sound is heard (4 ... 7 s), followed by a click when the heads are removed from the parking zone and a very characteristic crackling sound accompanying the recalibration process (1 ... 2 s) ...

The recalibration indicates at least the health of the reset circuit, the clock generator, the microcontroller, the spindle motor control circuit and the positioning system, the data conversion read channel, as well as the health of the magnetic heads (at least one - with the help of which the initialization process takes place) and safety service information of the drive.

For further diagnostics, the hard drive is connected to the Secondary IDE port, and in the BIOS, in the SetUp procedure, it is necessary to automatically detect the connected drives. If the model of the diagnosed HDD is recognized, the operating system is loaded and the diagnostic software is launched.

The simplest diagnostics consists in an attempt to create a partition on the drive being diagnosed (using the FDISK program) and the subsequent formatting procedure (Format d: / u). If defects are found during formatting (verification), information about them will be displayed on the computer screen. Detailed diagnostics of HDDs is carried out by special programs.

3.1.8. HDD file system malfunctions and methods of their elimination

Logical disk organization.

The operating system of any hard disk, regardless of size, is represented as a data storage location consisting of two areas - the system area and the data area. The system area plays an auxiliary role and serves to organize data storage (forms the file system of the disk), under normal conditions this area is not accessible to the user. The block diagram of the system area device is shown in the figure.

Figure 42 - Layout of data on disk (logical disk organization)

MBR-(Master Boot Record) - master boot record.

PT-(Partition Table) - partition table. NSB-(Non-System Bootstrap) non-system bootloader

BA (Boot Area) - operating system boot area BR (Boot Record) - boot record OC .

ROOT-Root directory of the disk
SMBR-(Secondary Master Boot Record) - secondary MBR
LDT- (Logical Disk Table) logical disk partition table.

Any violations in the system area appear as file system errors.

Diagnosing file system violations

The reasons for the violation of the file system can be diagnosed by paying attention to the messages that appear:

If the entire message is in upper case (i.e. in capital letters), then this BIOS does not find the MBR on the device specified in the Setup, which indicates a read error or the absence of a system sector sign for the first disk sector (i.e. not marked up). To make sure that everything is fine with the disk, you need to go to BIOS Setup and run Autodetect.
Messages " Invalid partition table " and belong to the bootloader from the MBR; the boot sector of the active partition is either not readable, or it is not yet (or already) absent.
Posts "Invalid system disk" and "Disk I / O error" issues the bootloader from the boot sector, reporting the absence of operating system files or an error on the disk.

Causes of occurrence:

If the problem is not related to the disk itself, you need to seriously understand where the system sectors have gone.

In the second case, there is either a violation of the PT table, or the destruction of the boot sector.

In the third case, the system files could be deleted or damaged, you can try to fix the situation by booting from a floppy disk and entering the command

"sys c: \".
Signs of destruction of the partition table.

The section has disappeared from Explorer. Empty space is displayed when you run the Disk Management utility. Or ghost partitions may appear, and the summation of the volumes of all logical disks exceeds the size of the hard drive itself. This means that some sections overlap with each other.

The system cannot boot, but displays messages like "Bad or missing partition table" or "Error loading operating system".

Windows shows a blue screen that says "STOP: INACCESSIBLE_B00T

Reasons for the destruction of the partition table

Invalid deletion of the wrong partition. This option is the least dangerous because all data remains in place, but there is no access to it.

Breaking the chain of sections. This happens in the case of damage to the EPP (Indexes of Extended Sections).

Simultaneous destruction of MBR and EPP.

Manual recovery of partitions and information:

To recover lost (damaged) data, you need information about:

The likely partitioning of the disk and the number of logical drives.
The size and history of the creation of logical drives. The history of creation implies possible artificial changes in the size of disk partitions.
Features of the FAT or NTFS file system.
The type and version of the Operating System (DOS, Win) used on the disk.
Unique names of directories and files located in the root directory of drive C, the name of the directory with data subject to priority recovery and unique names of files and subdirectories located in this directory.

For manual data recovery, you can use the following utilities:

DiskEdit from Norton Utilities
Tiramisu(http://www.recovery.de) or Hard Drive Mechanic.
UnFormat(from the same Norton Utilities suite).
NDD - Norton DiskDoctor(included with Norton Utilities).

Disadvantages:

It is necessary to know the initial logical organization of the disk and the peculiarities of the organization of FAT, NTFS and Linux systems.
Can only be used by trained users.
it takes a long time.

When using any of the above programs for manual recovery, you should adhere to the following sequence of actions:

1. DIAGNOSTICS OF DAMAGE.

1.1) Launch DiskEditor and, switching it to the mode of viewing the damaged disk at the physical level, sequentially check the integrity of RT, MBR, FATs, ROOT and DA.
At this stage, try to find out (if it is not known for certain) the file system type of the first disk partition (FAT16 or FAT32).

1.2) If any elements of the disk structure are intact, save them as files on a backup disk. For example: MBR.HEX, BR1.HEX, FAT01.HEX, FAT02.HEX, ROOT0.HEX.

1.3) Further recovery of the disc depends on the degree and nature of the damage.
If any copy of FAT remains intact (or at least partially) on the first partition of the disk, the information can be restored almost in full.

2. TEMPORARY DATA BACKUP.

In order to preserve the possibility of recovering files located at the beginning of the disk, it is advisable to make a backup copy of the initial sectors of the disk that undergo changes during the recovery process.

In DiskEditor, select the view mode for the first 500-1000 physical sectors of the disk and save them as a file on the backup disk.

3. RESTORATION Partition Table.

When recovering PT, it is necessary to take into account the disk size and the peculiarities of the FAT16 or FAT32 disk file systems.

In the case of recovering disk partitions with a FAT32 file structure, it makes sense to use the MRecover program. This program allows you to quickly find and recover "lost" hard disk partitions by writing all the necessary data to the partition table (s).

4. Recovery BR, FAT and ROOT.

4.1 Recovery of BR, FAT and ROOT copies is easier to perform in an "automatic" way.

4.2 Perform a standard formatting of the main disk partition, i.e. team format WITH:. In this case, the file structure of the formatted disk partition is formed with the reconstruction of BR, clean FAT and ROOT, while the data area is not affected, i.e. the information in DA does not change and your data does not disappear.

4.3 If there are surviving FAT and / or ROOT images backed up as files, use DiskEditor to restore them to the disk. If you have a second copy of FAT, but the first one does not, you should copy the second copy and replace the first copy.

Automatic disk partition recovery programs

There are many programs for automatic file system recovery, their principle is in many ways similar. Let's consider the principle of using automatic disk partition recovery programs using the program as an example: ACRONIS RECOVERY EXPERT(www.3cronis.fu)

This application is part of the Acronis Disk Director Suite. The interface is Russian.

The program is intended for recovering partitions deleted by accident or as a result of a system failure. It works in manual or automatic mode. Figures 42-45 show the sequence of work with the program.

Figure 43 - Window for selecting the operating mode

Figure 44 - The result of the analysis of the state of the disk

Figure 45 - Search for deleted partitions

Figure 46 - The result of the analysis of the state of the disk

At the end of the work, the user will be shown all partitions that can be restored

Experiments have also shown that the program is completely insensitive to the way the partition was ditched. In theory, it is possible to recover even when another logical drive has been placed in place of the deleted logical drive.
The application works not only with FAT and NTFS, but also with Linux partitions.

3.1.9. Typical OS malfunctions, an algorithm for their search and elimination

The most common reasons for failure to boot the OS are as follows
Windows 2000 / XP:

damage or deletion of important system files, for example, system registry files, ntoskrnl.exe, ntde-tect.com, hal.dll, boot.ini;
installing incompatible or faulty services or drivers;
damage or removal of services or drivers necessary for the system;
physical damage or destruction of the disk;
damage to the file system, including violation of the directory structure, master boot record (MBR) and boot sector;
the appearance of incorrect data in the system registry (if the registry is not physically damaged, the records contain logically incorrect data, for example, outside the range of acceptable values for services or drivers);
incorrectly set or too limited access rights to the \% systemroot% folder.

OS recovery tools can be divided into:

regular included in the Windows 2000 / XP distribution
third party utilities.

Standard System Recovery Tools Rescue Disk
Windows XP employs the Automated System Recovery (ASR) system, which allows you to back up the entire system using modern and common high-capacity media such as CD-R / RW or hard disks (also tapes, if someone has there is a streamer).

Creating an ASR set.

In order to take advantage of the ASR mechanism, you need to create an ASR set, consisting of 2 parts:

direct archive with data, which can be placed on a recordable CD, magnetic tape, non-system partition of the hard disk or other hard disk;
a floppy disk that stores data required for system recovery.

Users with administrator rights can create ASR sets. To create an ASR set, run the program "Data Archiving"

("Start - All Programs - Accessories - System Tools - Back Up Data" or type ntbackup.exe from the "Start - Run" menu). Switch to advanced mode. By default, not all files are included in the generated archive. Therefore, before creating an ASR set, it is worth looking at the list of excluded files.

To do this, go to the "Tools - Options - Exclude Files" tab. By default, this list includes: the paging file (pagefile.sys), the hibernation file (hiberfil.sys), restore checkpoints, temporary files, and some log files. Check the entire list carefully and make changes if necessary. You can then run the Disaster Recovery Preparation Wizard to create an ASR set - select Tools - Disaster Recovery Wizard. Specify the path for the archive to be created. Do not specify the system partition of your hard disk as the path. After collecting the necessary information, the archiving process will begin. If you place an archive on a hard disk partition with the FAT32 file system, pay attention to the information line "Expected, bytes" - if the size of the created archive is estimated at more than 4 GB, you should interrupt the archiving process and reduce the archive size by excluding some non-system files from it which can be saved in a separate archive, otherwise the ASR set creation will not complete as expected. Then run the Disaster Recovery Preparation Wizard again. After creating the archive, you will be prompted to insert a floppy disk to write the recovery parameters on it. This completes the creation of the ASR set.

Recovering your system using the ASR kit

To restore the system, you will need an ASR kit (archive + floppy disk) and a Windows XP boot disk. Boot using the boot disk, select Windows XP installation. When prompted in the status bar, press F2 and the message "Insert the disc titled Windows AutoRecover Disc into your floppy drive" appears. After reading the data necessary for recovery from the floppy disk and loading the main drivers, the system partition will be formatted and the initial installation of Windows XP will be performed. Next, the System Emergency Restore Wizard will be launched and the files from the ASR set archive will be restored. After restoring the files, a reboot will be made and you will get Windows XP with all installed programs, documents and system settings at the time of creating the ASR set.

Emergency Recovery Console

Another system recovery tool is the Emergency Recovery Console (ERC for short) included in the Windows 2000 / XP distribution. You can install ERC on your computer only after installing Windows 2000 / XP, for which you need to do the following:

press the "Start" button; select the "Run ..." item in the expanded menu;

in the window that opens, enter the following command:
M: \ i386 \ winnt32.exe / cmdcons, where M is the drive letter,
matching CD-ROM drive; click the "OK" button;
follow the instructions on the screen;
restart the PC when the installation is complete.

Installation will require about 6 MB in the system partition. Now in the OS selection menu that appears at system startup, there will be a new item - "Windows 2000 Recovery Console" or "Windows XP Recovery Console". By choosing this item,

you will start downloading the ERC

After starting the Recovery Console, you will need to select the installed operating system (if two or more systems are installed on the computer) and enter it using the administrator password. If the entered password turns out to be correct, we can boot into the command line interface. From it, by typing certain commands, you can try to restore the system. Using the basic commands provided by the console, you can perform simple actions such as changing the current folder or browsing it, as well as more complex ones, such as restoring the boot sector. For help with the commands in the Recovery Console, enter the word “help” at the console command line. The most important commands in the Recovery Console are:

overwriting the registry - copy

displaying a list of system services and drivers - listsvc

disabling a specific service - disable(turning on - enable)

recovery of boot files - fixboot

Recovery Master Boot Record - fixmbr

Rollback driver

Very often, a system crash occurs when updating the driver of a device. Since the driver is essentially the same program, it sometimes contains errors that, in some configurations, lead to incorrect operation and, as a result, to system failure. When updating a device driver, Windows does not delete the old one, but saves it in case problems arise. And when a new driver causes problems, the Rollback Driver tool allows you to revert the old one, that is, to roll back the changes to the system. Moreover, the built-in driver compatibility check mechanism may prevent the installation of a driver that Windows XP believes is not suitable for it.

System restore

System Restore, allows you to return the OS to a healthy state based on the concept of restore points (Restore Points). The idea is simple, like everything ingenious: to make the system itself track and record all changes that occur to the system files. Such a mechanism makes it possible to rollback to a working version of the system if the system files are damaged by illiterate user actions or the installation of incorrect drivers or programs. The System Restore mechanism automatically saves a set of system files before installing drivers or programs, and a system restore point is created once a day. When you start this service, you will be prompted to choose - to restore the system in accordance with the previously saved restore point or create a new restore point. Choose what you want and then just follow the instructions that appear on the screen. If the computer does not boot, try opening Last Known Good Configuration. Windows XP will restore the system using the latest restore point. Since each restore point takes up space on your hard drive, it makes sense to delete unnecessary ones. To do this, do the following: "Start -> Programs -> Accessories -> System Tools -> Disk Cleanup", the "Advanced" tab. "All points are deleted except the last. Also in the registry, you can set the lifespan of restore points by adjusting the parameter

RPLifeInterval under: HKEY_LOCALMACHINE \ SOFT-WARE \ Microsoft \ Windows NT \ CurrentVer-sion \ SystemRestore. Parameter type - dword The default value in seconds is 0076a700, which corresponds to 90 days.

System registry backup tools

The registry is a huge database of settings stored in folders at% SystemRoot% \ System32 \ Config and the Ntuser.dat user profiles folder. A thoughtless change of parameters or, even worse, deleting entire branches can lead to the inoperability of the system as a whole. You can use one of the following methods to back up the registry:

Method number 1 The operating system, on each successful startup, saves a copy of the registry in a .cab file, which is written to the hidden SYSBCKUP directory of the Windows directory. By default, the last five copies are kept.

To restore the registry from one of these backups, you need to reboot into DOS and run the command SCANREG / RESTORE.

A list of available registry backups will appear, sorted by the time they were created. After selecting the desired copy, the data will be safely

restored, and you will receive a register that corresponds to the state of affairs at the time of its creation.

To back up the registry at any time, use the command SCANREG / BACKUP, which, in the case of a normally passed check, will create a backup copy.

Method number 2 To create a backup copy of the registry, you can use the Backup and Restore Wizard - Start / Programs / Accessories / System Tools / Backup Data - or just Run: ntbackup. The backup utility allows you to back up copies of important system components such as the registry, boot files (Ntldr and Ntdetect.com), and the Active Directory database. To back up the Windows XP registry, the step-by-step instructions are as follows:

We go into the system with administrator rights.
Launch NTbackup - Data Archiving.
From the wizard mode, go to the Advanced mode.
Select the Archiving tab.
In the left window we find the System State icon (line) and mark it with a "birdie":
Click on the Archive button, and then select Advanced.
We set the checkbox "Data verification after archiving"; remove from the item "Automatically archive protected system files along with the system state" (the procedure will take much less time):
Set the archive type to Normal.
OK and Archive button

The step-by-step instructions for a full registry restore using NTbackup are as follows:

We enter the system with administrator rights.
Launch NTbackup.
Go to the Media Recovery and Management tab.
In the Check boxes list for all objects that you want to restore, check the box for the System state object.

Method number 3. The essence of this method is the so-called export of the reg file. The method is especially effective (it takes a little time and allows you to make copies of individual subsections) and is relevant when experimenting with the registry. Algorithm:

Run the regedit command.
Select the desired section / subsection.
Right mouse button / export, specify the path to save the copy and the file name.

When archiving a part of the registry, the data is exported to a reg-file. In order to extract them and restore the original state of the registry, you must perform the following steps:

Launch regedit: Start / Run / regedit.
from the main menu, select File / Import, indicating the path to the imported file, or simply run the reg-file, confirming the import into the registry.

3.1.10 Malfunctions of the flotation device, their nature of manifestation, the method of their elimination

The main internal elements of the drive are the frame, the spindle motor, the drive head assembly, and the electronics board.
NGMD includes:

disk drive,
disk control controller,
device for positioning the GCHZ on the desired track,
device for reading and writing information,
locking devices.

The spindle motor is a flat multi-pole motor with a constant rotation speed of 300 rpm. The motor for the drive of the head block is a stepper, with a worm, gear or belt drive. To identify the properties of the floppy disk, three mechanical sensors are installed on the electronics board near the front end of the disk drive: two - under the holes for the protection and the recording density indicator, and the third - to determine the moment of lowering the floppy disk.

HMD has 4 holes:

for the motor axis,
window for GCHZ,
for indexing a sector,
for write protection of information.

The floppy disk inserted into the slot gets inside the diskette frame, where the protective curtain is slid off it, and the frame itself is removed from the stopper and lowers down, the metal diskette ring rests on the spindle motor shaft, and the lower surface of the diskette - on the lower head (side 0 ). At the same time, the upper head is released, which, under the action of a spring, is pressed against the upper side of the diskette.

On most drives, the frame lowering speed is not limited in any way, due to which the heads strike a noticeable blow to the surfaces of the floppy disk, and this greatly reduces their reliable operation.

In some models of drives (mainly from Teas), a microlift retarder is provided for smooth lowering of the frame. To extend the life of floppy disks and heads in drives without a microlift, it is recommended to hold the drive button with your finger when inserting a floppy disk, preventing the frame from dropping too abruptly.

On the shaft of the spindle motor there is a ring with a magnetic lock, which at the beginning of the rotation of the motor tightly grips the ring of the floppy disk, at the same time centering it on the shaft. In most drive models, the signal from the floppy lowering sensor causes the engine to momentarily start in order to grip and center the floppy disk. The floppy drive connects to the controller using a 34-wire cable, where even wires are signal and odd wires are common. The general version of the interface provides for connecting up to four drives to the controller, the version for the IBM PC - up to two.

In general, the drives are connected completely parallel to each other, and the drive number (0 ... 3) is set with jumpers on the electronics board; in the version for the IBM PC, both drives are numbered 1, but are connected using a cable in which the selection signals (wires 10-16) are reversed between the connectors of the two drives.

Sometimes pin 6 on the drive connector is removed, which in this case plays the role of a mechanical key. The drive interface is quite simple and includes signals for selecting a device (four devices in general, two for an IBM PC), starting the engine, moving heads one step, enabling recording, read / write data, as well as information signals from the drive - start tracks, a sign of setting the heads to the zero (outer) track, signals from sensors, etc. All work on coding information, searching for tracks and sectors, synchronization, and error correction is performed by the controller.

Table 16. Distribution of signals on the connector (ribbon cable) of the floppy disk drive interface - floppy disk drive

Contact No.	Appointment	Direction
odd

	indicator control
	not used
	index
	drive selection 0
	drive selection 1
	drive selection 2
	turn on the motor
	direction

	data recording
	recording resolution
	track 00
	write protection
	reading data
	head selection
	willingness

Standard HD (High Density) floppy disk format

80 tracks on each side, each track has 18 sectors of 512 bytes. Compressed format - 82 or 84 tracks, up to 20 sectors of 512 bytes or up to 11 sectors of 1024 bytes.

Basic requirements for storage of GMI

Store in packages and disks.
Do not write on them with a pencil or ballpoint pen.
Do not quit, do not "test for kinks."
Keep away from power sources, magnets and heat sources near electromagnetic emitters.
Destroy damaged KMTs.
Use quality and branded GMI.
Check the GMI regularly for the virus.
Remember that cheaper HMDs have a thinner magnetic layer that crumbles easily, reducing the HMD's performance.

Prevention of NGMD

Prevention can be carried out in accordance with the following guidelines:

Estimate the daily operating time of the drive with the LED lit;
clean it monthly with a vacuum cleaner;
some manufacturers of floppy disk drives recommend monthly demagnetization of the drive heads;
check the drive speed, head alignment (using a special alignment disk) every six months;
as floppy disk heads become dirty, clean them with a non-abrasive, abrasive, or "wet" cleaning floppy disk; you can also clean it by hand with alcohol. A useful rule: clean the read (write) head every 40 hours of operation of the floppy disk drive;

The GMD control controller is made on one or several LSIs. The read signal from the GCHZ is fed to the controller in a sequential code,

after that, in parallel code, it goes to the data buses of the microprocessor. The nominal frequency of the GCHZ usually varies in the range of 62.5-250 kHz.

The positioning device, depending on the standard of the disk, provides an accurate selective installation of the GCD block on the track. There are 2 sensors in the NGMD - a track start marker sensor and a track "00" sensor (DND). DMND is triggered when the hole on the HMD falls into the gap between the LED and the photo-transistor.

This generates a track start marker pulse with a duration of at least 600 ms.

DND is usually performed in two forms: either with the help of a photodiode and an LED, the extreme "00" track is fixed, or with the help of a block contact, which fixes the extreme position of the code screw of the stepper motor moving the GCHZ.

Diagnostics of malfunctions of floppy disk drive

It so happens that on a normally working computer, a floppy drive does not read or write information on floppy disks poorly. Most often, this indicates the poor quality of the floppy disks themselves. However, if floppy disks can be read normally on other computers, then you should conclude that the drive is faulty.

Before diagnosing a faulty floppy disk drive, make sure that all express tools available to the user have been tested, namely: check the reliability of the cable connection between the MV and the floppy disk drive, the presence of +5 V and +12 V supply voltages in the floppy disk drive.

Make maximum use of audible and visual error indications. For example, if an error appears when starting the PC, then in the event of a faulty floppy disk drive, one short signal sounds and a system error code lights up on the display:

Code 6XX, for example: code 601 - diskette error or controller board, cable, floppy drive is faulty;

Code 602 - Diskette Boot Record error;

Code 606 - a malfunction in the drive design or on the floppy disk drive controller board;

Code 607 - the disc is write-protected, the disc is not inserted correctly, the disc write-protect switch is bad, the analog part of the floppy disk drive electronic board is defective;

Code 608 - GMD is faulty;

Code 611-613 - malfunction on the drive controller board or in the drive data cable;

Code 621-626 is a malfunction in the design of the drive.

If the malfunction cannot be localized, then you should try the drive to another system unit and repeat the boot. If it fails again, then the drive unit itself with its electronic board is faulty.

Most often, the electromechanical part of the drive design is faulty, namely, the drive of the drive, the stepper motor for moving the GChZ, the index sensor does not function, the GChZ failure, the GChZ alignment is down, etc.

By the way, misalignment of the GCD is quite common. The PC user must skillfully use the existing diagnostic software tools for drives, which can quickly isolate the fault. After localizing the faulty board or unit, the user can start repairing them.

The main reasons for a floppy disk drive malfunction may be the following reasons:

the type is set incorrectly in SETUP (SETUP "flew") - set correctly;
the contact in the connectors is broken - open the case, remove the cable, carefully put it back on;
the controller of the floppy drive (multicard) is faulty - as a rule, the computer itself, when turned on, reports this - replace the m / s MIO;
contamination of the drive - use a special cleaning floppy;
a really serious breakdown requiring replacement of the drive.

To facilitate the diagnostics of flotation devices, the Teas company (Japan) proposes to carry out 15 general checks, of which the first four are mechanical, and the rest are electronic.

It should be noted that all diagnostic drives have a set of checkpoints. For example, Teas FD-55BR / FR / GR drives have 8 control points, namely:

TP1- INDEX - check the index signal,
TP2 - Erase gate delay - delay of the erasing signal,
TRZ-TRACK OO - signals of the zero track index,
TR4-Prge-AMR - signals of the recording amplifier of the 1st side,
TR5-Rge-AMR - recording amplifier of the 2nd side of the floppy disk, "
ТР6- DC О - signals of the zero track,
TP7- DIF.AMP - signals of the 1st side readout amplifier,
TP8- DIF.AMP - signals of the 2nd side readout amplifier.

Sometimes the floppy disk drive reads information only from those floppy disks that were previously formatted on it. This may be due to the following:

the alignment of the block of magnetic heads is broken,
the zero track sensor is displaced,
the rotation speed of the disk drive has changed,
faulty quartz of the master oscillator of the NGMD controller.

Sometimes there is a situation when a floppy drive only reads the first inserted floppy disk, and all subsequent ones do not. The cause of this malfunction is the lack of a signal about the change of a diskette (DC-disk changed), which passes along the 34th wire of the interface. The diskette change sensor is an optoelectronic pair installed in the drive. Therefore, more precise reasons may be:

contamination or malfunction of the optocoupler;
violation of contacts in the connectors to which the interface is connected;
break of the 34th wire in the loop;
malfunction of the controller on the board (possibly a broken track).

3.1.11 GCD malfunctions, their nature of manifestation, methods of their elimination

GCD device
A typical GCD drive consists of

electronics boards,
spindle motor,
optical readhead system
Disc boot systems.

On electronics board all control circuits of the drive, interface with a computer controller (IDE, SATA), interface connectors and audio signal output are located.

The spindle motor is used to drive the disc in rotation at a constant or variable linear speed.

On axis spindle motor a stand is fixed to which the disc is pressed after loading. The disc is pressed against the stand using a washer located on the other side of the disc. The pad and washer contain permanent magnets, the force of gravity of which forces the washer through the disc against the pad.

Optical system consists of a carriage on which a laser emitter, a focusing system and a photodetector are located, and a mechanism for its movement. The focusing system is a movable lens driven by an electromagnetic system. Changing the magnetic field strength causes the lens to move in the vertical plane and refocus the laser beam.

Moving system The head has its own miniature motor that drives the carriage using a worm gear (sometimes gear).

How gcd works

A semiconductor laser generates a low-power infrared beam that hits a reflective mirror. The servo motor moves the movable carriage with the reflective mirror to the desired track on the CD in response to commands from the built-in microprocessor. The beam reflected from the disk is focused by a lens located under the disk, reflected from the mirror and hits the separating prism. A separating prism directs the reflected beam to another focusing lens. This lens directs a reflected beam onto the photo sensor, which converts the light energy into electrical impulses. The signals from the photosensor are decoded by the built-in microprocessor and transmitted to the computer in the form of data.

Figure 47 - Block diagram of the optical head Figure 48 - Optical head In accordance with this structure, three main groups of GCD malfunctions can be distinguished:

mechanical failures;
optical system malfunctions;
malfunctions of electronic components.

Mechanical faults make up 80 ... 85% of the total number of faults. They can be divided into several main groups:

lack of lubrication of rubbing parts;
accumulation of dust and dirt on the moving parts of the disc transport mechanism;
salting of friction surfaces;
violations of regulations;
mechanical breakdowns of parts of the transport mechanism.

Lack of lubrication causes the CD-ROM to have difficulty pushing out the disc carriage. In simple mechanisms, where each element performs several functions, the lack of lubrication leads, for example, to jamming of the carriage lock and excludes the possibility of using a CD-ROM.

The accumulation of dust and dirt on the moving parts, especially on the edges of the moving carriage carriage, makes it almost impossible to lock the mechanism, and as a result the CD-ROM constantly ejects the disc.

Filling the friction surfaces leads either to a stop of the carriage mechanism in intermediate positions, or to slipping of the disc during rotation. Both make the use of CD-ROM impossible. Violation of the regulation of the transport mechanism leads to a similar result.

Lack of lubrication of the mechanism results in the drive having difficulty pushing out the disc holder with the disc. It is advisable to periodically lubricate the transport mechanism of the CD-ROM drive with lithol

Malfunctions of the optoelectronic information reading system.

Despite its small size, this system is a very complex and accurate optical device. In terms of the frequency of occurrence during the first one and a half to two years of operation, failures of the optical system make up 10 ... 15% of the total number of failures.

The main parts of the system are (see Figure 48):

servo drive rotation control;
servo positioning system of the laser reading device;
autofocus servo system;
radial tracking servo system;
reading system;
laser diode control circuit.

Figure 49 - The structure of the links of the optoelectronic information reading system

Disk rotation servo control provides a constant linear speed of the readout track on the disk relative to the laser spot.

Typical signs of a malfunction are either the lack of rotation of the disk, or, conversely, acceleration to maximum rotation speed. When you try to remove the disc using the controls, the carriage opens with the disc rotating on it.

Typical signs of good work are clearly visible phases:

start and acceleration of disk rotation;
steady-state rotation mode;
braking interval to a complete stop;
removal of the disc by the carriage tray and taking it out of the drive.

Reading head positioning servo system information provides a smooth approach of the head to the specified recording track with an error not exceeding half the track width in the search modes for the required piece of information and normal playback.

The movement of the read head, and with it the laser beam, along the disk field is carried out by the head motor. Engine operation is controlled by forward and reverse motion signals from the control processor, as well as signals from the radial error processor.

Typical signs of a malfunction are:

erratic movement of the head along the guides,
head immobility

Radial Tracking Servo System ensures the retention of the laser beam on the track and optimal conditions for reading information.

The system is based on the three-spot method. The essence of the method consists in dividing the main laser beam using a diffraction grating into three separate beams with a slight divergence.

The performance of the radial tracking system can be monitored by a change in the error signal supplied to the tracking drive.

Servo autofocus system provides precise focusing of the laser beam during operation on the working surface of the disc.

The operability of the focusing system can be judged both by the characteristic movements of the focal lens at the moment of starting the disk, and by the signal to start the disk acceleration mode when the focus of the laser beam is found.

Information reading system contains a photodetector array and differential signal amplifiers.

The normal operation of this system can be judged by the presence of high-frequency signals at its output when the disk rotates.

Laser diode control system provides the nominal excitation current of the diode in the modes of starting the disk and reading information.

A sign of normal system operation is the presence of an RF signal with an amplitude of about 1 V at the output of the readout system.

The third group of malfunctions includes all damage to the electronic filling of the GCD. Despite the rather small (relative to the total number of GCD defects) percentage of electronics failures - 5 ... 10%, troubleshooting electronic circuits is the most time-consuming part of the repair.

Typical GCD malfunctions and methods for their elimination
The following typical malfunctions of GCD components can be distinguished:
The computer does not identify the drive

CD loading / unloading mechanism does not work

GCD tests fail

The computer does not identify the gcd device, the drive access LED is off. First, check the correctness of the "Slave" jumper setting on the drive connector.

Then they check the serviceability of the EIDE cable interface and the correctness of its connection to the computer's motherboard.

Finally, check the correctness of the installation of the CD-ROM device in BIOS - Setup. If the drive still does not work after these checks, check the interface connector signals with an oscilloscope.

CD loading / unloading mechanism does not work

The disc drawer does not extend when you press the "Open" button and does not retract when you press the "Close" button

First, check the supply of +5 V voltage to the IC601 (disk drive system control processor) by pressing the "Open" key. In the presence of this voltage, check for the presence of control signals of the DZVD on the winding of the electric motor.

In the presence of control signals, the serviceability of the electric motor itself is checked: an external DC power source (9 V) is connected to the motor contacts. If the motor shaft starts to rotate quickly, it can be assumed that the motor is in good working order. If the motor does not rotate, rotates too slowly or heats up quickly, check the resistance of its windings with an ohmmeter: Ro6m = 6.5 Ohm. In case of significant (more than 30%) deviation of Ro6m from the specified value, replace the engine itself.

Mechanical breakdowns of parts of the transport mechanism are quite common.

Disc drawer does not open or close completely

First, the serviceability of the transport mechanism is checked, if necessary, it is cleaned of dust and dirt and lubricated with lithol or any viscous grease. Then check the actuation of the contact group ("three") when opening and closing the disc receiver (Figure 49). If necessary, this contact group is adjusted.
Figure 50 - General view of the contacts to control the operation of the disc receiver

The disc drawer spontaneously extends when power is applied to the drive

The disc receiver does not lock due to indistinct operation of the contact group ("three"). If necessary, this contact group is adjusted.

The information from the CD cannot be read or the reading is malfunctioning
The main reasons for these faults can be the following:

there is no disc rotation or the rotation speed differs from the nominal;
there is no LGS positioning;
there is no laser beam or its intensity is insufficient;
lack of drive sync signals;
the auto focusing system of the laser diode beam does not work;
malfunction of the + 5 or +12 B power supply circuits on the electronic board of the drive, or malfunction of a component on the board.

Insufficient laser beam intensity Symptom:

The drive after six months or a year of operation (as a rule, immediately after the expiration of the warranty period) stops reading CDs or DVDs. Usually the problem appears gradually.

Repair:

The problem is usually not related to contamination of the optical drive system. A dirty lens and a semitransparent mirror under it equally degrade the reading quality of both types of media. The reading head of the universal combo drives contains two laser modules. One of them is used for reading and writing DVD discs, the other for CD discs. Over time, the brightness of one of the lasers may decrease.

Small trimming resistors installed directly on the head regulate the current through the laser diode and by changing their value, the brightness of the laser radiation can be changed within certain limits. In the figure, they are circled and indicated by numbers 1 and 2.
Figure 51 - General view of the optical head. 1 and 2 laser diode current adjustment resistors

The generalized algorithm for troubleshooting GCD is presented in Figure 52

Figure 52 - Generalized algorithm for troubleshooting GCD

Transcript

1 TV repair - a technique for finding faults Finding a defect is much more difficult than fixing it, especially for a novice technician. The universal technique proposed by the author of the article will allow you to quickly and efficiently diagnose a modern TV. C WHAT TO START When repairing television receivers, there are situations when the television does not turn on and does not show any signs of life. This greatly complicates the localization of the defect, especially when you consider that it is often necessary to repair imported equipment without schematic diagrams. The foreman is faced with the task of identifying the malfunction and eliminating it with the least amount of time and effort. To do this, you must follow a specific troubleshooting technique. If a workshop or a private craftsman values their reputation, it is necessary to start by cleaning the apparatus. Armed with a soft brush and a vacuum cleaner, you should clean the inner surface of the case, the surface of the picture tube and the TV receiver board. After thorough cleaning, the board and the elements on it are visually inspected. Sometimes you can immediately determine the location of the malfunction by swollen or burst capacitors, by burnt resistors or by transistors and microcircuits that have burned through. It happens that after cleaning the kinescope from dust, instead of a transparent flask, we see a milky white inner surface (loss of vacuum). Much more often, visual inspection does not reveal external signs of defective parts. And then the question arises - where to start? POWER SUPPLY It is most advisable to start the repair with a check of the power supply. To do this, turn off the load (line scan output stage) and connect a 220 V, W incandescent lamp instead. eighteen

2 Typically, the line scan supply voltage is V, depending on the size of the picture tube. After examining the secondary circuits, on the board next to the pulse transformer of the power supply, we find the filter capacitor, which most often has a capacitance of microfarads and an operating voltage of about 160 V. Next to the filter there is a line scan supply voltage rectifier. After the filter, the voltage goes to the output stage through a choke, limiting resistor or fuse, and sometimes there is just a jumper on the board. Having soldered this element, we will disconnect the output stage of the power supply from the horizontal stage. In parallel with the capacitor, we connect an incandescent lamp - a load simulator. When you turn it on for the first time, the key transistor of the power supply may fail due to a malfunction of the piping elements. To prevent this from happening, it is better to turn on the power supply through another W incandescent lamp, used as a fuse and turned on instead of the soldered component. If there are faulty elements in the circuit and the current consumption is large, the lamp will light up, and all the voltage will drop across it. In such a situation, it is necessary, first of all, to check the input circuits, the mains rectifier, the filter capacitor and the powerful transistor of the power supply. If, when turned on, the lamp lit up and immediately went out or began to glow faintly, then we can assume that the power supply is working, and it is better to make further adjustments without a lamp. After turning on the power supply, measure the voltage across the load. Look carefully on the board for an output voltage adjustment resistor near the power supply. Usually there is an inscription next to it indicating the voltage value (V). If there are no such elements on the board, pay attention to the presence of breakpoints. Sometimes the value of the supply voltage is indicated next to the terminal of the primary winding of the line transformer. If the diagonal of the kinescope ", the voltage should be in the range of V, and with the size of the kinescope", the supply voltage range is usually V. If the supply voltage is higher than the specified values, it is necessary to check the integrity of the elements of the primary circuit of the power supply and the feedback circuit, which serves for installation and stabilization output voltage. Electrolytic capacitors should also be checked. When dry, their capacity decreases significantly, which leads to incorrect operation of the circuit and an increase in secondary voltages. For example, in the Akai CT2107D TV, when the electrolytic capacitor C911 (47 microfarads, 50 V) dries up, the voltage in the secondary circuit instead of 115 V may increase to 210 V. If the voltages are underestimated, it is necessary to check the secondary circuits for short circuits or large leaks, the integrity of the protection diodes R2K, R2M in the line scan supply circuit and the 33 V protection diodes in the vertical scan supply circuit. 2/8

3 For example, in the Gold Star CKT 2190 TV, with a faulty line-scan power filter capacitor of 33 microfarads, 160 V, which has a large leakage current, the output voltage instead of 115V was about 30 V. In the Funai TV-2000A MK7 TV, a protective diode R2M was broken, what led to the operation of the protection, and the TV did not turn on; in Funai TV-1400 MK10, a breakdown of a 33 V protective diode in the vertical scan power circuit also triggered the protection. LINE SCAN Having dealt with the power supply and making sure that it is in good working order, we restore the connection in the line scan power circuit, having removed the lamp that was used instead of the load. To turn on the TV for the first time, it is advisable to install an incandescent lamp used instead of a fuse. If the output stage of the horizontal scanning is working properly, the lamp will light up for a few seconds when turned on and will go out or will glow dimly. If, when turned on, the lamp flashed and continues to burn, you need to make sure that the horizontal output transistor is working properly. If the transistor is working properly, but there is no high voltage, make sure that there are control pulses at the base of the horizontal output transistor. If there are pulses and all voltages are normal, it can be assumed that the line transformer is faulty. Sometimes this is immediately clear from the strong heating of the latter, but it is very difficult to reliably say whether the TDKS is serviceable by external signs. In order to determine this exactly, you can use the following method. We apply rectangular pulses with a frequency of kHz of small amplitude to the collector winding of the transformer (you can use the oscilloscope calibration signal output]. We also connect the oscilloscope input there. With a working transformer, the maximum amplitude of the received differentiated pulses should not be less than the amplitude of the original rectangular pulses. we will see short differentiated pulses with an amplitude of two or more times less than the original rectangular. This method can also determine the malfunction of the transformers of network switching power supplies. The method also works without desoldering the transformer (of course, you need to make sure that there is no short circuit in the secondary circuits of the strapping). 3 / eight

4 Another line scan malfunction, in which the power supply does not turn on and the lamp turned on instead of the fuse glows brightly - breakdown of the line deflecting coils. This fault can be determined by disconnecting the coils. If the TV turns on normally after doing this, then the deflection system [OS] is probably faulty. To verify this, replace the deflection system with a known good one. In this case, the TV must be turned on for a very short time in order to avoid burn-through of the kinescope. Replacing the deflection system is not difficult. It is better to use an OS from a similar picture tube with a diagonal of the same size. The author had to install a deflection system from a Philips TV with a diagonal of 21 "in the Funai 2000 MKZ TV. After installing a new OS in the TV, it is necessary to adjust the convergence of the beams using a TV signal generator. the horizontal stripe is on, and if the frame scan is in good condition - the full raster.If there is no raster and a bright horizontal stripe is visible on the screen, adjust the accelerating voltage on the TDKS to reduce the brightness of the screen. you should look for a malfunction in the vertical scan. Diagnostics in the vertical scan unit should begin with checking the power supply of the master oscillator and the output stage. Most often, power is taken from the winding of the horizontal transformer. The supply voltage of these stages is V. The voltage is supplied through a limiting resistor, which and must be checked first. Frequent malfunctions in vertical scanning are breakdown or breakage of the rectifier diode and failure of the vertical scanning microcircuit. Rarely, but still there is an interturn short circuit in personnel deflecting coils. If you suspect a deflection system, it is better to check it by temporarily connecting a known good coil. Control should be carried out with an oscilloscope, observing the pulses directly on the frame coils. POWER SUPPLY CIRCUITS of the UNESCOPA It happens that the power supply unit and the scanner unit are in good working order, but the TV screen does not light up. In this case, you need to check the filament voltage, and if it is present, the integrity of the kinescope filament. In the author's practice, there were two cases when the filament winding of a line transformer was broken (Sony and Waltham TVs). Take your time to change the line transformer. To begin with, it should be carefully evaporated, cleaned of dust and carefully inspected the terminals of the filament winding. 4/8

5 Sometimes the break is near the lead under the epoxy layer. With a hot soldering iron, carefully remove a part of the resin and, if a break is found, we eliminate it, after which it is advisable to fill the place of repair with epoxy resin. If the break could not be found, you can wind the filament winding on the core of the same transformer. The number of turns is selected empirically (usually it is turns, wire MGTF 0.14]. The ends of the winding can be fixed with glue or mastic. . If there is no sound and image, the malfunction should be looked for in the radio channel (tuner and video processor). If there is sound and there is no image, the malfunction should be looked for in the video amplifier or color block. If there is an image and there is no sound, it is most likely that the video processor or low frequency amplifier is faulty. to check the power supply voltage of the radio channel, video and audio signals must be fed through the low-frequency input (you can use a TV signal generator or a regular video recorder). faulty sound channel, up to loudspeakers speakers and, if necessary, replace the defective element. If, after the signal was applied to the low-frequency input, the image and sound appeared, then the malfunction should be looked for in the previous stages. When checking the video processor, it is necessary to send the IF signal to the FSS input from the generator or from the tuner output of another TV. If the image and sound did not appear, we check the signal path with an oscilloscope and, if necessary, change the video processor (when replacing the microcircuit, it is better to immediately solder the socket). If there is an image and sound, then the malfunction should be looked for in the tuner or in its harness. First of all, you need to check if power is being supplied to the tuner. Check the integrity of the key transistors through which the voltage is supplied to the tuner when switching ranges. Track whether these 5/8

6 transistors signal from the control processor, check the magnitude and range of the tuning voltage, which should vary within V. When diagnosing tuner malfunctions, you need to send a signal from the antenna to the mixer, bypassing the RF amplifier stages. To do this, it is convenient to use a probe, which can be made from a disposable syringe with a removed plunger. An antenna socket should be installed in the upper part of the syringe and the central contact should be connected to the needle through the 470 pF capacitor. We bring the earth out with an ordinary wire; for convenience it is better to solder a crocodile clip to the earth wire. We connect the probe to the antenna plug and send a signal to the tuner stages. With the help of such a probe, it was possible to determine the malfunction in the tuner of the Grundig T OIRT TV. In this device, the first UHF stage was faulty. The malfunction was eliminated by feeding a signal through a 10 pF capacitor directly from the antenna socket, bypassing the first transistor, to the next tuner stage. The image quality and sensitivity of the TV after such a rework remained quite high and did not even affect the teletext operation. CONTROL UNIT It is especially necessary to dwell on the diagnostics of the TV control unit. When repairing it, it is advisable to use the diagram or reference data for the control processor. If you cannot find such data, you can try to download them from the website of the manufacturer of these components via the Internet (A malfunction in the unit may manifest itself as follows: the TV does not turn on, the TV does not respond to signals from the remote control or control buttons on the front panel, there are no volume and brightness controls , contrast, saturation and other parameters, there is no tuning for television programs, settings are not saved in memory, there is no indication of control parameters.If the TV does not turn on, first of all, we check the presence of power on the processor and the operation of the clock generator. control processor to the switching circuit.To do this, you need to find out the principle of turning on the TV. processo pe control, the turn-on signal is indicated by either Power or Stand-by. If a signal comes from the processor, then the fault should be looked for in the switching circuit, and if there is no signal, the processor will have to be changed. 6/8

7 If the TV turns on, but does not respond to signals from the remote control, you need to first check the remote control itself. You can check it on another TV of the same model. To test the consoles, you can make a simple device consisting of a photodiode connected to the CP-50 connector. The device is connected to an oscilloscope, the sensitivity of the oscilloscope is set within mV. The remote control should be aimed at the LED from a distance, see. Pulse bursts will be visible on the oscilloscope screen if the remote control is working properly. If there are no pulses, we diagnose the control panel. We check sequentially the power supply, the state of the contact tracks and the state of the contact pads on the control buttons, the presence of pulses at the output of the remote control microcircuit, the health of the transistor or transistors and the health of the emitting LEDs. Quartz resonator often fails after the remote control is dropped. If necessary, we change the faulty element or restore the contact pads and button coating (this can be done by applying graphite, for example, with a soft pencil, or by sticking a metallized film on the buttons). If the remote control is working properly, you need to trace the passage of the signal from the photodetector to the processor. If the signal reaches the processor, and nothing changes at its output, it can be assumed that the processor is faulty. If the TV is not controlled from the buttons on the front panel, you must first check the health of the buttons themselves, and then trace the presence of polling pulses and feed them to the control bus. If the TV is turned on from the remote control and the pulses are sent to the control bus, and the operational adjustments do not work, you need to find out with which output the microprocessor controls one or another adjustment (volume, brightness, contrast, saturation). Next, check the paths of these adjustments, right down to the actuators. The microprocessor generates control signals with a linearly varying duty cycle, and arriving at the actuators, these signals are converted into a linearly varying voltage. If the signal arrives at the actuator, and the device does not respond to this signal, then this device must be repaired, and if there is no control signal, the control processor must be replaced. If there is no tuning for television programs, we first check the sub-band selection node. Usually, through the buffers implemented on transistors, the processor supplies voltage to the tuner pins (0 or 12 V). It is these transistors that most often fail. But it happens that there are no signals from the processor 7/8

8 switching of sub-bands. In this case, you need to change the processor. Next, we check the tuning voltage generation unit. The supply voltage usually comes from a secondary rectifier from a line transformer and is V. From this voltage, V is formed with the help of a stabilizer. The microprocessor controls the switch, which forms the tuning voltage V using a signal with a ramping duty cycle, which, after the filters, is converted into a ramp voltage. Most often, stabilizer B fails. If the TV does not store the settings in memory, it is necessary, at any setting, to check the exchange of data between the control processor and the memory microcircuit via the CS, CLK, D1, DO buses. If there is an exchange, and the parameter values are not stored in the memory, replace the memory microcircuit. If there is no indication of control parameters on the TV, it is necessary in the indication mode to check the presence of bursts of video impulses of service information on the control processor along the R, G, B circuits and the brightness signal, as well as the passage of these signals through the buffers to the video amplifiers. In this article, we have touched on a small part of the faults that are found in television receivers. But in any case, the method of finding them will help you correctly identify and eliminate the malfunction and reduce the time spent on repairs. 8/8

GOLD STAR TV (LG) Model CF-20A80 1. Power supply malfunctions 1.1. When the TV is turned on, the mains fuse blows out The mains filter, rectifier, demagnetization unit is defective Disconnect

TV FUNAI Models 14 MK8, 20 MK8, 21 MK8 1. Power supply malfunctions 1.1. Mains fuse F601 blown Mains filter, rectifier, demagnetizing system defective - disconnect L601

FAULTS OF POWER SUPPLIES FOR FOREIGN COLOR TELEVISIONS Yu. Pavlov The power supply (IP) is one of the most important units in a color TV, which provides all its nodes with stabilized voltages

Download diagram of philips TV model 29pt840258 >>> Download diagram of philips TV model 29pt840258 Download diagram of philips TV model 29pt840258 After disconnecting input 9 TDA3566 recovered

STABILIZED POWER SOURCES IPS-1000-220 / 24V-25A IPS-1200-220 / 24V-35A IPS-1500-220 / 24V-50A IPS-950-220 / 48V-12A IPS-1200-220 / 48V-25A IPS- 1500-220 / 48V-30A IPS-950-220 / 60V-12A IPS-1200-220 / 60V-25A

POWER SUPPLIES IPS-1000-220 / 110V-10A IPS-1500-220 / 110V-15A IPS-1000-220 / 220V-5A IPS-1500-220 / 220V-7A DC (АС) / DC-1000-220 / 110V -10A (IPS-1000-220 / 110V-10A (DC / AC) / DC) DC (AC) / DC-1500-220 / 110V-15A (IPS-1500-220 / 110V-15A (DC / AC) / DC)

HEATING The device is intended for supplying household consumers with alternating current. Rated voltage 220 B, power consumption 1 kW. Applying other elements allows you to use the device

CONVERTER DC / DC-24 / 12V-20A DC / DC-24 / 48V-10A DC / DC-24 / 60V-10A Technical description CONTENTS 1. Purpose ... 3 2. Technical characteristics ... 3 3. Principle of operation ... 4 4. Safety measures ... 6 5. Connection

STABILIZED POWER SOURCES IPS-300-220 / 24V-10A IPS-300-220 / 48V-5A IPS-300-220 / 60V-5A DC / DC-220 / 24V-10A (IPS-300-220 / 24V-10A ( DC / AC) / DC)) DC / DC-220 / 48V-5A (IPS-300-220 / 48V-5A (DC / AC) / DC)) DC / DC-220 / 60B-5A

TELEPHONY REPAIR OF RADIO TELEPHONES Sanyo CLT-KM D. Sadchenkov The radiotelephone of the Sanyo CLT-KM series is a multi-channel radiotelephone (RT) with microprocessor control operating

Construction and repair of power supplies for digital STV receivers Attention! Use this copy for informational purposes only (burn after reading) Rip by Vasya Pupkin The power source is one

Laboratory work 6 Investigation of the local oscillator board of a professional receiver Purpose of work: 1. To get acquainted with the schematic diagram and constructive solution of the local oscillator board. 2. Remove the main characteristics

TROUBLESHOOTING 1.0 No power supply No raster Make sure that the power-saving circuit does not work Potential failure of the power-saving circuit Power supply Potential malfunction

UDC 62-799 I.A.KRITSANOV, undergraduate student (NI TPU) I. Yu. KRASNOV, Ph.D., associate professor, associate professor (NI TPU) Tomsk DEVICE FOR DIAGNOSTIC ELECTRICAL ELEMENTS Introduction In amateur radio practice it is often required

Inverter circuit pllm-m602a >>> Inverter circuit pllm-m602a Inverter circuit pllm-m602a It can be a transformer from a network adapter or something original. There is a counter-parallel source between the drain

STABILIZED POWER SOURCES IPS-1000-220 / 110V-10A-2U IPS-1500-220 / 110V-15A-2U IPS-2000-220 / 110V-20A-2U IPS-1000-220 / 220V-5A-2U IPS-1500 -220 / 220V-7A-2U IPS-2000-220 / 220V-10A-2U DC (AC) / DC-1000-220 / 110V-10A-2U

STABILIZED POWER SUPPLIES IPS-1000-220 / 24V-25A-2U (DC (AC) / DC-1000-220 / 24V-25A-2U) IPS-1200-220 / 24V-35A-2U (DC (AC) / DC) -1200-220 / 24V-35A-2U) IPS-1500-220 / 24V-50A-2U (DC (AC) / DC -1500-220 / 24V-50A-2U)

Sony kv m2100k channel setup without a remote control >>> Sony kv m2100k channel setup without a remote control Sony kv m2100k channel setup without a remote control I'm digging further and one more microcircuit is faulty - TDA4650. But,

As a rule, power supplies (PS) of a personal computer (PC) are built according to the scheme of a push-pull adjustable converter. This is due to the fact that a significant amount of power is required to power the computer's devices.

Ministry of Communications of the USSR Moscow Order of the Red Banner of Labor Electrotechnical Institute of Communications Department of Television Laboratory work 3 RESEARCH OF TRANSISTOR LINE SCAN GENERATOR

SECONDARY POWER SUPPLY RESERVED BBP-30 V.4 TS Technical data sheet Redundant secondary power supply with filtering from mutual influence of consumers on each channel

TV sets "SONY KV-M2540 B, D, E, K" and "SONY KV-M2541 A, D, E, K, L, U". Critical malfunctions I. Morozov, V. Strelchenko The method of detecting and eliminating critical malfunctions is considered

Funai tv-2000a mk8 turn on av without a remote control >>> Funai tv-2000a mk8 turn on av without a remote control Funai tv-2000a mk8 turn on av without a remote control Ring cracks form under it - laughter and tears of any TV master,

Reactive power inverter The device is designed to supply household consumers with alternating current. Rated voltage 220 V, power consumption 1-5 kW. The device can be used with any

Rainford TV faults >>> Rainford TV faults Rainford TV faults Troubleshooting Rainford TVs RAINFORD TV5182 Assembled on BEKO G80 chassis.

STABILIZED POWER SUPPLY ISS-500-220V / 220V-2A-D ISS-500-220V / 110V-4A-D ISS-500-220V / 60V-8A-D ISS-500-220V / 48V-10A-D ISS-500 -220V / 24V-15A-D AC (DC) / DC operation manual CONTENTS 1.

TROUBLESHOOTING AND TROUBLESHOOTING OF SONY TVs ASSEMBLED ON BE-4A CHASSIS I.Morozov Considered methods of troubleshooting popular models of SONY TVs with the size

Operation manual Redundant secondary power supply OPTIMUS 1220-RM-7 Redundant secondary power supply Optimus 1220-RM-7 ARGP.435520.003TU is intended for

Generator 20Hz 100 kHz 2kW Schemes 201g. Technical characteristics The generator is designed to operate on a resistive and / or inductive load and provides the following parameters: - output voltage 20

EU / A FEATURES w Push-pull output with pause between pulses w Frequency switching input w Compact housing w Minimum number of attachments w Low power consumption w Suitable for use

Testing the useful output using the FM circuitry. The same imported ferrite rings in plastic insulation with a permeability of 2000NM and a size of 22x38x8 mm were used as rings. 1. Setting up a push-pull

DS_en.qxd.0.0: 9 Page EU / A FEATURES Push-pull output with pause between pulses Frequency switching input Compact housing Minimum number of attachments Low power consumption Possibility

POWER SUPPLIES BPS-3000-380 / 24V-100A-14 BPS-3000-380 / 48V-60A-14 BPS-3000-380 / 60V-50A-14 BPS-3000-380 / 110V-25A-14 BPS-3000- 380 / 220V-15A-14 operation manual CONTENTS 1. Purpose ... 3 2. Technical

Diagram of the TV ruby 37m10 2 >>> Diagram of the TV ruby 37m10 2 Diagram of the TV ruby 37m10 2 The reason is the breakage of L102 along the 8v circuit at 39 feet TDA9381. All voltages are too low, there is no start. Power Supply

12! ATTENTION! THIS MANUAL IS INTENDED FOR HIGHLY QUALIFIED PROFESSIONALS. COMPLIANCE WITH ELEMENTARY SAFETY RULES AND CAREFULNESS WHEN REPAIRING THE WELDING EQUIPMENT WILL PROVIDE YOU

Schematic diagram sharp 14h sc >>>

Schematic diagram sharp 14h sc >>> Schematic diagram sharp 14h sc Schematic diagram sharp 14h sc It's good that a diagram is sometimes applied to them. In the course of the run, the personnel disappeared - it was cut short

Meter ESR + LCF v3.4 С / R / ESRa + LCFPmeter_V3.4 Author: miron63 [email protected] Appearance: Main purpose: Repair of electronic devices. The device described below measures: ESR of electrolytic

HELIKON 101 LOUDSPEAKER AMPLIFIER Technical description, operating instructions and passport AMPLIFIER "HELIKON 101" Operation manual and passport. BEFORE USING THE AMPLIFIER

Alteration of the ETALON ZX7-180R welder (Replacing the IGBT module with discrete elements) The DM2G100SH6A module used in this device costs from 3 to 6 thousand rubles, which is why if it fails

HELIKON - 100 LOUDSPEAKING COMMUNICATION AMPLIFIER Technical description, operating instructions and passport AMPLIFIER "HELIKON - 100" Operation manual and passport. BEFORE USING THE AMPLIFIER

INSTRUCTIONS FOR USE Amplifiers A-55 A-65 RA-125 Dear user, Congratulations on your purchase of an ONIX integrated amplifier. Be sure to read this manual before using

2.9 Control unit for primary circuits SB71 The unit is designed to generate control signals proportional to the effective value of the primary supply voltage and the voltage across the network capacitors

CJSC "NPF" Sibneftekart "Interphone loudspeaker PGU gas station" Client "Operation manual v.3. IE 66523-010-24630734-2006 Tomsk - 2013 1 CONTENTS Purpose ... 3 1 Technical data ...

GENERATOR CONTROL LAMP "What does the red battery light on my dashboard mean?" In general, this means that the voltage at the generator output

STABILIZED POWER SOURCES IPS-1000-220 / 24V-25A-2U IPS-1200-220 / 24V-35A-2U IPS-1500-220 / 24V-50A-2U IPS-2000-220 / 24V-70A-2U IPS-950 -220 / 48V-12A-2U IPS-1200-220 / 48V-25A-2U IPS-1500-220 / 48V-30A-2U

Trilight lantern for sports fans A. BUTSKIKH, Tomsk Having distributed a large number of such lanterns to the fans, it is possible to organize a light show in the stands during the competition, since the flashlights will

UNIFIED POWER SUPPLY MODULE UMP3 Instructions for setting up and testing TsAKT.436734.024 I1

DIGITAL MULTIMETER M-9502 Instruction Manual SAFETY INFORMATION Caution: Please read the instruction manual carefully before taking measurements. This measuring device

Technical description and operation manual LABORATORY OF HIGH-VOLTAGE POWER SUPPLIES AND PULSE GENERATORS Charger ZU10-60 ZU10-60 HVPSystems 1 Contents 1 Purpose of the device ...

GENERATOR The device is designed to rewind indications of induction electric meters without changing their connection schemes. With regard to electronic and electronic-mechanical meters, in the design of which

Stepper Motor Driver ADR810 / ADR812 OPERATING MANUAL April-2010 1 CONTENTS 1. PURPOSE OF THE DEVICE ... 3 2. TECHNICAL SPECIFICATIONS ... 3 3. CASE DRAWING ... 3 4. SUMMARY LIST

0073-1- 6284 26945 Universal - Central Dimmer 6593-102 STD-500MA - Power Amplifier 6594-102 STD-420SL Instruction Manual for qualified electricians only Fig. 1 Central

HELIKON 600 LOUDSPEAKER AMPLIFIER Technical description, operating instructions and passport AMPLIFIER "HELIKON 600" Operation manual and passport. BEFORE USING THE AMPLIFIER

SSC CERTIFICATE OS / 1-SP-1010 Uninterruptible Power Supply. UPS-01 unit. SM3.090.031 OM (rev. 1 / April 2009) SIMOS Perm CONTENTS Page 1. Purpose. 4 2. Technical data..5 3. Unit design..6

Install a new filter in its place so that the plastic tab is directed outward; snap in the filter holder; close the top cover of the printer. 4. Cleaning and maintenance of the inner surface

Task 1 Demonstration version of the qualifying stage Electronics grade 11 The ammeter is designed to measure the current I A = 2 A and has an internal resistance R A = 0.2 Ohm. Find the resistance of the shunt

Technical characteristics of one- and two-channel PA-600/720/1000 / 248DP power amplifiers Functional characteristics Model Power 600W Single-channel PA-720DP 720W PA-1000DP 1000W Dual-channel

POWER SUPPLY UNIT OF CONTROL UNIT BPBU-3P Instructions for setting up and checking TsAKT.436121.011 I1 This manual is intended for setting up by the manufacturer and checking by the quality control department (QC)

MY - 64 DIGITAL MULTIMETER INSTRUCTIONS FOR USE 1. CONDITIONS FOR SAFE USE AND STORAGE The device is designed in accordance with the IEC-1010 instruction concerning electronic measuring instruments.

DSO 062 Oscilloscope Assembly and Operating Instructions DSO 062 Oscilloscope Basic Controls and Modes Buttons Normal NORM Capture HOLD OK Capture To Normal Mode + - + (Hold) Fast

STABILIZED POWER SUPPLY ISS-500-220V / 24V-15A-D (AC (DC) / DC) IPS-500-220V / 48V-10A-D (AC (DC) / DC) IPS-500-220V / 60V-8A -D (AC (DC) / DC) IPS-500-220V / 110V-4A-D (AC (DC) / DC) IPS-500-220V / 220V-2A-D (AC (DC) / DC)

When finding a malfunction in the equipment, they use various methods and methods. There are the following troubleshooting methods:

1. Sequential element-by-element checks.

2. Group checks.

3. Combination.

The method of successive element-by-element checks consists in checking the elements of the system one by one in a certain sequence, predetermined.

As a result of testing each element, its state is established. If the checked item is healthy, then the next one in order is checked. (Can be tested sequentially along the signal path, or in another predetermined order). The detected faulty element is restored, then a comprehensive check of the equipment is carried out.

The method of group checks consists in the fact that by measuring one or several parameters, a group of elements is determined in which there are faults. Then another series of measurements is carried out, allowing you to select a subgroup of elements, including the faulty one.

As a result of a sequential series of checks, the area of the faulty part is gradually narrowed down until a specific faulty element is identified.

The combination method consists in the measurement of a certain set of parameters during the troubleshooting process. Based on the results of these measurements, the faulty element is determined. The analysis of the state of the system is carried out after a complete group of checks.

When applying any method of troubleshooting, several methods of checking the state of equipment (elements, assemblies, equipment) can be used:

The method of external inspection consists in inspecting blocks (nodes) in which a failure is assumed. At the same time, the main attention is paid to the state of electrical installation (insulation damage, breaks, short circuits, traces of breakdown, etc.), to the appearance of resistors, capacitors, transformers, to contact systems of switches, relays, etc.

The replacement method consists in the fact that individual elements of the system (blocks, removable parts), supposed to be faulty, are replaced with obviously workable ones. If, after replacement, normal operation is restored, then it is concluded that the replaced element is faulty.

The comparison method is used in cases where the technical documentation does not contain maps of voltages, resistances, etc. Then the mode of the checked elements during troubleshooting is compared with the mode of a working device of the same type.

The method of control switches and checks consists in the use of controls, measuring and indicator devices to determine a faulty path or unit by sequentially switching the equipment to various operating modes.

The method of intermediate measurements is used to check nodes, blocks, hardware elements that cannot be checked by other methods.

To check the condition at the control points of the equipment, voltages, frequencies and other signal parameters are measured. The measurement results are compared with the data in the technical documentation.

Repaired products are tested for compliance with the measurement of the main technical characteristics and bringing them (by means of adjustments) to the standards established by the technical specifications.

Sequence of operations for troubleshooting

Before proceeding with the repair, it is necessary to study well the schematic diagram of the equipment, the controls on its front panel and the method of testing the operability. It is also necessary to study the devices used in the repair.

All equipment malfunctions can be conditionally divided into three groups:

1. The hardware doesn't work at all. In such cases, the real probability of malfunction is embedded either in power supplies or in common equipment nodes. It is possible that the equipment does not work for one and, perhaps, a simple reason: a fuse has blown, an open or short circuit in the circuit, the electrolytic capacitor of the power filter has closed, etc. lead to failure of other parts and cause more complex malfunctions. A malfunction of this kind is simple in the sense that if it is detected and eliminated, the equipment will begin to work normally and will not require additional adjustments. The equipment does not always work due to the failure of single parts. There are times when replacing a defective part does not return it to normal operation and more complex adjustments are required.

2. The hardware is not fully functional. For example, only the transmit path or the receive path works. A malfunction can also be associated, as in the first case, with the failure of single parts and units of the faulty path.

3. The equipment works, but does not comply with the TU standards. For example, signal distortion, overestimation or understatement of levels. In such cases, it should be assumed that the mode of the transistors has changed, the parameters of radio components have changed, etc.

Therefore, it is necessary to seriously investigate the state of the equipment. This study may consist in measuring the power supply modes of transistors, taking a level diagram, etc.

The appearance of malfunctions in the equipment is possible when it is turned on or during operation. The basis for carrying out repairs in laboratory conditions is the first option, when for some reason (long-term storage, transportation, poor-quality preventive maintenance, etc.), several malfunctions may occur. The equipment located at each workplace has artificially introduced malfunctions. The causes of malfunctions, as a rule, are not determined by external examination. However, in general, troubleshooting should be carried out in the following sequence:

1. Carry out an external inspection in order to collect the first information about the symptoms of malfunctions and avoid wasting time searching for false malfunctions. During an external examination it is necessary:

make sure that the supply voltage is correctly supplied and the power switches are installed, that the connecting cables are securely connected, that the blocks are tightly inserted into the packages;

check the correct installation of switches, switch blocks, the integrity of the fuses.

If even when the equipment was turned on, signs of malfunctions appeared, then, first of all, the readings of the alarm and control devices should be analyzed. The information obtained is usually sufficient to determine where to look for a malfunction. Sound and optical signaling devices of the equipment are triggered in the following types of malfunctions:

loss of voltage at the outputs of power supplies and blown fuses;

malfunctions of the remote power supply system;

loss of currents of linear control frequencies and disruption of the normal operation of the AGC;

loss of carrier currents and control oscillations at the output of the generating equipment.

An external examination is also mandatory in the case when the malfunction is already identified before the block, node. In this case, an external examination determines burned-out parts, faulty installation, relay contacts and switches, the integrity of the rations, the absence of touches, the reliability of fastening, the operation of the MRU motor, etc.

The method of finding faults by external inspection is most effective in case of emergency faults (the appearance of smoke, a strong odor, arcing of contacts).

2. By checking the operability of the equipment, establish the faulty sections of the paths or the failure of individual packages or blocks.

3. By measuring the level diagram in the test sockets, determine the faulty unit, if it was not identified during the functional check. At this stage, it is sometimes advisable to use a replacement method, for example, replacing the unit with a known serviceable one from the spare parts package.

4. Having connected the faulty unit to the equipment with the help of repair hoses and measuring the levels at various points, determine the faulty unit. In this case, one should not always strive for high measurement accuracy. It is enough just to make sure of the presence or absence of a signal. When taking a level diagram, the first measurement point should be chosen so that it is possible to make sure that the measuring signal is supplied correctly to the input of the tested area. The point of each subsequent measurement must be selected so that the tested section is divided into two equally reliable parts in it, and so that the accessibility of connecting measuring instruments to the output of the node is ensured. This method takes less time to check.

5. Finding the damage in the unit should begin with an external inspection, then check the supply voltage in the operating mode, if necessary, check the serviceability of individual elements. In the absence of the necessary data on the operating modes of the node (in the operational documentation, the voltages on the transistor electrodes are not indicated for all nodes), it is advisable to use a method of comparison with the parameters of a known-good node or a method of replacement.

6. Replace the failed part with a serviceable one. After that, make control measurements in the unit that underwent repair, and then in the block. In some cases (for example, during the repair of amplifiers, PKK), the adjustment and fine-tuning of the repaired unit is carried out until it fully complies with the data in the operational documentation.

Topic 1.18. Installation work with cable. Preparing the cable for installation. Knitting a tourniquet.

Preparation of cables in plastic sheathing and with polyethylene insulation of cores is basically no different from preparing cables in lead sheathing. All types of checks (for tightness of the sheath, breakage and communication of the cores with the screen, breakage of the screen, insulation resistance of the cores) are performed in the same way as for cables in a lead sheath, but take into account that a bare copper core is used as the ground. After making sure that the sheaths and cores are in good condition, the cable is temporarily reinforced on the consoles with wire bands and proceeded to cutting.

The preparation of the cable for laying begins with the fact that the drums with the cable are transported along the highway in cars or special carts. If the route passes in the immediate vicinity of the railroad bed, the cable is transported on railway platforms, from which it is immediately laid into a trench. Before laying the cable in the ground, check the tightness of its sheath, the insulation resistance of the cores and the absence of short circuits and breaks in them.

To prepare the installation, you first need to fix both ends of the cable, either according to the shape of the well, if the splicing is done in the well, or in any form. Then, heat-shrinkable tubes must be installed on both ends of the cable, while the diameter of this tube should be slightly larger than the diameter of the cable. On top of the heat-shrinkable tubes, parts of a polyethylene sleeve are put on.

Next, it is necessary to fasten special clamps at both ends of the cable, designed to organize the shield bus of the cable. After fixing the clamps, clean the plastic sheath and the aluminum tape. The stripping length should be 15 mm at both ends. This length is chosen to result in a smooth coupling. Place the clips on the aluminum tape and use a screwdriver to fasten them to the end of the cable. Next, you need to connect both terminals with a temporary wire to provide a shield bus. Now you need to split the cable pairs into twigs and ring them. A dial-up is necessary to identify faults in the conductors. Breaking into twists helps in the future to quickly and most importantly twist both sections of the cable correctly.

To check the cable for "break" and "message", sections of the sheath with a length of 150 to 400 mm are removed from its ends, the belt insulation is cut off and removed from the core.

It is not recommended to trim the threads and ribbons that hold the bundles and strands together. At one end of the cable, insulation is removed from all cores in sections with a length of 20 to 25 mm, then the cores are collected in bundles of 10-50 pairs. All veins of each bundle are short-circuited, tightly wrapping their stripped sections with bare copper vein. All bundles are interconnected with one piece of stripped copper conductor. The bundle of bundles is connected to the shield or metal sheath of the cable.

An open check is performed at the opposite end of the cable. The wires of the handset (or headset) are connected in series with the battery and the screen (or metal sheath) of the cable. With a free wire from the tube, alternately touch each core of the cable (Figure 11.6). If a click is heard in the tube when touched, then the tested core is working properly. When you touch the broken core, there will be no click.

The veins being checked are not stripped. Contact is achieved due to the fact that when cutting the cable with a hacksaw or sector scissors, the ends of the cores protrude beyond the edge of the insulation.

For convenience, the free wire from the tube is connected with side cutters and the ends of the cores are touched with them. If necessary, the insulation of the tested core is cleaned or bite through.

Finding a faulty item takes a third of the repair time. Since the number of elements in objects of automation tools is large, direct enumeration of elements to assess their state is impossible. When performing work on troubleshooting, it is necessary to adhere to certain rules. Search technology can be broken down into the basic operations shown in Figure 3.1.

Figure 3.1 - Technology of search of failures (malfunctions)

The troubleshooting process is reduced to carrying out various checks and making a decision on the further development of the search based on the results of the check.

The troubleshooting process has two stages: selection of the sequence for checking the elements; selection of a method for conducting individual verification operations.

The search can be carried out according to a predetermined sequence of checks, or the progress of each subsequent check is determined by the result of the previous one. Depending on this, the following are distinguished verification methods:

- sequential element-wise;

- consecutive group;

Combinational.

The choice of the sequence of checks depends on the design of the products, and can change in the process of accumulating information on the reliability and laboriousness of checking the elements.

3.2.1 Sequential item-by-item test method consists in the fact that the elements of the products during troubleshooting are checked one by one in a certain, predetermined sequence. If the next item to be checked turned out to be functional, then proceed to checking the next item. If a faulty element is found, the search is terminated and the element is replaced (repaired). Then the object is checked for operability. If in this case the object (system) does not function normally, then proceed to further verification. Moreover, the check begins from the position at which the faulty element was found. When a second faulty element is found, it is also replaced or repaired (restored), and the object is again checked for operability. And so on until the object or system functions normally.

EXAMPLE The simplest example of using this method is troubleshooting in the automatic control system of one of the process parameters. The regulator is checked first, then the actuator, then the amplifier, etc. Thus, the object is established, the malfunction of which caused the disruption of the normal functioning of the automatic control system (Figure 3.2).

Figure 3.2 - Block diagram of an automatic control system of the "Crystal" type

If, for example, a malfunction in an actuator is detected, the element-by-element structure of this device is considered (Figure 3.3).

Figure 3.3 - Block diagram of the actuator

Here you can set the following sequence for checking items: 1-2-3-4-5-6-7-8. the most vulnerable of them may be elements 1, 2, 4, 7 and 8. Therefore, when using the element-by-element method of verification, there are two possible ways of ordering the control of elements.

When searching for a malfunction in a device, the object is first identified, the malfunction of which caused the malfunction of the device. Then, the element-by-element structure of the faulty device object is considered.

When using the element-by-element method, checks are possible two ways of ordering the control of elements.

1) If elements are used in the product, the duration of the check of which is approximately the same, then the check should be started with the elements with the least reliability.

2) If the reliability of the elements of a given product is approximately the same, then it is advisable to start checking with the element, which requires the least time to check.

For the successful use of these rules, it is necessary to know not only the functional and schematic diagrams of objects and systems, but to have a clear idea of the reliability of their elements.

Lack of method- a relatively large number of checks. This is explained by the fact that this method does not use functional connections of elements when searching, although this makes the method universal, since it does not depend on the functional diagram of the system.

3.2.2 Sequential Bulk Test Method consists in the fact that all the elements of the object, taking into account their functional connections, are divided into separate groups and the serviceability of each group as a whole is monitored. The sequence of the checks is determined by the result of the previous check. As the checks are carried out, the number of items to be checked decreases. At the last stage of control, there should be one element in the group.

An EXAMPLE of troubleshooting using this method is shown in the functional diagram of the system in Figure 3.4 of one of the types of ACS.

Figure 3.4 - An example of the structural diagram of the ACS

The scheme is divided into groups I-VIII. The structure is then split into two subgroups, etc. In this case, the sequence of checks will be as follows:

a) The signal at point 4 is monitored. If it is normal, then go to point 6, because it is assumed that the faulty element is in group V, VI, VII, VIII. If the signal at point 4 does not correspond to the norm, then the signal at point 2 is checked, since one of the elements I, II, III, IV is faulty. If the signal at point 2 is normal, then elements I, II are in good order, and point 3 should be checked. This reveals which of the elements III or IV is faulty.

b) If, when monitoring points 4 and 6, the signal meets the required parameters, then point 5 is monitored, as a result of which a faulty element V or VIII is determined.

With this method of troubleshooting, it is necessary to know the parameters of the signals at the test points.

If there are several faults in the object (system), then the fault finding scheme will not change. Moving along one of the branches of the structure, they inevitably come to one of the faulty elements. After elimination of this malfunction (restoration of the element), the operability of the object is checked. If there is a fault, the search process continues, which should lead to the second faulty element, etc.

This method is also called the midpoint method. However, in the general case, the number into which the structural diagram of the object (system) is divided may not be equal to two. It is necessary to break up the system, taking into account the functional connections of individual elements and the reliability of their work.

In the group method of checks, a distinction is made between checks “ with the exception" and " without exception”.

The check “with an exception” consists in the fact that the conclusion about the operability of one of the groups of elements is made on the basis of checking the other groups. For example, we have three groups of elements. According to the results of the check, the serviceability of groups 1 and 2 was established. Without checking, we conclude that the faulty element is in the 3rd group.

When checking "without exception", the performance of all groups is monitored. At the final stage, there is always a "no exception" check, which eliminates the possibility of error.

Dignity test sequences - significant reduction in troubleshooting time.

This method requires knowledge of the functional relationships of individual elements and their reliability.

3.2.3 The essence combinational method checks consists in the simultaneous measurement of several parameters. Based on the results of measurements of all parameters, a conclusion is made about the faulty element.

For the convenience of using this method, tables of the state of the monitored parameters are compiled. In this case, you should choose a block, a node, a sequential unbranched group of cascades as elements.

The first vertical column of the table indicates the elements of the structural diagram, and the first line - their parameters. The table is filled in according to the arrows in accordance with the following rules.

In turn, a malfunction is assumed only in this element. This malfunction leads to the output of the corresponding parameters out of tolerance. “0” is placed against these parameters in the table. If the specified malfunction does not affect any parameter, then a "1" is set against this parameter.

EXAMPLE In the block diagram (Figure 3.5) we measure the parameters A, B, C, D.

We assume that item 1 is faulty. Then, it is obvious that all parameters A, B, C and D will go out of tolerance. “0” is placed against these parameters in Table 3.2, i.e. the first row of the table will be all zeros. Then we assume that element 2 is faulty, while parameters A, B and C will not comply with the standards, and parameter D will be normal. The second line should be written "0001". Thus, they iterate over all the elements and analyze the state of the parameters. The same lines (7 and 8 of Table 3.2) indicate that this system does not distinguish between the parameters of faults of elements 7 and 8. In this case, the elements are combined into one or an additional parameter is introduced to distinguish them.

Figure 3.5 - To the use of the combination test method.

Table 3.2 - Graph of states

The elements	Options
A	V	WITH	D

To find a faulty element using such a table, proceed as follows. The operator writes the parameter values as a number, consisting of zeros and ones, according to the specified rule. To determine the faulty element, the resulting number is compared with the numbers in the table rows. Which row of the table coincides with the results of measuring the parameters, that element is faulty. If the result of measuring the parameters (numbers) does not match any row of the table, several elements are faulty.

Dignity this method has a relatively short troubleshooting time but is difficult to implement.

3.2.4 The sequence of the troubleshooting process is called search programs... A certain sequence of checks, which provides the minimum value of the mathematical expectation of the time of checks, is calculated by creating a mathematical model of the process of searching for a failed element.

The object in which the malfunction occurred consists of n elements. Element failures are independent. If any of the elements fails, the object fails. To control the health of the element, it is possible to apply a control signal to the input and check the response to this signal at the output. The failure rates of the elements are known q and the required time τ to check their serviceability. Determine the sequence of checks of the elements that provide the shortest troubleshooting time.

The optimal sequence should have the following property

, (3.1)

where τ is the average time for checking a serviceable element;

q is the conditional probability of failure of the element.

If the time for checking the health of all elements are equal, then the optimal sequence takes the form

q 1> q 2>…> q n -1. (3.2)

Those. control of the health of the element should be carried out in descending order of the conditional probability of failure of the elements.

Sequence (3.2) can be written in a more convenient form

λ 1> λ 2>…> λ n-1, (3.3)

The average time for troubleshooting the program is calculated by the formula

, (3.4)

where τ FROM. i - time spent on measurements in case of failure of the i-th element.

In turn

where τ R is the time spent on measurements at point R of the circuit;

r i is the number of measurements according to the program to detect the failure of the i-th element.

Taking into account (3.5)

, (3.6)

The order of building programs can be seen on examples.

Example 3.1

Figure 3.6 - Block diagram of A.

There is a diagram shown in Figure 3.6. The failure rate of elements: λ 1 = 0.1 h -1; λ 2 = 0.2 h -1; λ 3 = 0.2 h -1; λ 4 = 0.5 h -1. Measurement time at points of the circuit: τ 1 = 5 min; τ 2 = 8 minutes; τ 3 = 12 minutes; τ 4 = 18 min. It is required to draw up an optimal scheme for the troubleshooting program, provided that one of the elements of product A has failed.

The conditional probabilities of failures are determined. For the method of successive element-by-element checks, the conditional failure probabilities q correspond in value to λ. Then q 1 = 0.1; q 2 = 0.2; q 3 = 0.2; q 4 = 0.5. Determine the quotients: τ 1 / q 1 = 50; τ 2 / q 2 = 40; τ 3 / q 3 = 60; τ 4 / q 4 = 36;

According to (3.1), the first measurement must be made at the output of the fourth (IV) element. If the signal of the desired type is at the output of element IV, then the search should be continued and the next measurements should be made at the output of the second (II) element, etc.

For an analytical presentation of the troubleshooting process, as a rule, its graphic representation is used in the form of a troubleshooting program. The symbol of the element is made in the form of a rectangle, and the measurement is in the form of a circle inside with the numbers of the element, followed by the measurement. Then the troubleshooting program will be represented by a branching circuit consisting of circles with two outputs, denoting the measurement result (whether there is a desired signal or not - "yes" or "no") and ending with rectangles denoting the faulty element.

The search program for example 3.1 is shown in figure 3.7.

Figure 3.7 - Program for troubleshooting in product A

The average time for troubleshooting the program is calculated by the formula (3.6). Then:

Т ПН = q 1 (τ 4 + τ 2 + τ 1) + q 2 (τ 4 + τ 2) + q 3 (τ 4 + τ 2 + τ 1) + q 4 τ 4 = 0.1 (18 + 8 + 5) +0.2 (18 + 6) +0.2 (18 + 8 + 5) + 0.5 * 18 = 23.5 min.

Example 3.2.

There is a diagram shown in Figure 3.8. Failure rates of elements: λ 1 = 0.56 * 10 -4 h -1; λ 2 = 0.48 * 10 -4 h -1; λ 3 = 0.26 * 10 -4 h -1; λ 4 = 0.2 * 10 -4 h -1; λ 5 = 0.32 * 10 -4 h -1; λ 6 = 0.18 * 10 -4 h -1. The measurement time at all points is the same and is 2 minutes. It is required to draw up an optimal troubleshooting program, provided that one of the elements has failed.

Figure 3.8 - Block diagram of product B

To reduce the troubleshooting time, the sequential group check method is used, i.e. the measurement of the response to the control signal is made at a point in the circuit that divides the suspected faulty circuit in terms of probability (intensity) in half.

Hence, the conditional failure probability corresponds to the intensity value with a factor of 0.5 (half the value).

Then the conditional probabilities of failures: q 1 = 0.28; q 2 = 0.24; q 3 = 0.13; q 4 = 0.10; q 5 = 0.16; q 6 = 0.09.

The circuit consists of elements connected in series. You can use one control signal applied to the input of the first element. In this case, the first measurement must be made after the second element, because q 1 +; q 2 = 0.52, closest to dividing the circuit in terms of probability in half. If the required signal is not present after the second element, then it is concluded that the first or second element is faulty, and the measurement is performed after the first element. If there is a desired signal after the second element, then it is concluded that the right side of the circuit is faulty, which, in probability, is best divided in half at the measurement point after the fourth element, etc.

The troubleshooting program for this circuit is shown in Figure 3.9.

Figure 3.9 - Program for troubleshooting in product B.

Average time of troubleshooting according to the program:

T. P.N. = 0.28 (2 + 2) +0.24 (2 + 2) +0.13 (2 + 2 + 2) +0.20 (2 + 2 + 2) +0.16 (2 + 2 + 2 ) +0.9 (2 + 2 + 2) = 5.56 min.

3.2.5 When troubleshooting, in addition to choosing a method and program for troubleshooting an object (system), it is necessary to select a method (methods) for checking the health of individual elements. The most common methods of checking the health of elements:

Visual inspection;

Control switches and adjustments;

Intermediate measurements;

Comparison;

Typical malfunctions;

Isolation of a block or cascade, node;

Test - signals.

Visual inspection usually involves the use of sight and hearing. They allow you to monitor the state of installation of the CA, cables, individual elements, printed circuit boards, etc., as well as check the operation of a number of units, less often by ear.

Advantage this kind of checks in simplicity.

Flaw- the ability to identify a faulty element is limited. A malfunction can be determined only with clearly pronounced external signs: a change in the color of an element under the influence of temperature, sparking, the appearance of smoke and odor from burning wire insulation, etc. Such signs are rare. In addition, in practice, interdependent failures are often encountered, therefore, even if a faulty element is found by external inspection, additional checks must be carried out to identify the true causes of the failure (for example, when a fuse fails, a blown thread of which is visible "by eye").

Method of control switches and adjustments requires an assessment of external signs of malfunctions by analyzing circuits and using switching devices, adjustments, monitoring (signal lights, built-in devices, circuit breakers, etc.). In this case, a faulty node, block or path of the object (system) circuit is determined, i.e. a set of elements that perform a specific function of the object (conversion, indicator blocks, protection or switching unit, transmission path, etc.).

Dignity method in the speed and simplicity of testing the assumptions about the state of the sections of the object's circuit.

Flaw- limitedness, because allows you to identify areas, and not a specific location of damage.

Intermediate measurement method is the most common and basic for electrical and electronic devices. The parameters of a system, block, unit or element are determined using a hand-held portable or automated built-in control and measuring equipment (KIA) or special measuring devices, automatic control systems.

In this case, power modes, parameters of communication lines are measured, measurements are taken at control points. The speed of troubleshooting is to a large extent ensured by the ability of the service personnel to correctly take measurements. The obtained parameter values are compared with their values from the technical documentation, with the tables of the modes of this product.

Replacement method consists in the fact that instead of an element suspected of a malfunction (node, block, etc.), a similar, obviously serviceable element is installed. After replacement, the object (system) is checked for functioning. If the parameters of the system are within the normal range, then it is concluded that the replaced element is faulty. The advantage of this method is simplicity. But in practice, this method has limitations, firstly, due to the lack of spare elements, and secondly, due to the need for adjustments due to insufficient interchangeability.

Dependent failures can lead to the failure of a newly installed element, therefore this type of check is used when the suspect element is easily removable and inexpensive.

Comparison method - the mode of a faulty section (node, block) of an object or system is compared with the mode of a single-type section of a working object. The advantage of the method is the absence of the need for knowledge of absolute values, measured values and parameters. At the same time, this method allows you to identify rather complex malfunctions. The disadvantage of this method is the need for a spare (bench) set of equipment and, as a consequence, the possibility of using this method only in a laboratory.

At way of typical malfunctions failure is sought based on known characteristics. Such malfunctions and their symptoms are presented in the form of tables in the CA operating instructions.

Tables of typical faults have a number of disadvantages, of which the following are most significant:

The tables do not provide an unambiguous connection between the signs of failure and possible malfunctions: several different malfunctions are tied to one symptom and usually without any indication of the peculiarities of their occurrence;

The tables often lack instructions on how to carry out tests aimed at clarifying the cause of failures. A separate external sign cannot indicate a specific reason for the failure, and to find it, a logical comparison of a number of external signs is necessary, including the readings of control devices and test results;

The failure search actions recommended by the tables do not contain causal relationships and are not distributed in the order of their sequence, while the actual search is a clear sequence of various checks (tests).

Test signals are widely used in various computers, in calculating devices. During this test, a signal with certain characteristics is applied to the input of the monitored device. Analysis of the output signal allows you to determine the location of the faulty element.

Block isolation(node, site, cascade) justified by the fact that in some cases a block or cascade is connected by a large number of functional connections with other parts of the object. If such a unit fails, it is difficult to determine where the malfunction occurred - in the unit itself or in functionally related parts of the product. Disconnection of some functional links sometimes allows localizing the location of the faulty element.

Each of the considered private methods of troubleshooting has significant limitations, therefore, in the practice of repairing instrumentation and automation systems, several private methods are usually used together. This combination of methods allows you to reduce the overall search time and thereby contributes to its success.

A device for finding faults in circuits. Repair of TVs - a technique for finding faults

Basic concepts of troubleshooting.

Method description schema:

1. Clarification of the history of the occurrence of the malfunction.

2. External examination.

3. Ringing.

4. Removal of performance characteristics

5. Observation of the passage of signals through the cascades.

6.Comparison with a good unit.

7. Modeling.

8.Division into functional blocks.

9. Temporary modification of the circuit.

10. Inclusion of the functional block outside the system, in conditions that simulate the system.

11.Preliminary check of functional blocks.

12. Replacement method.

13. Checking the operating mode of the element.

14. Provocative impact.

15. Checking the temperature of the element.

16. Execution of test programs.

17. Step-by-step execution of commands.

18. Test signatures.

19. "Exit to the entrance".

20. Typical malfunctions.

21. Analysis of the impact of the malfunction.

22. Peripheral scanning.

3.1.1. Features of a typical PC power supply circuit. The main criteria for diagnosing power supplies.

3.1.2. Malfunctions of power supplies, their symptoms, causes and remedies

3.1.3. Algorithms for finding malfunctions of the PC power supply

3.1.4. The main malfunctions of the motherboard, their symptoms, causes and remedies

4.1.4.1 Main elements of the motherboard

3.1.4.2. System board malfunctions, their symptoms, causes and remedies

3.1.5 Malfunctions of the power supply unit of the CPU, their symptoms and remedies

3.1.6. Features of the design of modern hard disk drives, types of defects in the magnetic disk of hard disk drives

3.1.7. Hardware malfunctions of hard disk drives, their nature of manifestation, methods of their elimination

3.1.8. HDD file system malfunctions and methods of their elimination

3.1.9. Typical OS malfunctions, an algorithm for their search and elimination

3.1.10 Malfunctions of the flotation device, their nature of manifestation, the method of their elimination

3.1.11 GCD malfunctions, their nature of manifestation, methods of their elimination

Transcript

Password recovery