Universal acceleration of the tester multimeter. ICL7106 chips, ICL7106R, ICL7106S - ADC (characteristics, datasheet) Datashitte on a microcircuit T 7106

Reference data for microcircuits analog-to-digital converters ICL7106, ICL7106R, ICL7106S, COFOVKA, technical parameters, typical inclusion scheme. The ICL7106 microcircuit is an ADC with an output by a 3.5 discharge liquid crystal digital indicator. It is used in measuring instruments.

ICL7106 is available in three embodiments of the enclosures: ICL7106 - PDIP-40, ICL7106R - PDIP-40 (with mirror layout of outputs), and ICL7106S in the MQFP housing (with a four-sided positioning). As well as in the inappropsy version.

Characteristics of microcircuits

Electrical parameters:

1. The maximum allowable supply voltage that does not lead to damage \u003d 15V.
2. Nominal supply voltage \u003d 9V.
3. Current consumption nominal \u003d 1m.
4. Current current no more \u003d 1.8 mA.
5. Number of discharges indication \u003d 3.5
6. Permanent voltage at the input relative to the minus power supply \u003d sv.
7. Scale \u003d 2V or 200MV.
8. The temperature drift of zero is no more \u003d 1 UV / s.
9. Noise at VVx \u003d 0, 200 mV scale is no more \u003d 15 UV.

Purpose of the conclusions of the microcircuit

Fig. 1. Calp ICL7106S chip.

Fig. 2. Cocoles and the location of the conclusions for the ICL7106 chip, ICL7106R.

Typical inclusion scheme

The clock frequency is set by the RC chain on the outputs 38.39, 40 (or 1,2,3 for a mirror layout). FOSC \u003d 0.45 / (RC). Capacity should be at least 50 PF, resistance of at least 50 com. Typical frequency FOSC \u003d 48 kHz.

The clock frequency is 4 times lower than FOSC.

C1 \u003d 0.1 μF C2 \u003d 0.47 μF SZ \u003d 0.22 μF C4 \u003d 100 PF R2 \u003d 47 kΩ R3 \u003d 100 com R5 \u003d 1 MΩ.

For the scale 0-199.0MV R1 \u003d 24 com R4 \u003d 1 com.

For a scale 0-1.9999 R1 \u003d 24 com R4 \u003d 25 com.

Fig. 3. Typical circuit for switching on the ICL7106 microcircuit.

Fig. 4. Equivalent diagram of the ICL7106 ADC microcircuit.

It is impossible to introduce the desktop desktop without a convenient inexpensive digital multimeter. This article discusses the digital multimeter device of the 830th series, the most common faults and how to eliminate them.

Currently, a huge variety of digital measuring devices of varying degrees of complexity, reliability and quality are issued. The basis of all modern digital multimeters is the integral analog-digital voltage converter (ADC). One of the first such ADCs suitable for building inexpensive portable measuring instruments was the converter on the ICL71O6 chip released by Maxim. As a result, several successful inexpensive models of digital multimeters of the 830th series were developed, such as M830B, M830, M832, M838. Instead of the letter m can stand DT. Currently, this series of instruments is the most common and repetitive in the world. Its basic features: measuring constant and variable voltages up to 1000 V (input resistance of 1 MΩ), measurement of constant currents up to 10 A, measurement of resistance up to 2 MΩ, testing of diodes and transistors. In addition, in some models there is a sound ring mode of compounds, temperature measurements with a thermocouple and without thermocouple, meander generating a frequency of 50 ... 60 Hz or 1 kHz. The main manufacturer of the multimeters of this series is Precision Mastech Enterprises (Hong Kong).

Diagram and device work

Fig. 1. Structural diagram ADC 7106

The basis of the multimeter - the ADC IC1 type 7106 (the nearest domestic analog is chip 572fv5). Its structural diagram is shown in Fig. 1, and the basement for execution in the DIP-40 case - in Fig. 2. Before the kernel 7106 can be different prefixes depending on the manufacturer: ICL7106, TC7106, etc. Recently, inconspicuous chips (DIE CHIPS) are increasingly used, whose crystal is soldered directly to the printed circuit board.

Fig. 2. COCOLOGY ADC 7106 in the DIP-40 case

Consider the Mastech M832 multimeter scheme (Fig. 3). At the output 1 of IC1, a positive supply voltage of the 9V battery supply is supplied to the output 26 - negative. Inside the ADC there is a source of a stabilized voltage of 3 V, its input is connected to the output 1 IC1, and the output with the output 32. The output 32 is connected to the overall derivation of the multimeter and is galvanically associated with the input of SOM device. The voltage difference between the terminals 1 and 32 is approximately 3 V in a wide range of supply voltages - from nominal to 6.5 V. This stabilized voltage is fed to the adjustable divider R11, VR1, R13, the speaker of its output - it is the input of the chip 36 (in measurement mode Current and voltages). The divider is given by the potential U of the UG at the output 36 equal to 100 mV. Resistors R12, R25 and R26 perform protective functions. The Q102 transistor and resistors R109, R110NR111 are responsible for indicating the battery discharge. Capacitors C7, C8 and resistors R19, R20 are responsible for displaying decimal dispersion points.

Fig. 3. Multimeter M832 Multimeter Scheme

The range of working input voltages Umax directly depends on the level of adjustable reference voltage at the outputs 36 and 35 and is:

The stability and accuracy of the display indications depend on the stability of this reference voltage. The display indications N depend on the input voltage UBX and are expressed by the number:

Consider the operation of the device in the basic modes.

Voltage measurement

Simplified multimeter scheme in voltage measurement mode is shown in Fig. 4. When measuring the constant voltage, the input signal is fed to R1 ... R6, from the output of which via switch (according to 1-8 / 1 ... 1-8 / 2) is fed to a protective resistor R17. This resistor, in addition, when measuring the alternating voltage, together with the capacitor, forms the low-pass filter. Next, the signal comes to direct input of the ADC chip, output 31. The inverse input of the chip is supplied to the general output potential generated by the source of the stabilized voltage 3 V, the output 32.

Fig. 4. Simplified multimeter scheme in voltage measurement mode

When measuring alternating voltage, it is straightened by a single-alpapid rectifier on diode D1. Resistors R1 and R2 are selected in such a way that when measuring the sinusoidal voltage, the device showed the correct value. The protection of the ADC is provided by the R1 ... R6 divider and the R17 resistor.

Measurement of current

Fig. 5. Simplified multimeter scheme in current measurement mode

The simplified multimeter scheme in the current measurement mode is represented in Fig. 5. In the DC measurement mode, the latter flows through the RO, R8, R7 and R6 resistors, switched depending on the measurement range. The voltage drop on these resistors through R17 is fed to the ADC input, and the result is displayed on the display. The ADC protection is provided by diodes D2, D3 (in some models may not be installed) and Fuse F.

Measuring resistance

Fig. 6. Simplified multimeter scheme in resistance measurement mode

The simplified multimeter scheme in the resistance measurement mode is presented in Fig. 6. In resistance measurement mode, the dependence expressed by formula (2) is used. The diagram shows that the same current from the voltage source + LJ proceeds through the Ron reference resistor and the measured Rx resistor (input currents 35, 36, 30 and 31 are negligible) and the ratio of UBX and Uon is equal to the resistance ratio of RX resistors and Ron. R1 ....R6 is used as reference resistors, R10 and R103 are used as current-folding. The ADC protection is provided by the R18 thermistor [In some cheap models, conventional resistors are used with a rating of 1 ... 2 com), the transistor Q1 in Stabitron mode (not always) and resistors R35, R16 and R17 at the inputs 36, 35 and 31 ADC.

Problem mode

The call scheme uses the IC2 chip (LM358) containing two operating amplifiers. On one amplifier, the sound generator is assembled, on the other - a comparator. At the voltage at the input of the comparator (output 6), less threshold, at its output (output 7), a low voltage opens the key on the transistor Q101, resulting in a beep. The threshold is determined by the R103, R104 divider. Protection is provided by the R106 resistor at the input of the comparator.

Defects Multimeters

All faults can be divided into factory marriage (and it happens) and damage caused by erroneous actions of the operator.

Since multimetting is used in multimeters, it is possible to closes the elements, bad solders and breakdowns of elements, especially located along the edges of the board. Repair of a faulty instrument should be started with a visual inspection of the printed circuit board. The most common factory defects M832 multimeters are shown in the table.

The serviceability of the LCD display can be checked using the source of the variable voltage of the frequency of 50 ... 60 Hz and amplitude in several volts. As such a source of alternating voltage, you can take the M832 multimeter, which has a meander generation mode. To check the display, it is necessary to put it on a flat surface with the display upward, connect one short-screen M832 multimeter to the overall display of the indicator (lower row, left output), and the other multimeter probe is applied alternately to the rest of the display. If you manage to get the ignition of all the display segments, it means that it is working.

The faults described above may also appear during operation. It should be noted that in the mode of measuring constant voltage, the device rarely fails, because Well protected from overloads at the entrance. The main problems occur when measuring current or resistance.

Repair of a faulty instrument should be started from checking the supply voltage and health capacity of the ADC: stabilization voltage 3 V and lack of breakdown between power supply and total ADC output.

In the current measurement mode using the inputs V, Ω and MA, despite the presence of a fuse, there are cases when the fuse burns later than the safety diodes d2 or d3 have time to break through. If a fuse is installed in the multimeter, a fuse that does not correspond to the requirements of the instruction, then in this case the resistance of the R5 ... R8 is possible, and it can not be displayed visually on the resistances. In the first case, when only a diode makes itself, the defect manifests itself only in the current measurement mode: current through the device flows, but the display shows zeros. In case of burnout R5 or R6 resistors in voltage measurement mode, the instrument will oversee readings or show overload. With the full combustion of one or both resistors, the device is not reset in the voltage measurement mode, but when the inputs are closed, the display is set to zero. When combustion of R7 or R8 resistors on a current measurement ranges of 20 mA and 200 mA, the device will show overload, and in the range of 10 A - only zeros.

In the measurement mode of damage resistance occurs, as a rule, in the ranges of 200 Ohm and 2000 Ohm. In this case, when the voltage is applied to the input, the resistors R5, R6, R10, R18 can be burned, the transistor Q1 and the Sat condenser is made. If the transistor Q1 is completely broken, then when measuring the resistance, the device will show zeros. In case of incomplete test of the transistor, the multimeter with open arrows will show the resistance of this transistor. In voltage measurement and current modes, the transistor closes the switch switch and the multimeter readings do not affect. When the C6 capacitor test, the multimeter will not measure the voltage in the ranges of 20 V, 200 V and 1000 V or significantly underestimated the testimony in these ranges.

In the absence of an indication on the display in the presence of nutrition on the ADC or visually noticeable burnout of a large number of circuit elements, there is a high probability of damage to the ADC. The health of the ADC is checked by the voltage control of the source of the stabilized voltage of 3 V. In practice, the ADC flashes only when the high voltage is submitted to the input, much higher than 220 V. The cracks appear in the compound, the current of the microcircuit consumption increases, which leads to its noticeable heating. .

When a very high voltage is applied to the input of a very high voltage in the voltage measurement mode, a breakdown may occur by elements (resistors) and by printed circuit board, in the case of a voltage measurement mode, the diagram is protected by a divider on the resistances R1 ... R6.

In cheap models of the DT series, the long conclusions of parts can be condensed to the screen located on the back cover of the device, disrupting the operation of the scheme. Mastech has such defects are not observed.

The source of the stabilized voltage 3 V in the ADC in cheap Chinese models may in practice give a voltage of 2.6 ... 3.4 V, and some devices stop working at a voltage of the supply battery 8.5 V.

In DT models, low-quality ADCs are used, they are very sensitive to the rates of the C4 and R14 integrator chain. In Mastech multimeters, high-quality ADCs allow the use of elements of close nominal denominations.

Often in DT multimeters when the applicants are open in the resistance measurement mode, the device fits a long time to the overload value ("1" on the display) or not set at all. "Cerencing" a poor-quality chip of the ADC can be reduced R14 resistance rates with 300 to 100 com.

When measuring the resistance at the top of the range, the device "fills" readings, for example, when measuring the resistor resistance, 19.8 com shows 19.3 com. "Current" by replacing C4 capacitor on a capacitor of 0.22 ... 0.27 μF.

Since cheap Chinese firms use low-quality inapproprous ADCs, then there are no discontinuity break cases, and it can be very difficult to determine the cause of the fault, and it can differ in different ways, depending on the torn output. For example, one of the indicator conclusions does not burn. Since multimeters use displays with a static display, to determine the cause of the fault, it is necessary to check the voltage at the corresponding output of the ADC chip, it should be about 0.5 V relative to the overall output. If it is zero, then the ADC is defective.

An effective way to find the cause of the malfunction is the transversion of the analog-digital converter chip converter as follows. It is used one more, of course, a good, digital multimeter. It is included in the mode of checking diodes. Black dipstick, as usual, is installed in the soma, and the red into the VQMA jack. The red probe device is connected to the conclusion 26 [minus power supply), and black alternately concerns each leg of the ADC chip. Since protective diodes are installed on the inputs of an analog-digital converter in reverse turning on, then with such a connection, they should open, which will be reflected on the display as a voltage drop on the open diode. The real value of this voltage on the display will be somewhat larger, because The scheme includes resistors. Similarly, all the conclusions of the ADC are checked when the black probe is connected to the conclusion 1 [ADC power) and alternately touch the remaining conclusions of the microcircuit. The instrument readings must be similar. But if you change the polarity of inclusion with these checks on the opposite, the device should always show a break, because The input resistance of a good chip is very large. Thus, the conclusions can be considered defective, which show the final resistance at any polarity of the connection to the chip. If the device shows a cluster for any connection of the output under study, this is ninety percent talking about the inner break. The specified method of checking is quite universal and can be used when checking various digital and analog microcircuits.

There are malfunctions associated with poor-quality contacts on a gallery switch, the device only works when the gallets is pressed. Firms that produce cheap multimeters rarely cover the tracks under the lubricant's gallery switch, which they are quickly oxidized. Often the tracks are somewhat polluted. Repaired as follows: The printed circuit board is removed from the housing, and the switch paths are cleaned with alcohol. Then the thin layer of technical vaseline is applied. All, the device is fixed.

The instruments of the DT series sometimes happens that the alternating voltage is measured with a minus sign. This indicates incorrect installation D1, usually due to improper marking on the diode housing.

It happens that manufacturers of cheap multimeters put low-quality operational amplifiers in the circuit of the sound generator, and then when the device is turned on, the buzzer buzzes. This defect is eliminated by the electrolytic capacitor with a rating of 5 μF in parallel to the power chain. If this does not provide a steady operation of the sound generator, it is necessary to replace the operational amplifier on LM358P.

Often there is such a nuisance as battery leakage. Small drops of electrolyte can be wiped with alcohol, but if the fee flooded strongly, then good results can be obtained by flushing it with hot water with a household soap. After removing the indicator and disappearing a squeeze, using a brush, such as tooth, you need to thoroughly clean the board on both sides and rinse under the jet of water from the tap. Repeating washing 2 ... 3 times, the fee is dried and installed in the case.

In most devices produced recently, adversary (DIE CHIPS) ADCs are applied. The crystal is installed directly on the printed circuit board and is poured by a resin. Unfortunately, this significantly reduces the maintainability of the instruments, because When leaving the ADC, it is often found quite often, it is difficult to replace it. Instruments with inapproprous ADC are sometimes sensitive to bright light. For example, when working next to the desktop lamp, measurement errors may increase. The fact is that the instrument indicator and fee have some transparency, and the light, penetrating them, falls on the CRP crystal, causing a photo effect. To eliminate this disadvantage, you need to remove the board and, removing the indicator, take the location of the ADC crystal (it is clearly visible through the fee) with tight paper.

When you buy multimeters DT, you should pay attention to the quality of the switch mechanics, it is necessary to scroll the Multimeter's gallery switch several times to make sure that the switch is clearly and without hots: plastic defects are not repaired.

It is impossible to introduce the desktop desktop without a convenient inexpensive digital multimeter.

This article discusses the device of digital multimeters of the 830th series, its scheme, as well as the most common faults and how to eliminate them.

Currently, a huge variety of digital measuring devices of varying degrees of complexity, reliability and quality are issued. The basis of all modern digital multimeters is the integral analog-digital voltage converter (ADC). One of the first such ADCs suitable for building inexpensive portable measuring instruments was the converter on the ICL7106 chip released by Maxim. As a result, several successful inexpensive models of digital multimeters of the 830th series were developed, such as M830B, M830, M832, M838. Instead of the letter M can stand DT. Currently, this series of instruments is the most common and repetitive in the world. Its basic features: measuring constant and variable voltages up to 1000 V (input resistance of 1 MΩ), measurement of constant currents up to 10 A, measurement of resistance up to 2 MΩ, testing of diodes and transistors. In addition, in some models there is a sound ring mode of compounds, temperature measurements with a thermocouple and without thermocouple, meander generating a frequency of 50 ... 60 Hz or 1 kHz. The main manufacturer of the multimeters of this series is Precision Mastech Enterprises (Hong Kong).

Diagram and device work

Schematic diagram of multimeter

The basis of the multimeter - the ADC IC1 type 7106 (the nearest domestic analog is chip 572fv5). Its structural diagram is shown in Fig. 1, and the basement for execution in the DIP-40 case - in Fig. 2. Before the kernel 7106 can be different prefixes depending on the manufacturer: ICL7106, TC7106, etc. Recently, inconspicuous chips (DIE CHIPS) are increasingly used, whose crystal is soldered directly to the printed circuit board.

Consider the Mastech M832 multimeter scheme (Fig. 3). At the output 1 of IC1, a positive supply voltage of the 9V battery supply is supplied to the output 26 - negative. Inside the ADC, the source of the stabilized voltage is 3 V, its input is connected to the output 1 IC1, and the output with the output 32. The output 32 is connected to the overall output of the multi-meter and is galvanically connected to the input of the COM of the device. The difference of stresses between terminals 1 and 32 is approximately 3 V in a wide range of supply voltages - from nominal to 6.5 V. This stabilized voltage is fed to the adjustable divider R11, VR1, R13, and from its output, the input of the chip 36 (in mode Measurements of currents and voltages). The divider is set by the potential U at the output 36 equal to 100 mV. Resistors R12, R25 and R26 perform protective functions. The Q102 transistor and resistors R109, R110 and R111 are responsible for indicating the discharge of the battery. Capacitors C7, C8 and R19 resistors, R20 are responsible for displaying decimal dispersion points.

The range of operating input voltages U Max directly depends on the level of adjustable reference voltage at the outputs 36 and 35 and is

The stability and accuracy of the display indications depend on the stability of this reference voltage.

Display indications N depend on the input voltage U and are expressed by the number

Consider the operation of the device in the basic modes.

Voltage measurement

Simplified multimeter scheme in voltage measurement mode is shown in Fig. four.

When measuring the constant voltage, the input signal is fed to R1 ... R6, from the output of which through the switch [according to 1-8 / 1 ... 1-8 / 2) is fed to a protective resistor R17. This resistor, in addition, when measuring the alternating voltage, together with the C3 condenser, forms the low-pass filter. Next, the signal comes to direct input of the ADC chip, output 31. The inverse input of the chip is supplied to the general output potential generated by the source of the stabilized voltage 3 V, the output 32.

When measuring alternating voltage, it is straightened by a single-alpapid rectifier on diode D1. Resistors R1 and R2 are selected in such a way that when measuring the sinusoidal voltage, the device showed the correct value. The protection of the ADC is provided by the R1 ... R6 divider and the R17 resistor.

Measurement of current

The simplified multimeter scheme in the current measurement mode is represented in Fig. five.

In the DC measurement mode, the latter flows through resistors R0, R8, R7 and R6, switched depending on the measurement range. The voltage drop on these resistors through R17 is fed to the ADC input, and the result is displayed on the display. The ADC protection is provided by diodes D2, D3 (in some models may not be installed) and Fuse F.

Measuring resistance

The simplified multimeter scheme in the resistance measurement mode is presented in Fig. 6. In resistance measurement mode, the dependence expressed by formula (2) is used.

The scheme shows that the same current from the voltage source + U proceeds through the support resistor and the measured resistor R "(inputs of the inputs 35, 36, 30 and 31 are negligible) and the ratio U and U is equal to the resistance ratio of resistors R" and R ^. R1..R6 is used as reference resistors, R10 and R103 are used as current-folding. The ADC protection is provided by the R18 thermistor (in some cheap models, conventional resistors are used with a rating of 1.2 com), the Q1 transistor in stabitron mode (not always) and resistors R35, R16 and R17 at the inputs 36, 35 and 31 ADCs.

Serve Circuit Mode The call circuit is used IC2 chip (LM358) containing two operating amplifiers. On one amplifier, the sound generator is assembled, on the other - a comparator. At the voltage at the input of the comparator (output 6), less threshold, at its output (output 7), a low voltage opens the key on the transistor Q101, resulting in a beep. The threshold is determined by the R103, R104 divider. Protection is provided by the R106 resistor at the input of the comparator.

Defects Multimeters

All faults can be divided into factory marriage (and it happens) and damage caused by erroneous actions of the operator.

Since multimetting is used in multimeters, it is possible to closes the elements, bad solders and breakdowns of elements, especially located along the edges of the board. Repair of a faulty instrument should be started with a visual inspection of the printed circuit board. The most common factory defects M832 multimeters are shown in the table.

The serviceability of the LCD can be checked using an alternating voltage source with a frequency of 50.60 Hz and amplitude in a slight volt. As such a source of alternating voltage, you can take the M832 multimeter, which has a meander generation mode. To check the display, it is necessary to put it on a flat surface with the display upward, connect one M832 multimeter shorter to the overall display of the indicator (bottom row, left output), and the other multimeter probe is applied alternately to the rest of the display conclusions. If you manage to get the ignition of all the display segments, it means that it is working.

The faults described above may also appear during operation. It should be noted that in the mode of measuring constant voltage, the device rarely fails, because Well protected from overloads at the entrance. The main problems occur when measuring current or resistance.

Repair of a faulty instrument should be started from checking the supply voltage and health capacity of the ADC: stabilization voltage 3 V and lack of breakdown between power supply and total ADC output.

In the current measurement mode when using the inputs V, Q and MA, despite the presence of a fuse, there are cases when the fuse burns later than the safety diodes D2 or D3 have time to break through. If a fuse is installed in the multimeter, a fuse that does not correspond to the requirements of the instruction, then in this case the resistance of the R5 ... R8 is possible, and it can not be displayed visually on the resistances. In the first case, when only a diode makes itself, the defect manifests itself only in the current measurement mode: current through the device flows, but the display shows zeros. In case of burnout R5 or R6 resistors in voltage measurement mode, the instrument will oversee readings or show overload. With the full combustion of one or both resistors, the device is not reset in the voltage measurement mode, but when the inputs are closed, the display is set to zero. When combustion of R7 or R8 resistors on a current measurement ranges of 20 mA and 200 mA, the device will show overload, and in the range of 10 A - only zeros.

In the measurement mode of damage resistance occurs, as a rule, in the ranges of 200 Ohm and 2000 Ohm. In this case, when the voltage is applied to the input, resistors R5, R6, R10, R18 can be burned, the transistor Q1 and the C6 condenser is made. If the transistor Q1 is completely broken, then when measuring the resistance, the device will show zeros. In case of incomplete test of the transistor, the multimeter with open arrows will show the resistance of this transistor. In voltage measurement and current modes, the transistor closes the switch switch and the multimeter readings do not affect. When the C6 condenser break, the multimeter will not measure the voltage in the ranges of 20 V, 200 V and 1000 V or significantly underestimate the testimony in these ranges.

In the absence of an indication on the display in the presence of nutrition on the ADC or visually noticeable burnout of a large number of circuit elements, there is a high probability of damage to the ADC. The health of the ADC is checked by the voltage control of the source of the stabilized voltage of 3 V. In practice, the ADC flashes only when the high voltage is submitted to the input, much higher than 220 V. The cracks appear in the compound, the current of the microcircuit consumption increases, which leads to its noticeable heating. .

When a very high voltage is applied to the input of a very high voltage in the voltage measurement mode, a breakdown may occur by elements (resistors) and by printed circuit board, in the case of the voltage measurement mode, the diagram is protected by a divider on R1.R6 resistances.

In cheap models of the DT series, the long conclusions of parts can be condensed to the screen located on the back cover of the device, disrupting the operation of the scheme. Mastech has such defects are not observed.

The source of the stabilized voltage 3 V in the ADC in cheap Chinese models may in practice give a voltage of 2.6.3.4 V, and some devices cease to operate already at the voltage of the supply battery 8.5 V.

In DT models, low-quality ADCs are used, they are very sensitive to the rates of the C4 and R14 integrator chain. In Mastech multimeters, high-quality ADCs allow the use of elements of close nominal denominations.

Often in the DT multimeters when the applicants are open in the resistance measurement mode, the device is very long enough to the overload value ("1" on the display) or not set at all. "To cure" a poor-quality chip of the ADC can be reduced by R14 resistance rates with 300 to 100 com.

When measuring the resistance at the top of the range, the device "fills" the testimony, for example, when measuring the resistor resistance, 19.8 com shows 19.3 com. "It is treated" by replacing C4 capacitor to a capacitor of 0.22 ... 0.27 microf.

Since cheap Chinese firms use low-quality inapproprous ADCs, then there are no discontinuity break cases, and it can be very difficult to determine the cause of the fault, and it can differ in different ways, depending on the torn output. For example, one of the indicator conclusions does not burn. Since multimeters use displays with a static display, to determine the cause of the fault, it is necessary to check the voltage at the corresponding output of the ADC chip, it should be about 0.5 V relative to the overall output. If it is zero, then the ADC is defective.

An effective way to find the cause of the malfunction is the transversion of the analog-digital converter chip converter as follows. It is used one more, of course, a good, digital multimeter. It is included in the mode of checking diodes. Black probe, as usual, is installed in the COM socket, and the red into the VQMA jack. The red appliance probe is connected to the conclusion 26 (minus power), and black alternately concerns each leg of the ADC chip. Since protective diodes are installed on the inputs of an analog-digital converter in reverse turning on, then with such a connection, they should open, which will be reflected on the display as a voltage drop on the open diode. The real value of this voltage on the display will be somewhat larger, because The scheme includes resistors. Similarly, all the conclusions of the ADC are checked when the black probe is connected to the conclusion 1 (the plus of the ADC nutrition) and the alternately touch of the remaining conclusions of the microcircuit. The instrument readings must be similar. But if you change the polarity of inclusion with these checks on the opposite, the device should always show a break, because The input resistance of a good chip is very large. Thus, the conclusions can be considered defective, which show the final resistance at any polarity of the connection to the chip. If the device shows a cluster for any connection of the output under study, this is ninety percent talking about the inner break. The specified method of checking is quite universal and can be used when checking various digital and analog microcircuits.

There are malfunctions associated with poor-quality contacts on a gallery switch, the device only works when the gallets is pressed. Firms that produce cheap multimeters rarely cover the tracks under the lubricant's gallery switch, which they are quickly oxidized. Often the tracks are somewhat polluted. Repaired as follows: The printed circuit board is removed from the housing, and the switch paths are cleaned with alcohol. Then the thin layer of technical vaseline is applied. All, the device is fixed.

The instruments of the DT series sometimes happens that the alternating voltage is measured with a minus sign. This indicates incorrect installation D1, usually due to improper marking on the diode housing.

It happens that manufacturers of cheap multi-dimet-ditchs put low-quality operational amplifiers in the chain of the sound generator, and then when the device is turned on, the buzzment of the buzzer is distributed. This defect is eliminated by the electrolytic capacitor with a rating of 5 μF in parallel to the power chain. If this does not provide a steady operation of the sound generator, it is necessary to replace the operational amplifier on LM358P.

Often there is such a nuisance as battery leakage. Small drops of electrolyte can be wiped with alcohol, but if the fee flooded strongly, then good results can be obtained by flushing it with hot water with a household soap. After removing the indicator and disappearing a squeeze, using a brush, such as tooth, you need to thoroughly clean the board on both sides and rinse under the jet of water from the tap. Repeating the sink 2.3 times, the fee is dried and installed in the housing.

In most devices produced recently, adversary (DIE CHIPS) ADCs are applied. The crystal is installed directly on the printed circuit board and is poured by a resin. Unfortunately, this significantly reduces the maintainability of the instruments, because When leaving the ADC, it is often found quite often, it is difficult to replace it. Instruments with inapproprous ADC are sometimes sensitive to bright light. For example, when working next to the desktop lamp, measurement errors may increase. The fact is that the instrument indicator and fee have some transparency, and the light, penetrating them, falls on the CRP crystal, causing a photo effect. To eliminate this disadvantage, you need to remove the board and, removing the indicator, take the location of the ADC crystal (it is clearly visible through the fee) with tight paper.

When you buy multimeters DT, you should pay attention to the quality of the switch mechanics, it is necessary to scroll the Multimeter's gallery switch several times to make sure that the switch is clearly and without hots: plastic defects are not repaired.

Read more ...

In different places you have to catch fish. It also happens where the heat center or other economic services is discharged water used to cool the aggregates of thermal power plants, and several additional degrees sometimes lead to an increased concentration of fish of some rocks in such places.

It is well known that at temperatures above 25 ° C in low-propelled and shallow waters, the degree of saturation with oxygen is almost equal to zero, and this creates conditions in which it is difficult to survive the fish of certain breeds.

This microcircuit has gained widespread in the measuring technique. Almost all multimeters (release of the 90s and 2000s) were used as a "brain". To restore almost lost devices and ordered. I will repair everything well known (or almost everyone) Mastech M890F device. Overview exclusively for those friendly with a soldering iron.
I ordered these microcircuits in the middle of August. They walked a little more than a month.


Unfortunately, this product is currently unavailable. Bought spontaneously. The decisive role was played by the price. At one time, our company ordered these MS in a well-known Moscow firm. The price has changed a bit in accordance with the dollar.


The price of about 33 rubles per piece on Ali is almost a gift. But this is not the essence. I'll tell you why I took, and what I did.
And first we look at how they packed and in what form everything came out. This information is sometimes important.


Standard paper package, "Propupus" from the inside.


Microcircuits with their legs were inserted into foamed polyethylene (he tried to explain how he could), so none suffered.


These chips are in one of the most popular Mastech M890F multimeters. But not only in them. They are used in other devices of this company (and not only). The most common: M830, M832, M838.
The basis of this device (M890F), as well as most inexpensive multimeters, is an analog-digital ICL706 converter operating on the principle of double integration. This is a complete analogue of the well-known domestic IC K572PV5. You can use it as a repair kit. But it is more expensive.
The main errors of operation, resulting in a malfunction of the instrument, are measuring with overload overload and selection of incorrect measurement mode as a result of inattention or rush. This leads to a breakdown of the ADC, burden of tracks, failure of other microcircuits. No less dangerous is to switch limits and measurement modes without disconnecting from the measured circuit. At the same time, the conductive switches tracks are often fused. As a result, the device is no longer repaired. This is a disadvantage of all devices from a similar type by switches.
What exactly was the cause of damage to this multimeter, I do not know.


The tracks were evaporated at: 20k, 200kom and 200mv. Theoretically, and they can be restored. But this is the art of appliqués. In the meantime, I will test my strength in the art of repair :)
I have them (multimeters) several pieces have fallen. He himself personally did not burn anyone. Faulty collected from acquaintances. Ten years ago, repairs were inexpedient because of the cost of the microcircuit (already wrote). Yes, and restore such devices can only be taken into account by their future disability. Part of the functions will be lost irretrievably, even after recovery. Tracks back not to glue. :(
Here he is the most common multimeter.

Vidosh he has of course worn. But it's a lot of years.
With frequent disclaims, one or more cable wiring is broken, well, very hard.


Options are only two: either not climb or overpass.

As you can see, I spare. The procedure is tedious.


In this device, in addition to the processor, printing conductors are controversial. I restored them. There are several exemplary resistances. They must be selected very accurately. The error of the entire instrument depends on them. These resistances in the marking on one strip larger.
There are also such copies.


This is a slightly different device, although the same company. But as an example is suitable. It is clearly seen that the board burned in the measurement mode of resistance. This is where to stick so that such a hole formed in the board!
I understood that. But not everyone knows that the voltage in the network is measured in volts, and not in Omah :)
It is also possible to restore, but some measurement limits will have to donate. But this will be another story ...
And this is M832, which is no longer restored.


In such multimeters, you must first remove the "klyaksu", then solder the chip to the printed contacts. They kindly provided.
Return to M890.
The first thing for progars of the board and burnout printed conductors turn out to be faulty IC1 processor, IC8 7555 integral timer and two MS LM358 container tank. Faulty MS often plant supply voltage. IC8 7555 is located on top board.
Current consumption of a good multimeter about 4mA. Specifically, the processor consumes a little less than 2nd. And nothing else. It must be remembered. Increased consumption current talks about any malfunction.
I attach an edited multimeter scheme. It is very convenient to repair and calibrate the device. The scheme was originally downloaded from the Internet and edited for several years. In the scheme there may be shortcomings. Perhaps and did not all manage to correct.

IC8 7555 You can simply drop out of the scheme that I did. Multimeter will not be able to measure the frequency. For me it is not critical.
On the Internet there is also a scheme with a later modification of this device.

This (so to speak) is a completely different device. In my opinion, more poor. The scheme has simplified.
All elements of the scheme are assembled on the same board. Purely externally (without autopsy) is very difficult to distinguish, unless it is easier for weight. And sold for a few years later and cheaper.
I proceed directly to repair.
To determine what happened, it is necessary to learn the top fee. To do this, unscrew four small screws and remember how the lamellas are located at the switch. They have a peculiar feature at the most inopportune moment. And it is best to immediately remove, so as not to look for them later on the floor.

The device works well and without top board. It is only necessary to move 2 and 6 connector contacts (I marked them in the figure). On them passes 9V. It will disappear and the measured values \u200b\u200bon the display will disappear. When repaired, this is not very important.
Almost always burns the protective transistor Q4 (9014).

I already dropped it. Multimeter can work without it. But it is better to replace. What a, but still protection.
Now you need to measure the voltage between the legs 1 and 32 of the processor. In this case, the rotator of the repaired multimeter should stand in any mode, except for measuring resistance.


It must be approximately within the specified limits (2.8-3.0V). When exceeding the values \u200b\u200b(usually more than 6B) with a probability of a 99% of the Device processor.
Percents itself is on the other side of the board under the indicator. To get to it, you need to unscrew four screws and remove the module with the indicator.
These chips are in Mastech M890F multimeters. More often met "blots".


And in that and in another case, a faulty chip is falling. Instead, it is placed by the usual MS from China. What I successfully did.


You can get our analog of kr572fv5. At the time it was soldered into another faulty device. For years already works.

That's just the distance between the legs is slightly different. There will be a little bit.
After the procedures have done, the multimeter came to life. Measured the voltage on the battery.


Almost true. It remains to configure the multimeter for exemplary instruments. But not all they have. Alternatively, you can adjust the testimony by comparing with another device to which you have trust.
Begin it is necessary from calibration of constant stresses (VR1). And only then variables (VR2). The sequence of other adjustments to the "speed" does not affect :)
The accuracy of measurement of resistance is determined by the accuracy of the sample resistance inside the instrument and no potentiometers are regulated.
That's all.
And something else at the end.
I tried to tell about the use of ICL706 chip as Remkomplekt. It is impossible to describe all malfunctions in multimeters in which their replacement is necessary. To whom something is unclear about the chips, ask questions. For the repair tips, please contact PM.
I hope at least someone helped.
Good luck everyone!