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Digital multimeter troubleshooting general method

The digital multimeter (DMM) is a measuring appearance that uses the principle of analog-to-digital conversion to convert the measured quantity into a digital quantity and digitally display the measured result. Compared with the pointer multimeter, the digital multimeter is widely used because of its high precision, high speed, high input impedance, digital display, accurate reading, strong anti-interference ability and advanced measurement automation. However, if used improperly, it is easy to form a problem.
    Digital multimeter troubleshooting should usually start with a power source. Finding faults should follow the order of “before and after, first and then difficult”. Digital multimeter troubleshooting can be carried out as follows.
First, the appearance of viewing.
    The temperature rise of the battery, resistor, transistor, and integrated block that can be touched by hand is not too high. If the newly loaded battery is hot, clarify that the circuit may be shorted. In addition, it should also investigate whether the circuit is broken, de-soldered, mechanically damaged, etc.
Second, check the operating voltage at all levels.

    Check the operating voltage at each point and compare it with the normal value. Firstly, ensure the accuracy of the reference voltage. It is best to measure and compare with a digital multimeter of the same type or proximity.
Third, the waveform analysis.
    Use an electronic oscilloscope to investigate the voltage waveform, undulation, period (frequency), etc. of each critical point of the circuit.
Fourth, measure component parameters.
    For on-line measurement or offline measurement of components within the fault range, the parameter values ​​should be analyzed. When measuring the resistance on-line, consider the effects of the components in parallel with it.
Fifth, the hidden problem is removed.
    The recessive problem refers to the problem of being insidious when the disease occurs, and the appearance is good and bad. Such problems are complicated and complicated. Common elements include solder joints, loose soldering, loose connectors, poor contact of the transfer switch, unstable component functions, and continuous lead disconnection. In addition, it also contains some external factors. If the ambient temperature is too high, the humidity is too high or there is intermittent strong interference signal.

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