Introduction to five methods for troubleshooting digital multimeters
A digital multimeter is a measuring instrument that uses the analog/digital conversion principle to convert the measured quantity into a digital quantity and displays the measurement results in digital form. Compared with pointer multimeters, digital multimeters have the advantages of high precision, fast speed, large input impedance, digital display, accurate readings, strong anti-interference ability, and high degree of measurement automation and are widely used. However, if used improperly, it may cause malfunction.
Digital multimeter troubleshooting should generally start with the power supply. For example, after the power is turned on, if the liquid crystal element displays, you should first check whether the voltage of the 9V laminated battery is too low; whether the battery lead is disconnected. Finding faults should follow the order of "first inside then outside, first easy then difficult". Digital multimeter troubleshooting can generally be carried out as follows.
Five general methods for troubleshooting digital multimeters
1. Appearance inspection: You can touch the battery, resistor, transistor, and integrated block with your hands to see if the temperature rise is too high. If a newly installed battery becomes hot, the circuit may be short-circuited. In addition, the circuit should also be observed for disconnection, desoldering, mechanical damage, etc.
2. Detect the working voltage at all levels: Detect the working voltage at each point and compare it with the normal value. First, ensure the accuracy of the reference voltage. It is best to use a digital multimeter of the same model or a similar one for measurement and comparison.
3. Waveform analysis: Use an electronic oscilloscope to observe the voltage waveform, amplitude, period (frequency), etc. of each key point in the circuit. For example, test whether the clock oscillator starts to oscillate and whether the oscillation frequency is 40kHz. If the oscillator has no output, it means that the internal inverter of TSC7106 is damaged, or the external component may be open circuit. Observe that the waveform at pin {21} of TSC7106 should be a 50Hz square wave. Otherwise, the internal 200 frequency divider may be damaged.
4. Measure component parameters: Perform online or offline measurements on components within the fault range, and analyze parameter values. When measuring resistance online, the influence of components connected in parallel with it should be considered.
5. Hidden fault elimination: Hidden fault refers to the fault that appears and disappears, and the instrument is good and bad sometimes. This type of failure is relatively complex. Common causes include weak solder joints, loose joints, loose connectors, poor contact of the transfer switch, unstable component performance, and continuous breakage of leads. In addition, it also includes some external factors. Such as the ambient temperature is too high, the humidity is too high or there are intermittent strong interference signals nearby, etc.
