A digital multimeter (DMM) is a measuring instrument that uses the principle of analog-to-digital conversion to convert the measurement into a digital quantity and display the measurement results in digital form. Compared with the pointer type multimeter, the digital multimeter has the advantages of high precision, fast speed, large input impedance, digital display, accurate reading, strong anti-interference ability, and high degree of measurement automation. It is widely used. But if used improperly, it is easy to cause malfunction.

This article takes the digital multimeter DT-830 as an example to talk about the general troubleshooting method of the digital multimeter.

Digital multimeter troubleshooting should generally start with the power supply. For example, after the power is turned on, if the LCD cell displays, you should first check whether the voltage of the 9V stacked battery is too low; whether the battery lead is disconnected. Finding faults should follow the order of "first in and then out, first and then hard". The troubleshooting of digital multimeter can be roughly carried out as follows.

1. Visual inspection.

You can touch whether the temperature rise of the battery, resistor, transistor and integrated block is too high. If the newly installed battery heats up, the circuit may be short-circuited. In addition, you should also observe whether the circuit is broken, unsoldered, mechanically damaged, etc.

Second, detect the working voltage at all levels.

Check the working voltage of each point and compare it with the normal value. First of all, the accuracy of the reference voltage should be ensured. It is best to use a digital multimeter of the same model or similar for measurement and comparison.

3. Waveform analysis.

Use an electronic oscilloscope to observe the voltage waveform, amplitude, period (frequency) of each key point of the circuit. For example, if it is tested whether the clock oscillator is oscillating, whether the oscillation frequency is 40 kHz. If there is no output from the oscillator, it means that the internal inverter of the TSC7106 is damaged, or the external components may be open. Observe that the waveform at the {21} pin of TSC7106 should be a 50Hz square wave, otherwise, the internal 200 frequency divider may be damaged.

4. Measure the component parameters.

For the components within the fault range, online or offline measurement should be performed to analyze the parameter values. For online resistance measurement, the influence of components connected in parallel should be considered.

5. Resolve hidden faults.

Hidden failure refers to the failure that is hidden when the failure occurs, and the instrument is good or bad. Such failures are more complicated. Common causes include virtual solder joints, loosening, loose connectors, poor contact of transfer switches, unstable component performance, and continuous lead wire breakage. In addition, it also includes some external factors. If the ambient temperature is too high, the humidity is too high, or there are intermittent strong interference signals nearby, etc.

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