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, if the LCD has no display after turning on the power, you should first check whether the voltage of the 9V laminated battery is too low and whether the battery lead is disconnected. When looking for faults, you should follow the order of "first inside then outside, first easy then difficult". Digital multimeter troubleshooting can generally be carried out as follows:

(1) Appearance inspection:
You can touch the battery, resistor, transistor, and integrated block with your hands to see if the temperature is too high. If the newly installed battery is hot, it means the circuit may be short-circuited. In addition, you should also observe whether the circuit is disconnected, desoldered, mechanically damaged, etc.

(2) Detect the working voltage at all levels:

(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 oscillating and whether the oscillation frequency is 40 kHz. 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 50 Hz square wave. Otherwise, the internal 200 frequency divider may be damaged.

(4) Measuring element parameters:

(5) Hidden troubleshooting: