General troubleshooting method for digital multimeter failure - Database & Sql Blog Articles

Crystal oscillator

Quartz Oscillator 3225 20M OSC

Digital multimeter troubleshooting should generally start with the power supply. For example, after the power is turned on, if the liquid crystal cell is displayed, first check if the voltage of the 9V laminated battery is too low; if the battery lead is disconnected. To find faults, you should follow the order of “before and after, first and then difficult”. Troubleshooting the DMM can be done as follows.

First, the appearance check

You can touch the temperature of the battery, resistor, transistor, and integrated block by hand. If the newly installed battery is hot, the circuit may be shorted. In addition, you should also observe whether the circuit is broken, desoldered, mechanically damaged, etc.

Second, test the working voltage at all levels

Detect the working voltage of each point and compare it with the normal value. Firstly, ensure the accuracy of the reference voltage. It is best to use a digital multimeter of the same model or similar to measure and compare.

Third, the waveform analysis

Observe the voltage waveform, amplitude, period (frequency) of each key point of the circuit with an electronic oscilloscope. For example, if the clock oscillator is oscillated, the oscillation frequency is 40 kHz. If the oscillator has no output, the internal inverter of the TSC7106 is damaged, or the external component may be open. Observe that the waveform of the {21} pin of TSC7106 should be a 50Hz square wave. Otherwise, it may be the damage of the internal 200 divider.

Fourth, measuring component parameters

For online or offline measurements of components within the fault range, the parameter values ​​should be analyzed. For on-line measurement of resistance, the effects of components connected in parallel should be considered.

Five, hidden troubleshooting

The hidden fault refers to the fault that occurs when the fault occurs, and the fault of the instrument is good or bad. Such faults are more complicated. Common causes include solder joints, loose soldering, loose connectors, poor contact of the transfer switch, 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 is intermittent strong interference signal nearby.