Common Fault Diagnosis and Troubleshooting for Digital Multimeters
Ⅰ. Visual Inspection
Manually check whether the battery, resistors, transistors and integrated circuits have excessive temperature rise. If a newly‑installed battery gets hot, it may indicate a circuit short‑circuit. In addition, inspect the circuit for broken wires, desoldering, mechanical damage and other defects.
Ⅱ. Measurement of Operating Voltages at All Stages
Measure the operating voltage at each point and compare it with the normal value. First of all, ensure the accuracy of the reference voltage. It is preferable to use a digital multimeter of the same or similar model for measurement and comparison.
Ⅲ. Waveform Analysis
Use an electronic oscilloscope to observe the voltage waveform, amplitude, period (frequency), etc. at key points of the circuit.
For example, check whether the clock oscillator starts oscillation and whether its oscillation frequency is 40 kHz. If there is no output from the oscillator, the internal inverter of TSC7106 may be damaged, or external components may have an open circuit.
The waveform at pin 21 of TSC7106 should be a 50 Hz square wave. Otherwise, the internal 200‑divider may be damaged.
Ⅳ. Measurement of Component Parameters
Perform in‑circuit or off‑circuit measurement and parameter analysis for components within the faulty range. When measuring resistors in‑circuit, take into account the influence of components connected in parallel.
Ⅴ. Troubleshooting of Intermittent Hidden Faults
Hidden faults refer to intermittent failures where the instrument works erratically. Such faults are relatively complex. Common causes include cold‑soldered or loose solder joints, loose connectors, poor contact of the rotary switch, unstable component performance, and partially broken leads.
In addition, such faults can also be caused by external factors, such as excessive ambient temperature, high humidity, or nearby intermittent strong interference signals.
