Five Methods for Troubleshooting Digital Multimeter Faults
Troubleshooting digital multimeters should generally start with the power supply. For example, if the LCD shows nothing after turning on the power, first check whether the 9V battery voltage is too low or whether the battery leads are broken. Fault location should follow the principle: "inside first, outside later; easy first, difficult later". The following methods are commonly used for troubleshooting digital multimeters.
Five Common Methods for Troubleshooting Digital Multimeters
1. Visual and Physical Inspection
Check by touch whether the battery, resistors, transistors, or integrated circuits become excessively hot. If a newly installed battery heats up, it usually indicates a short circuit in the circuit. In addition, inspect the circuit for broken wires, cold solder joints, mechanical damage, and other defects.
2. Operating Voltage Measurement
Measure the operating voltage at various points and compare the readings with normal values. First, ensure the accuracy of the reference voltage. It is best to use a digital multimeter of the same or similar model for measurement and comparison.
3. Waveform Analysis
Use an oscilloscope to observe the voltage waveform, amplitude, period (frequency), and other parameters at key circuit points. For example, check whether the clock oscillator is running and whether its frequency is 40 kHz. If the oscillator has no output, the internal inverter of TSC7106 may be damaged, or an external component may be open-circuited. The waveform at pin 21 of TSC7106 should be a 50 Hz square wave; otherwise, the internal divide‑by‑200 counter may be faulty.
4. Component Parameter Measurement
Perform in-circuit or off-circuit measurement on components within the suspected faulty area and analyze the measured parameters. When measuring resistors in-circuit, consider the influence of parallel components.
5. Intermittent Fault Troubleshooting
Intermittent faults are faults that appear and disappear irregularly, causing the meter to work intermittently. Such faults are relatively complex. Common causes include cold solder joints, loose connections or connectors, poor contact of selector switches, unstable component performance, and partially broken leads. External factors may also be responsible, such as excessively high ambient temperature, high humidity, or nearby intermittent strong interference signals.
