Multimeter Fault Analysis and Repair Methods
Fault troubleshooting shall follow the principle: from outside to inside, from simple to complex, break down the whole into parts, and focus on key points. The main methods are listed below:
① Sensory Inspection Method Judge the fault cause directly by human senses. Visual inspection can detect broken wires, cold solder joints, short circuits caused by overlapping wires, blown fuses, burned components, mechanical damage, lifted or fractured copper traces on printed circuits, etc. Touch to check the temperature rise of batteries, resistors, transistors and integrated circuits, and find the cause of abnormal temperature rise with reference to the circuit diagram. In addition, manually check loose components, poorly inserted IC pins and stuck
selector switches. Listen and smell for abnormal noise or odors.
② Voltage Measurement Method Measure the operating voltage at each key point to quickly locate faults, such as measuring the operating voltage and reference voltage of the A/D converter.
③ Short-circuit Method As introduced previously in A/D converter inspection, the short-circuit method is commonly adopted. It is widely used for repairing weak-current and microelectronic instruments.
④ Open-circuit Method Disconnect the suspected section from the whole device or individual circuit. If the fault disappears, the fault lies within
the disconnected circuit. This method is especially suitable for circuits with short-circuit faults.
⑤ Component Measurement Method When the fault is narrowed down to a certain position or several components, perform in-circuit or off-circuit measurement on them. If necessary, replace with a good component. If the fault disappears, the tested component is defective.
⑥ Interference Injection Method Use human-body induced voltage as an interference signal and observe changes on the liquid crystal display. This method is commonly used to verify whether the input circuit and display unit work normally.
