Operating Methods and Repair Tips for Digital Multimeters
① Sensory Inspection Method Judge the cause of faults directly by human senses. Visual inspection can detect broken wires, cold solder joints, bridging short circuits, blown fuses, burned components, mechanical damage, lifted or fractured copper traces on printed circuits, etc. Touch components such as batteries, resistors, transistors and integrated circuits to check for excessive temperature rise, and refer to the circuit diagram to locate the cause of abnormal heating. In addition, manually check for loose components, securely inserted IC pins and stuck rotary switches. Listen for abnormal sounds and smell for unusual odors.
② Voltage Measurement Method Quickly locate fault points by measuring whether the operating voltage at each key test point is normal, such as the operating voltage and reference voltage of the A/D converter.
③ Short-Circuit Method The short-circuit method is commonly adopted in the aforementioned inspection procedures for A/D converters and widely used when repairing weak-current and microelectronic instruments.
④ Open-Circuit Method Disconnect the suspected section from the complete device or unit circuit. If the fault disappears, the defect lies within the disconnected circuit. This method is mainly applicable to circuits with short-circuit faults.
⑤ Component Measurement Method Once the fault is narrowed down to a certain area or several components, perform in-circuit or off-circuit measurements. If necessary, replace the suspect part with a known-good component. If the fault disappears after replacement, the original component is defective.
⑥ Interference Method Use human induced voltage as an interference signal and observe changes on the LCD display. This method is often used to verify whether the input circuit and display section work properly.
