Repair methods and techniques for digital multimeters
Digital instruments have high sensitivity and accuracy, and their applications are almost ubiquitous in all enterprises. However, due to its multifactorial nature and high randomness in encountering problems, there are not many rules to follow, making repair difficult. Therefore, I have compiled some of the repair experience accumulated in years of practical work for reference by colleagues in this field. The capacitive voltage divider high-voltage measurement system is suitable for measuring pulse high voltage, lightning high voltage, and power frequency high voltage, and is an alternative to high-voltage static voltage meters.
1, Repair method:
Finding faults should start from the outside and then from the inside, from easy to difficult, break them down into smaller parts, and focus on breakthroughs. The methods can be roughly divided into the following:
The sensory method directly judges the cause of the malfunction based on the senses. Through visual inspection, it can detect issues such as broken wires, desoldering, short circuits, broken fuse tubes, burnt components, mechanical damage, copper foil lifting and breaking on printed circuits, etc; You can touch the temperature rise of the battery, resistor, transistor, and integrated block, and refer to the circuit diagram to identify the cause of abnormal temperature rise. In addition, you can also check by hand whether the components are loose, whether the integrated circuit pins are securely inserted, and whether the conversion switch is stuck; You can hear and smell any unusual sounds or odors.
2. The voltage measurement method measures whether the working voltage of each key point is normal, which can quickly identify the fault
Obstacles. Measure the working voltage and reference voltage of the A/D converter.
3. Short circuit method is generally used in the inspection of A/D converters mentioned earlier, which is more commonly used in repairing weak and micro electrical instruments.
4. The circuit breaker method interrupts the suspicious part from the entire machine or unit circuit. If the fault disappears, it indicates that the fault is in the disconnected circuit. This method is mainly suitable for situations where there is a short circuit in the circuit.
5. When the fault has narrowed down to a certain location or several components, online or offline measurement can be performed. If necessary, replace with good components. If the fault disappears, it indicates that the component is damaged.
6. Interference method uses human induced voltage as interference signal to observe the changes in LCD display, commonly used to check whether the input circuit and display part are intact.
