Repair analysis method for multimeter
1, Repair essentials
Exploring obstacles 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 essentials can generally be divided into the following types:
1. It is believed that relying on the senses can directly make decisive decisions on the causes of obstacles. Through surface inspection, inventions such as broken wires, desoldering, short circuits, broken fuse tubes, burnt components, mechanical damage, copper foil lifting and breaking on printed circuits can be invented; You can touch the temperature rise environment of the battery, resistor, transistor, and integrated block, and refer to the circuit diagram to find the reason for the very high 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 voltage at each key point is normal, which can quickly identify obstacles. Measure the operating voltage and reference voltage of the A/D converter.
3. Short circuit method is commonly accepted in the inspection of A/D converters mentioned earlier, and this method is more commonly used in repairing weak and micro electrical instruments.
4. The circuit breaker method stops the suspicious department from being disconnected from the entire machine or unit circuit. If the obstruction dissipates, it manifests as obstruction in the disconnected circuit. This method is important in environments where there is a short circuit in the circuit.
5. When the obstruction has been reduced to a certain location or several components, online or offline measurement can be carried out. When necessary, replace with good components. If it hinders dissipation, it indicates that the components are damaged.
6. The disturbance method uses the voltage felt by the human body as a disturbance signal to observe the changing environment of LCD performance. It is commonly used to check whether the input circuit and the display department are complete.
