Multimeter repair and analysis methods
Repair essentials
When looking for obstacles, you should first look at the outside and then the inside, first the easy and then the difficult, break them into parts, and focus on breakthroughs. The essentials can be roughly divided into the following categories:
1. Sensors cannot directly determine the cause of the failure by relying on the senses. Through superficial inspection, it can be found such as broken wires, desoldering, short circuits, broken fuse tubes, burned components, mechanical damage, and copper foil on printed circuits. Warping and breakage, etc.; you can touch the temperature rise of batteries, resistors, transistors, and integrated blocks. You can refer to the circuit diagram to find out the cause of the abnormal temperature rise. In addition, you can also use your hands to check whether the components are loose, whether the integrated circuit pins are firmly inserted, and whether the transfer switch is stuck; you can hear and smell whether there are any strange sounds and smells.
2. Voltage measurement method: Measuring whether the working voltage of each key point is normal can quickly find the fault point. Such as measuring the working voltage and reference voltage of the A/D converter.
3. Short-circuit method: The short-circuit method is generally used in the above-mentioned inspection methods of A/D converters. This method is often used when repairing weak current and micro-electrical instruments.
4. Circuit breaking method: Isolate the suspicious part from the whole machine or unit circuit. If the fault disappears, it means 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. Component measurement method: When the fault has been reduced to a certain component or several components, it can be measured online or offline. If necessary, replace it with good components. If the fault disappears, it means that the component is bad.
6. Interference method: Use the voltage induced by the human body as an interference signal to observe the changes in the LCD display. It is often used to check whether the input circuit and the display part are complete.
