1. Appearance inspection method

Observe whether there is any burnt place on the circuit board, whether there is any fracture in the copper coating, whether there is any odor on the circuit board, whether there is any place with poor welding, and whether there is any mildew and blackness on the interface and gold finger.

2. Principle analysis method

This method is to analyze the working principle of a circuit board. For engineers, some boards, such as switching power supply, can know the working principle and details without circuit board drawings. For engineers, things that know the schematic diagram of a PCB are extremely simple to maintain.

3. Comparison method

The comparison method is one of the most commonly used methods for maintenance of circuit boards without drawings, which has been proved to be very effective in practice. The purpose of finding faults is achieved by comparing the status of good boards with that of good boards. Abnormalities are found by comparing the curves of each node of two PCB boards.

4. Grounding circuit method

The circuit building method refers to the method of making a circuit by hand, which can work after installing the missing integrated circuit, so as to verify the quality of the tested integrated circuit. The accuracy of this method can reach 100%, but it is difficult to build a set of circuits for all ICs with various types and complex packaging.

5. State method

The state method is to check the normal working state of each component. If the working state of a component does not conform to the normal state, there is a problem with the component or its affected components. The state method is the most accurate one among all maintenance methods, and its operation difficulty is beyond the grasp of ordinary engineers, which requires rich theoretical knowledge and practical experience.

6. Pass kill method

All components shall be tested until the defective components are found, so as to achieve the purpose of repair. If the components cannot be detected by the instrument are encountered, new components shall be used to replace them, so as to finally ensure that all electronic components on the board are good, so as to achieve the purpose of repair. This method is simple and effective, but it is powerless to solve the problems such as through hole impassability, copper coating fracture, improper potentiometer adjustment, etc.