Principle 1: Look first, measure later

　　The circuit board to be repaired should first be visually inspected. If necessary, a magnifying glass should also be used for observation.

　　Mainly looking at:

　　1. Are there any broken wires or short circuits; Especially whether there is any breakage or adhesion in the connecting wires of the printed circuit board;

　　2. Whether there is disconnection phenomenon in relevant components such as resistors, capacitors, inductors, diodes, and transistors;

　　Has anyone repaired it? What components have been touched? Is there any problem of virtual welding, missing welding, reverse insertion, or incorrect insertion.

　　After ruling out the above conditions, first use a multimeter to measure the resistance value between the power supply and ground of the circuit board. Generally, the resistance value of the circuit board should not be less than 70 Ω. If the resistance value is too small, it is only a few or ten ohms. This indicates that there are components on the circuit board that have been broken down or partially broken down, and measures must be taken to identify the broken components. The specific method is to power up the repaired board (note! At this time, it is necessary to make sure that the voltage value and polarity of the working voltage of the board are not connected incorrectly and add a voltage value higher than the working voltage. Otherwise, it will cause damage to the circuit board to be repaired. If the old fault is not ruled out, new problems will be added). Use a point thermometer to measure the temperature of each component on the circuit board, and the temperature will rise quickly and higher. Be a key suspect.