The circuit board should be treated with visual inspection first. If necessary, it should also be observed with the help of a magnifying glass.
Mainly look at:
1. Whether there are disconnection and short circuit, especially on the circuit board of the printed circuit board cable is broken adhesion and other phenomena;
2. Related components such as resistive capacitance inductor diode transistor, such as whether there is disconnection phenomenon;
3. Have anyone repaired what components have been moved? There are some problems, such as the existence of virtual welding leakage welding plugging and plugging errors. When the above condition is excluded, the resistance between the circuit board power supply and the ground is measured with a multimeter. Usually the value of the circuit board should not be less than 70 Omega. If the resistance value is too small, only a few or more than 10 ohms. It is shown that if there are components on the circuit board that are penetrated or partially penetrated, measures must be taken to find the components that have been penetrated. The specific way is to add electricity to the repaired plate (note! At this time be sure to understand the voltage value of the plate's operating voltage and the positive and negative polarity can not be connected incorrectly and add higher than the operating voltage value. Otherwise will treat the repair circuit board has the damage! Old fault did not rule out and add new trouble!!)
Using the point temperature meter to measure the temperature of each device on the circuit board, the temperature rise of the faster and higher is regarded as the key skeptical object. If the resistance value is normal, then the multimeter is used to measure the resistance container on the plate two, the transistor field effect tube and the stripping switch and other components. The goal is to first make sure that the components that have been measured are normal. Don't complicate a problem that can be solved with a general test tool, such as a multipurpose table.