① Replacement method
Use a good component to replace the suspect component, or put the suspect component on a good power distribution box or machine to work in the field, to confirm its good or bad, can also take the suspect component down to the test bench to test. This substitution is very convenient for components that can be swapped out, but it requires a large number of spare parts and an equally good machine.
(2) Comparative method
In advance, all the signals of the initial power-on state of a good machine are tested according to the input and output states of the components, and drawn into a table or waveform atlas. When the machine fails, it can be measured point by point and compared and analyzed to find out the faulty components. When testing, you can use a multimeter or oscilloscope.
③ Test component internal resistance method
The input pin or output pin of a general component has a certain resistance to the ground or to the power end. Use a common multimeter to measure the positive and negative resistance (the specific resistance value varies with the component). Generally, the forward resistance is between tens of ohms and 100 ohms, while the reverse resistance is between hundreds of Ohms and 1000 ohms. In general, the forward resistance value will not equal or approximate zero, and the reverse resistance value will not equal infinity (sometimes with the exception of some linear components or thick film circuits). If the resistance value cannot be determined, you can compare other components of the same model in the same PDB.