1. Measuring voltage method to find faulty PCB board
The first thing to confirm is whether the voltage of each chip's power supply pin is normal, and then check whether the various reference voltages are normal, and whether the working voltage of each point is normal. For example, when a general silicon transistor is turned on, the BE junction voltage is about 0.7V, and the CE junction voltage is about 0.3V or less. If the BE junction voltage of a triode is greater than 0.7V (except for special triodes, such as Darlington), it may be that the BE junction is open.
2, signal injection method to find faulty PCB board
Add the signal source to the input, and then measure the waveform of each point backwards to see if it is normal to find the fault point. Sometimes we will use a simpler method, such as holding a dice by hand, touching the input terminals of each level to see if there is any reaction at the output, which is often used in audio, video and other amplifier circuits (but note that the hot backplane This circuit cannot be used for circuits or circuits with high voltages, otherwise it may cause electric shock. If there is no reaction at the previous level and there is a reaction at the next level, the problem is at the previous level and should be checked.
3. Other methods for finding faulty PCB boards
There are many other ways to find fault points, such as watching, listening, smelling, and touching.
“Look” is to see if the component has obvious mechanical damage, such as cracking, blackening, deformation, etc.
"Listening" means listening to whether the working voice is normal. For example, some things that should not be ringing are ringing, the place where the ringing is not ringing or the sound is not normal, etc.;
"Smell" is to check for odor, such as the smell of burnt, the taste of the capacitor electrolyte, etc., which is very sensitive to an odor for an experienced electronic maintenance person;
"Touching" is to test the temperature of the device by hand, such as too hot, or too cold.
Some power devices generate heat when they work. If they are cold, they can basically be judged that they are not working. But if the hot place is not hot or the hot place is too hot, it will not work. General power triodes, voltage regulator chips, etc., working below 70 degrees is completely ok. What is the concept of 70 degrees? If you put your hand on it, you can stick it for more than three seconds, which means the temperature is about 70 degrees (be careful to test it first, don't burn your hand).