Generally, there are several ways to find faults:
The first thing to be confirmed is whether the voltage of each chip power supply pin is normal, and then check whether various reference voltage is normal, in addition, whether the operating voltage of each point is normal.For example, the BE junction voltage is about 0.7v while the CE junction voltage is about 0.3v or less when the silicon triode is conductive.If the BE junction voltage of a audion is greater than 0.7v (except for special audion, such as darlington tube, etc.), the BE junction may BE open.
Phi method of signal injection.
Add the signal source to the input end, and then measure the waveform at each point in turn to see if it is normal to find the fault point.Sometimes we will use a simpler method, such as holding a pair of tweezers to touch the input at all levels to see if the output side is responsive, which is commonly used in amplifying circuits such as audio, video, etc. (however, it should be noted that the circuit of hot baseplate or circuit with high voltage cannot be used, otherwise it may cause electric shock).If there is no reaction at the first level, and there is reaction at the second level, then the problem is at the first level, which should be checked.
There are many other ways to look, listen, smell, touch and so on.
"To see" is to see if the components have obvious mechanical damage, such as rupture, blackening, deformation, etc."Listening" refers to listening to whether the work sound is normal, such as something that shouldn't be loud, where it should be quiet or the sound is abnormal.Smell is to check for odors, such as the smell of burnt, capacitor electrolyte, etc.