- By Measuring Voltage
The first thing to confirm is whether the voltage of each chip power pin is normal or not, then check whether the various reference voltage is normal or not, in addition to the point of the working voltage. For example, a typical silicon triode has a BE junction voltage of about 0.7V, and a CE junction voltage of about 0.3V or less.If the BE junction voltage of a transistor is greater than 0.7V (except for special transistors, such as darlington tube, etc.), the BE junction may open.
Will signal to input, and then in turn back to measure the waveform at every point, look to whether normal, to find the fault point we sometimes use more simple way, with a forceps in hand, for example, to touch at all levels of the input, the output side reaction, the amplifying circuit such as audio video often use (but note that hot plate or high voltage circuit, can’t use this method, otherwise it may lead to electric shock) if touch before level don’t respond, and touch after level 1, then the problem in the first level, should focus on inspection
Other methods to find defective PCB
There are many other ways to look for trouble spots, such as seeing, hearing, smelling, touching, etc.
1.”To see” means to see whether the component has obvious mechanical damage, such as rupture, blackening, deformation, etc.;
2.”Listen” is to listen to whether the work sound is normal, such as some shouldn’t sound things in the ring, the sound of the place is not sound or sound abnormal, etc.;
3.”Smell” is to check for odors, such as burning smell, the smell of capacitor electrolyte, etc., to an experienced electrical maintenance personnel, that is very sensitive to these smells;
4.To “touch” means to test the temperature of the device by hand to see if it is normal, such as too hot or too cold.
Some power devices, if they would be hot when working, if one touches that is cold, it can be basically judged that it does not work. But if it’s too hot where it shouldn’t be or too hot where it should be, that’s not going to work. General power transistor, voltage regulator chip, etc., working at 70 degrees below is completely no problem. What does 70 degrees look like? If you press your hand on it, you can hold it for more than three seconds, which means the temperature is below 70 degrees.