How to debug a new board

For the new PCB board we just came back, we must first observe if there are any problems on the board, such as whether there are obvious cracks, short circuits or open circuits. If necessary, check if the resistance between the power supply and ground is large enough.

There are several ways to find the fault:

1. measurement voltage method.

The first thing to confirm is whether the power supply pin voltage of each chip is normal, and then check whether the various reference voltages are normal and whether the operating voltage of each point is normal. For example, when a typical 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 the 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.

Add a signal source to the input and measure the waveform at each point in turn to see if the fault point is found to be normal. Sometimes we use an easier way, such as holding the dice by hand, touching the input terminals of each level to see if there is any reaction at the output, which is usually used for audio, video and other amplifier circuits (but please pay attention to the heat Backplane This circuit cannot be used in high voltage circuits or circuits, otherwise it may cause electric shock. If the previous stage does not react and the next stage reacts, the problem should appear in the previous stage.

 

3. Of course, there are many other ways to find fault points, such as watching, listening, smelling, touching, etc.

“Looking” refers to whether the component has obvious mechanical damage, such as cracking, blackening, deformation, etc. “Listening” means listening to the working sound is normal, for example, the sound should not be loud, the sound is not loud or the sound is not normal; The "smell" is to check the smell, such as the smell of burning, the taste of the capacitor electrolyte. "Touch" is the temperature of the device being tested by hand, for example too hot or too cold. Some power devices generate heat when they are working. If they are cold, they can basically judge that they are not working.