How to debug the new circuit board?

- Jul 05, 2017-

For a new design of the circuit board, debugging will often encounter some difficulties, especially when the board is relatively large, components are relatively long, often have no way to start. But if you master a reasonable set of debugging methods, debugging will be twice the result with half the effort.

For the new PCB board that we just got back, we should first look at it and see whether there are any problems on the board, such as whether there are obvious cracks, whether there is short circuit or open circuit or not. If necessary, check that the resistance between the power line and the ground wire is large enough.

Then there is the installation of components. Independent modules, if you are not sure that they work properly, not all the best of all equipment, but part of the mount (for the circuit can be a relatively small all installed), so easy to determine the scope of the fault and problem free by the time, do not know how to start.

In general, you can put the power part first installed, and then power on, detect the power supply, the output voltage is normal. If you are not too sure (even if you have a lot of confidence) on power up, it is recommended that you add a fuse, just in case). You may consider using an adjustable voltage power supply with current limiting function. The preset current is better than the current protection current, then the voltage of the regulated power supply is slowly raised, and the input current, the input voltage and the output voltage are monitored. If there is no over-current protection and so on, and the output voltage has reached normal, then the power supply section OK. Instead, disconnect the power source, look for the fault point, and repeat the procedure until the power is normal.

Then gradually install other modules, each module has a good installation, power on test, when the power is in accordance with the above steps, to avoid because of design errors and / or installation errors caused over-current and burned components.

There are usually several ways to find fault:

1. measuring voltage method.

First of all, to confirm the voltage of each chip power supply pin is normal, and then check the reference voltage is normal, in addition to each point of the work voltage is normal. For example, when the general silicon triode is switched on, the BE junction voltage is about 0.7V, while 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 a special triode, such as a Darlington transistor, etc.), it is possible that the BE junction will open.

2. signal injection method.

The signal source is added to the input, and then in turn to measure the waveform of each point, to see whether normal, in order to find the fault point. Sometimes we will use a more simple way, such as holding a tweezers, input to touch at all levels, to see whether the output response in the audio and video amplification circuit used in (but note that the bottom of the heat circuit or high voltage circuit, not the use of this method, or may cause an electric shock). If there is no reaction before the first strike, and after the first level of reaction, it shows that the problem is at the previous level, should be the focus of inspection.

3., of course, there are many other ways of looking for trouble spots, such as watching, listening, smelling, touching, etc..

"Look" is to see the element with no obvious mechanical damage, such as rupture, burning and deformation; "listen" is to listen to the voice work is normal, such as not the sound of things in the ring, the ring where not ring or sound is not normal; "smell" is to check whether there is peculiar smell, for example, the smell of burning smell and electrolyte capacitor.

For an experienced electronic maintenance worker, they are sensitive to these smells; "touch" is to test the temperature of the device by hand, such as too hot, or too cold. Some power devices work when they heat up. If it feels cool, it can basically be judged that it doesn't work. But if the heat is not hot, or the heat is too hot, that's not enough.

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