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How to debug the new circuit board?

Release Date:2020-02-24

For a newly designed circuit board, it is often difficult to debug, especially when the board is large and the components are relatively large. But if we master a reasonable set of debugging methods, we will get twice the result with half the effort.

For the new PCB board that we just brought back, we should first look at whether there are any problems on the board, such as whether there are obvious cracks, whether there is short circuit or open circuit. If necessary, check whether the resistance between the power ground and the ground wire is large enough.

Then we install the components. Mutually independent modules, if you are not sure that they are working properly, it is best not to install all of them, but to install a part of them (for a relatively small circuit can be installed all at once), so that the scope of the fault can be easily determined, and no problem can be avoided when there is a problem.

Generally speaking, the power supply part can be installed first, and then the power is detected to check whether the output voltage of the power supply is normal. If you are not too sure about the power on (even if you have a great deal of assurance, you are advised to add a fuse, just in case), consider the use of adjustable voltage stabilizer with current limiter. First, the current is protected by the current, then the voltage value of the regulated power supply is slowly increased, and the input current, input voltage and output voltage are monitored. If there is no overcurrent protection during the up regulation process, and the output voltage is also normal, the power supply part OK will be explained. Instead, disconnect the power supply, locate the fault points, and repeat the above steps until the power supply is normal.

Then gradually install other modules, each installed a module, the power on the test, power up is also in accordance with the above steps, in order to avoid the design error or / and installation error caused by overflowing and burned components.

There are usually several ways to find fault.

1.Measuring voltage method.

First of all, we need to confirm whether the voltage of the power supply pin of each chip is normal, then check whether the reference voltage is normal, and whether the working voltage of each point is normal. For example, when the silicon transistors are switched on, the BE junction voltage is about 0.7V, while the CE junction voltage is about 0.3V or smaller. If the BE junction voltage of a triode is greater than 0.7V (except for special triode, for example, Darlington tube, etc.), it may be that the BE junction opens.

2.Signal injection method.

The signal source is added to the input port, and then the waveforms of each point are measured in turn to see if it is normal to find the fault point. Sometimes we will use a simpler method, such as holding a tweezers to touch the inputs at all levels to see if the output is responsive. This is often used in audio, video and other amplifying circuits. If there is no reaction at the first level before the collision, and there is reaction at the second level after the collision, it means that the problem is at the first level, and the inspection shall be focused on.

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

"Look" is to see whether the components have obvious mechanical damage, such as breakage, blackening, deformation, etc.; "listen" is to hear whether the working sound is normal, for example, some things that should not be heard are ringing, the place where the sound is not or the sound is abnormal, etc.; "smell" is to check whether there is abnormal smell, such as the smell of burning, the smell of capacitor electrolyte, etc.

For an experienced electronic maintenance worker, it is very sensitive to these odors. "Touch" means using the hand to test whether the device's temperature is normal, such as too hot or too cold. Some power devices will work when they work. If they feel cool, they can basically be judged that they are not working. But if the heat is not hot or the hot area is too hot, that will not do.

The general power triode, voltage regulator chip and so on, working below 70 degrees is no problem at all. What is the concept of 70 degrees? If you press your hand up, you can hold it for more than three seconds. It means that the temperature is below 70 degrees.

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