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How to debug a new designed circuit board

  Time:2017-10-17 11:04
For a new design of the circuit board, debugging 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 the problems on the PCB board, such as whether there are obvious cracks, whether there is short circuit or open circuit and so on. If necessary, check whether the resistance between the power line and the ground wire is large enough.
And then you install the 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. Generally speaking, the power part can be installed first, and then the power supply is tested to check whether the output voltage is normal. If you are not very sure when you power up (even if you have a lot of confidence, also suggest you add a fuse, just in case), you can consider using the current limiting function of the adjustable voltage regulator. The voltage current of the regulated power supply is slowly raised, and the input current, the input voltage and the output voltage are monitored. If you go up in the process, there have been no problems of current protection, and the output voltage has reached normal, the power supply part of the OK. on the other hand, is to cut off the power, to find the point of failure, and repeat the above steps until the power supply is normal so far.
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 several ways to find fault:

Measuring voltage method. First of all to confirm the voltage of each chip power supply pin is normal, and then check whether the reference voltage is normal, in addition to each point of the work voltage is normal, etc.. For example, when the general silicon triode is conducted, 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 a triode is greater than 0.7V (except for the special transistor, such as Darlington Transistor), it is possible that the BE junction is open.
Signal injection method. The signal source is added to the input end, and then the waveform of each point is measured backward to see if it is normal, so as 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 level, and after the first level of reaction, it shows that the problem is in the first level, should focus on inspection.
And, 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 staff, the smell is very sensitive: "touch" is by hand to test the temperature of the device is normal, such as too hot or too cold. Some power devices work when they're heated, and if it's cold, it's basically judged that it doesn't work. But if the heat is not hot, or the heat is too hot, that's not enough. The general power transistor, regulator chip, etc., work below 70 degrees is no problem. What kind of concept is 70 degrees? If you put your hand on it, you can hold it for more than three seconds, which means that the temperature is about 70 degrees.