How to debug a new circuit board?

- May 26, 2017-

For a new design of the circuit board, debugging often encounter some difficulties, especially when the board is relatively large, more components, often unable to start. But if you master a reasonable set of debugging methods, debugging will be more with less.

    For just come back to the new PCB board, we must first look at the board, whether there is a problem on the board, such as whether there are obvious cracks, with or without short circuit, open circuit and so on. If necessary, you can check whether the resistance between the power supply and the ground is large enough.

    Then is the installation of the components. Independent of the module, if you do not grasp to ensure that they work properly, it is best not to all installed, but part of the installation (for a relatively small circuit, you can all installed), so easy to determine the fault range, Free to encounter problems, no way to start.

    In general, you can put the power part of the first installed, and then power on the detection power supply output voltage is normal. If you do not have much control at power-up (even if you have a great deal of confidence, it is recommended that you add a fuse, just in case), consider using a regulated power supply with current limiting. First set the current overcurrent protection current, and then the voltage regulator voltage slowly to increase, and monitor the input current, input voltage and output voltage. If the process of upward, there is no over-current protection and other issues, and the output voltage has reached a normal, then the power section OK. Instead, turn off the power, find the point of failure, and repeat the above steps until the power is normal.

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

    Find the fault of the general approach are the following:

    Measurement voltage method.

    First of all to confirm that the chip power supply pin voltage is normal, followed by a variety of reference voltage to check whether the normal, in addition to the point of the work voltage is normal and so on. For example, when the general 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 a transistor's junction voltage is greater than 0.7V (except for special triode, such as Darlington tube, etc.), it is possible that the BE junction is open.

    ② signal injection method.

    Add the signal source to the input, and then measure the waveforms of each point in turn to see if they are normal to find the point of failure. Sometimes we will use a more simple way, such as hand holding a tweezers, to touch the input at all levels to see whether the output response, which in audio, video and other amplifiers often used (but note that the hot floor Circuit or high voltage circuit, can not use this method, otherwise it may cause electric shock). If the first level did not respond, and touch a response, then the problem in the previous level, should focus on inspection.

③ Of course, there are many other ways to find the point of failure, such as watching, listening, smell, touch and so on.

    "Listen" is to see whether there is any obvious mechanical damage to the component, such as rupture, burning black, deformation, etc .; "listen" is to listen to the work of the sound is normal, for example, something should not ring in the ring, the ring does not ring or sound Abnormal, etc .; "smell" is to check whether there is odor, such as charred taste, the smell of capacitive electrolyte and so on.

    For an experienced electronic maintenance personnel, it is very sensitive to these scents; "touch" is to test the temperature of the device is normal, such as too hot, or too cold. Some power devices, work together will be hot, if the touch is cool, you can basically judge it did not work up. But if the hot place is not hot or the hot place is too hot, it is not enough.

    General power transistor, regulator chip, etc., work in the following 70 degrees is completely no problem. 70 degrees is probably a concept? If you hand pressure up, you can adhere to more than three seconds, it means that the temperature is about 70 degrees below (pay attention to the first tentative to touch, do not burn your hands).

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