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How to debug a new circuit board?
- May 16, 2017 -

For a newly designed circuit boards, debugging can often encounter some difficulties, especially when the board is relatively large, more often than the components. But if you grasp a reasonable set of debugging methods, debugging will be more effective.

For the newly brought back the PCB board, we should first probably look at the board whether there is a problem, such as whether there is a clear rift, there is no short-circuit, open-circuit phenomena. If necessary, you can check the power supply with the grounding resistance is large enough.

Then the components are installed. Independent modules, if you are not sure that they are working properly, it is best not to all installed, but part of the pack (for relatively small circuits, can be loaded at a time), so easy to determine the scope of the fault, lest to encounter problems when it is not.

Generally speaking, the power supply can be installed first, then the power to detect the output voltage is normal. If you do not have a lot of grasp when power on (even if there is a great grasp, also suggest you add a fuse, just in case), can consider using the current limiting function of the adjustable voltage regulator. The preset is better than the current, then the voltage regulator of the power supply is slowly upward, and the input current, input voltage and output voltage are monitored. If there is no problem of overcurrent protection, and the output voltage reaches normal, the power supply Section OK is indicated. Conversely, disconnect the power supply, find the point of failure, and repeat the above steps until the power supply is normal.

Next gradually install other modules, each installation of a modules, on the electric test, the power is also followed by the above steps to avoid design errors or/and installation errors caused by the flow of burnout components.

There are generally several ways to find a fault:

① measuring voltage method.

The first thing to confirm is that the voltage of the chip power pins are normal, and then check the various reference voltages are normal, and the operating voltage of each point is normal and so on. For example, the general Silicon triode conduction, be junction voltage in 0.7V, while the CE junction voltage is around 0.3V or less. If a transistor is a junction voltage greater than 0.7V (special triode, such as Darlington tubes, etc.), may be the open is a knot.

② signal injection method.

Add the signal source to the input, and then measure the waveform of each point in turn, to see if it is normal to find the point of failure. Sometimes we can use a simpler approach, for example, with a hand tweezers, to touch the input at all levels, see if the output side of the reaction, this in the audio, video and other amplifier circuits often used (but to note that the hot backplane circuit or voltage high circuit, can not use this method, otherwise can lead to electric shock). If the first A levels of the collision did not react, and the impact of the first level of response, then the problem is indicated at the top a, should focus on inspection.

③ of course, there are many other ways to find fault points, such as watching, listening, smelling, touching and so on.

"Look" is to see the components have no apparent mechanical damage, such as rupture, burn black, deformation and so on; "Listen" is to listen to work sound is normal, such as some should not ring things in the ring, the sound of the place is not loud or abnormal voice; Smell is to check whether there is a peculiar smell, such as burnt flavor, capacitance electrolyte flavor.

For an experienced electronic maintenance staff, these smells are very sensitive; Touch is to use your hands to test whether the temperature of the device is normal, such as too hot or too cold. Some power devices, the work will be heated, if the touch is cool, it can basically be judged that it does not work. But if it shouldn't be hot, or the hot place is too hot.

General power transistors, voltage regulator chips, and so on, work under 70 degrees is totally no problem. What is the concept of a 70 degrees? If you put your hands up, you can stick to it for more than three seconds, the temperature is probably below 70 degrees (notice to try to feel the first tentative, don't burn your hands).