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For a newly designed circuit board, debugging often encounters with some difficulties, especially when the board is large and there are many components, it is often hard to start. But if you got some reasonable methods, debugging will be more effective.

PCB debugging step 1:

For the new PCB we got back, first we must observe whether there are any problems on the board or not, such as obvious cracks, short circuit or open circuit. If necessary, check if the resistance between the power supply and the ground is large enough.

PCB debugging step 2:

Then comes to the component assembly. Independent modules, if you are not sure that they are working properly, do not assemble them all, but assemble some of them step by step (for smaller circuits, you can finish them all at once), so it is easy to confirm the failure range, in case of do not know how to do it when problems happen.

Generally speaking, you can assemble the power supply first, and then power on to checkif the output voltage is normal. If you are not sure when powering on (even if you havegreat confidence in yourself, it is recommended to add a fuse, just in case), you can consider using an adjustable regulated power supply with current limiting.

First, preset the protection current for overcurrent, then slowly increase the voltage value of the powersupply, and monitor the input current, input voltage, and output voltage. If there is no over-current protection or other problems during the adjustment, and the output voltage is also normal, then the power supply is OK. Otherwise, cut off power supply,look for the point of failure, and repeat the steps above until the power supply turns intnormal condition.

PCB debugging step 3:

Next, gradually assemble other modules. Each time when a module is being assembled, power on and test it. When power on, follow the steps above to avoid over-current toburn out components due to the design errors or assembly errors.

There are several ways to find out the bugs:

①. Voltage measurement. First you need to confirm if the pin voltage of each power chipis normal, and then check if the various of reference voltages are normal, and if the working voltage of each point is normal. For example, when a silicon transistor is in conductive state, the BE voltage is about 0.7V, and the CE voltage is about 0.3V or less.If the BE voltage of a silicon triode is greater than 0.7V (except for special silicon triode, such as Darlington), then it may be the BE is open.

②. Signal injection. Add the signal source to the input end, and then measure the waveform of each point one by one to see if it is normal in order to find out the failure. Sometimes we will use a simpler method, such as holding a dice by hand, touching the input terminals of each pole to see if there is any reaction at the output end, which is often used in audio, video and other amplifier circuits (but note that the circuit of the hot backplane or circuit with heavy voltage cannot use this method, otherwise it may cause electric shock. If there is no reaction at the previous pole but next pole does, then the problem is at the previous pole and it should be checked.

③. Of course, there are many other ways to find out the bugs, like watching, listening, smelling, touching, etc. "watching" is to see if the component has obvious mechanical  damage, such as cracking, blackening, deformation, etc.; "listening" means listening to the working sound if it is normal, for example, something that should not ring but rings or the sound is unnormal; "smell" is to check for odor, such as the smell of burning, the chemicals of the electrolytic capacitance etc., for an experienced electronic maintenance personnel, he is very sensitive to these odors; "touch" is trying to use the hands to test if the temperature of the device is normal, such as overheat or too cold. Some power devices will generate heat when they work. If they are cold, then we can basically confirm that they are not working. For normal power silicone triodes, voltage regulator chips and other things, it's completely ok for them to work below 70 degrees. What is the concept of 70 degrees? If you press your hands up on it for more than 3 seconds, which means the temperature is under 70 degrees (note: touch it tentatively first, don't burn your hands).Ok, about the debugging problems, we will talk about it so much today. If you want to know more about the debugging methods and experience, you can look for some books on home appliance repair. A good designer should become a good maintenance person first.