How to Debug a Newly Developed Circuit Board?

For a newly designed circuit board, it is often difficult to debug it, especially when the board is relatively large and there are many components, it is often impossible to start. But if you master a reasonable set of debugging methods, debugging will be more effective.

For the new PCB board that has just been taken back, we must first observe whether there are problems on the board, such as whether there are obvious cracks, whether there are short circuits, open circuits, etc. If necessary, check whether the resistance between the power supply and the ground wire is large enough.

Then it’s time to install the components. Modules that are independent of each other, if you are not sure to ensure that they work normally, it is best not to install them all, but to install them part by part (for relatively small circuits, you can install them all at once), so that the fault range can be easily determined. When you encounter problems when you get it, there is no way to start.

Generally speaking, you can install the power supply part first, and then power on to check whether the output voltage of the power supply is normal. If you are not too sure about power up (even if you are sure, it is recommended that you add a fuse, just in case), consider using an adjustable regulated power supply with current limiting function. First preset the overcurrent protection current, then slowly increase the voltage value of the regulated power supply, and monitor the input current, input voltage and output voltage. If there are no problems such as overcurrent protection during the upward adjustment process, and the output voltage also reaches normal, then the power supply part is OK. On the contrary, it is necessary to disconnect the power supply, find the fault point, and repeat the above steps until the power supply is normal.

Next, install other modules gradually. After each module is installed, power on and test it. When powering on, follow the above steps to avoid overcurrent and burn out components due to design errors or/and installation errors. 

There are several ways to find faults:

①Measurement Voltage Method

The first thing to confirm is whether the voltage of the power supply pins of each chip is normal, and then check whether the various reference voltages are normal, and whether the working voltage of each point is normal, etc. For example, when a general silicon triode is turned on, the BE junction voltage is around 0.7V, while the CE junction voltage is around 0.3V or less. If the BE junction voltage of a triode is greater than 0.7V (except for special triodes, such as Darlington tubes, etc.), it may be that the BE junction is open.

②Signal Injection Method

Add the signal source to the input terminal, and then measure the waveform of each point in turn to see if it is normal, so as to find the fault point. Sometimes we also use simpler methods, such as holding a tweezers by hand, to touch the input terminals of all levels to see if the output terminals respond, which is often used in audio, video and other amplification circuits (but pay attention to the This method cannot be used for circuits with high voltage or high voltage circuits, otherwise it may cause electric shock). If there is no response at the previous level, but there is a response at the next level, it means that the problem lies in the previous level and should be checked.

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

"Looking" is to see whether there is obvious mechanical damage to the components, such as cracking, blackening, deformation, etc.; "Listening" is to listen to whether the working sound is normal, such as some things that should not be ringing, the place where the sound should be heard No sound or abnormal sound, etc.; "smell" is to check whether there is any odor, such as the smell of burning, the smell of capacitor electrolyte, etc.

For an experienced electronic maintenance personnel, it is very sensitive to these odors; "touching" is to test whether the temperature of the device is normal, such as too hot or too cold. Some power devices will heat up when they work. If they feel cool to the touch, it can basically be judged that they are not working. But it doesn't work if the place that shouldn't be hot is hot or the place that should be hot is too hot.

General power transistors, voltage regulator chips, etc., work under 70 degrees is completely no problem. What kind of concept is 70 degrees? If you press your hand up and you can hold it for more than three seconds, it means that the temperature is probably below 70 degrees (be careful to touch it tentatively first, and don't burn your hand).