PCB board debugging method

For the new PCB board , we must first observe whether there are any problems on the board, such as whether there are obvious cracks, short circuit or open circuit. If necessary, check if the resistance between the power supply and the ground is large enough.

For a newly designed circuit board, it  often encounters some difficulties when debugging, especially  large and big quantity components, it is often impossible to start. But if you master a reasonable set of debugging methods, it will be more effective for debugging

PCB board debugging steps

1. For the new PCB board that has just been taken back.If necessary, check if the resistance between the power supply and the ground is large enough.

2. Then install the components. Modules that are independent of each other, if you are not sure that they are working properly, it is best not to install them all but just some part (for smaller circuits, you can install them all at once), so that it is easy to determine the fault range.

In general, you can install the power supply firstly, and then power on to check if the power supply output voltage is normal. If you don't have much certainty when powering up (even if you have great confidence, it is recommended to add a fuse, just in case), consider using an adjustable regulated power supply with current limiting.

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 is no overcurrent protection and other problems during the upward adjustment, and the output voltage is also normal, the power supply is OK. Otherwise, disconnect the power supply, look for the key point of failure, and repeat the above steps until the power is normal.

2. Next, gradually install other modules. Each time a module is installed, power on to test. When powering up, follow the above steps to avoid over-current and burn out components due to design errors or/and installation errors.

Looking for a faulty PCB board

A. Measuring voltage method to find faulty PCB board

The first thing to confirm is whether the voltage of each chip's power supply pin is normal, and then check whether the various reference voltages are normal, and whether the working voltage of each point is normal. For example, when a 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 the BE junction voltage of a triode is greater than 0.7V (except for special triodes, such as Darlington), it may be that the BE junction is open.

B.Signal injection method to find faulty PCB board

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 fault point. Sometimes we will use simpler method, for example, holding a dice by hand, touching the input end of each stage to see if the output reacts, which is often used in audio, video and other amplifier circuits (but note that the circuit of the hot backplane or the circuit with high voltage, this method cannot be used, otherwise it may cause an electric shock). If there is no reaction at the previous level and there is a reaction at the next level, the problem is at the previous level and should be checked.

C. Other methods for finding faulty PCB boards

There are many other ways to find fault points, such as watching, listening, smelling, and touching.

"Watching" is to see if the component has obvious mechanical damage, such as cracking, blackening, deformation, etc.;

"Listening" means listening to whether the working voice is normal. For example, some things that should not be ringing are ringing, the place where the ringing is not ringing or the sound is not normal, etc.;

"Smell" is to check for odor, such as the smell of charred, the taste of the capacitor electrolyte, etc., which is very sensitive to an odor for an experienced electronic maintenance person;

“Touch” is to test the temperature of the device by hand, such as too hot, or too cold.Take precautions when you touch, safety is the most important thing.

Some power devices will generate heat when they work. If they are cold, they can basically be judged that they are not working. But if the hot place is not hot or the hot place is too hot, it will not work. General power triodes, voltage regulator chips, etc., working below 70 degrees is completely fine.