PCB board debugging and finding faulty PCB board

PCB board debugging method

For the new PCB board we just got back, we should first roughly observe whether there are problems on the board, such as whether there are obvious cracks, whether there are short circuit, open circuit and other phenomena. If necessary, check that the resistance between the power supply and the ground wire is high enough.

For a new design of the circuit board, debugging will often encounter some difficulties, especially when the board is larger, more components, often do not know how to start. But if you master a set of reasonable debugging methods, debugging will get twice the result with half the effort.

PCB board debugging steps

1. For the new PCB board that has just been taken back, 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.

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 to install some of them (for smaller circuits, you can install them all at once), so that it is easy to determine the fault range. When you have problems when you are not getting it, you can't start.

In general, you can install the power supply first, and then power on to check if the power supply output voltage is normal. If you don't have much control when powering up (even if you have a great grasp, 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 point of failure, and repeat the above steps until the power is normal.

3. Next, gradually install other modules. Each time you install a module, you can test it on power. Follow the above steps when powering up to avoid over-current and burn out components due to design errors or/and installation errors.

Ways to find a faulty PCB board

1. 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.

2. Signal injection method to find faulty PCB board

Add the signal source to the input, and then measure the waveform of each point backwards to see if it is normal to find the fault point. Sometimes we will use a simpler method, such as holding a dice by hand, touching the input terminals of each level to see if there is any reaction at the output, which is often used in audio, video and other amplifier circuits (but note that the hot backplane This circuit cannot be used for circuits or circuits with high voltages, otherwise it may cause 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.

3. Other methods for finding faulty PCB boards

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

“Look” 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 burnt, the taste of the capacitor electrolyte, etc., which is very sensitive to an odor for an experienced electronic maintenance person;

"Touching" is to test the temperature of the device by hand, such as too hot, or too cold.

Some power devices 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 ok. What is the concept of 70 degrees? If you put your hand on it, you can stick it for more than three seconds, which means the temperature is about 70 degrees (be careful to test it first, don't burn your hand).