Signal injection method

Signal injection method is more troublesome than measuring voltage. In transmitting the signal source to the input end, we need to measure the waveform of each subsequent point in order to find the fault point from the waveform. Of course, tweezers can also be used to detect the input end, the practice is to touch the input end with tweezers, and then observe the response of the input end, generally this method is used in the case of audio and video amplification circuit (note: hot floor circuit and high voltage circuit do not use this method, prone to electric shock accident). This method detects that the first stage is normal and the second stage is responsive, so the fault is not at the latter stage, but at the former stage.

Troubleshooting method 3: other

Whether it is a board made by others or a PCB board designed and made by yourself, the first thing to do is to check the integrity of the board, such as tin plating, cracks, short circuit, open circuit and drilling problems. If the role of the board is more rigorous, then you can check the resistance value between the power supply and the ground wire.

In general, the plate made by yourself will be installed on the components after tin plating is completed, and if people make it, it is just an empty shell of tin-plated PCB board with holes, and you need to install the components yourself when you get it. Some people for their own design of the PCB board has a larger information, so like to put all the components on the first time before testing, in fact, it is best to suggest a bit by bit.
Debug the PCB circuit board

New PCB board debugging can start from the power supply. The safest way to do this is to use a fuse and then connect to the power supply (it’s best to use a voltage regulator just in case). The regulated voltage power supply is set to be better than the current protection current, and then the regulated voltage power supply voltage is slowly raised upward. This process requires monitoring the input current, input voltage and output voltage of the board.

When the voltage goes up in the process, there is no over-current protection and the output voltage is normal, then, it means that there is no problem with the power supply part of the board, if it exceeds the normal output voltage or over-current protection, then it is necessary to troubleshooting the cause of the fault.
CPB circuit board components installation

In the debugging process, the modules are gradually installed, and each module or several modules are tested in accordance with the above steps, which is conducive to avoid some relatively hidden errors in the design of the first stage, or the installation of components errors, which lead to over-current burn components.

In case of failure in the installation process, the following methods are generally used to troubleshoot:

Fault troubleshooting method 1: voltage measurement method
Measuring voltage method

In case of over-current protection, do not remove components in a hurry. First, make sure the power pin voltage of each chip is within the normal range. Then the reference voltage and working voltage are tested in turn. For example, when silicon triode is on, the voltage of BE junction will BE around 0.7v, while that of CE junction is generally 0.3v or less. When it is found that the junction voltage of BE is higher than 0.7v during the test (darlington and other special tertiary tubes are excluded here), it may BE that the junction is open. The fault can be eliminated by checking the voltage of each point in turn.

Fault troubleshooting method 2: signal injection method

PCB board appearance inspection machine

The above two methods are relatively simple and direct. In addition, for example, the commonly said methods of seeing, smelling, listening, and touching need some experience before engineers can detect problems. Generally, “look” is not to see the status of the detection instrument, but to see whether the appearance of the components is complete; “Smell” is mainly to smell whether the smell of components is abnormal, such as the smell of burning, electrolyte, etc., generally components will send out a bad smell of burning when damaged.

“Listen” is mainly to listen to the working state of the sound of the board is normal; About “touch”, it is not to touch whether the component is loose, but to feel whether the temperature of the component is normal with the hand. For example, under the working state, the cold component is hot, while the hot component is unusually cold. Do not knead directly with the hand in the process of touching, in case the temperature is too high to burn the hand.