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During the process of debugging a new circuit board design, we often encounter some difficulties, especially when the circuit board is large and has long components, and the startup may encounter obstacles. However, if a scientific and reasonable debugging process can be mastered, the effectiveness of debugging work will be significantly improved.
For newly arrived PCBs, the first task is to check whether there are defects on the board, such as obvious cracks, short circuits, open circuits, etc. If necessary, check whether the resistance value between the power line and the ground wire meets safety standards.
Next comes the installation phase of the components. For stand-alone modules, if you are not sure whether they will work properly, it is recommended not to install all the equipment at once, but to install it partially (for circuits, it can be a smaller complete part), so that the scope of the fault and the problem can be easily determined, especially when you don’t know where to start.
Usually, you can install the power supply first, and then test the power supply after powering on to confirm whether the output voltage is normal. Even if you have full confidence, it is recommended to add a fuse to prevent accidents. It is recommended to use an adjustable voltage power supply with a current-limiting function. The pre-set current value should be higher than the current protection value, and the voltage of the voltage-stabilized power supply should be slowly increased while monitoring the input current, input voltage, and output voltage. If there is no overcurrent protection trigger and the output voltage reaches the normal level, the power supply part can be considered qualified. After that, the power supply should be disconnected, the fault point should be found, and the above process should be repeated until the power supply part is completely normal.
Then, install other modules step by step, ensuring that each module is installed correctly, power-on testing, and following the power check steps above to avoid overcurrent and component damage due to design or installation errors.
First, confirm whether the voltage of each chip power pin is normal, then check whether the reference voltage is 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 lower. If the BE junction voltage of the transistor is greater than 0.7V (except for special transistors such as Darlington transistors, etc.), the BE junction may be disconnected.
Connect the signal source to the input terminal and measure the waveform of each point in turn to determine whether it is normal, to find the fault point. Sometimes we use a simple method, such as using tweezers to touch each layer to observe whether there is an output response in the audio and video amplifier circuit (but it should be noted that this method should not be used for heating circuits or high-voltage circuits to avoid the risk of electric shock). If there is no response at the first level, but there is a response at the second level, it means that the problem lies in the previous level, which should be the focus of the inspection.
Naturally, there are many ways to explore the problem, including the use of vision, hearing, smell, touch, and other senses. In terms of observation, the main thing is to check whether there is obvious mechanical damage, such as cracks, burns, or deformation; in terms of hearing, the main thing is to determine whether the sound of the equipment is normal when it is running, such as whether there are parts that should not make sounds or abnormal sounds; in terms of smell, the main thing is to detect whether there are abnormal odors, such as the smell of electrolyte or capacitors.
Experienced electronic repair personnel are particularly sensitive to these odors; in terms of touch, they can test the temperature of the device by touching it, such as whether the device is overheated or overcooled. Some power devices generate heat when working. If the device temperature feels low, it may indicate that the device is not working properly. However, if the device temperature is not obvious or overheated, such information is not enough to make an accurate judgment.