How many common PCB debugging skills do you possess?
How many common PCB debugging skills do you possess?
Whether you had a PCB made by someone else or designed and built your own, the first thing to do upon receiving it is to check its integrity, such as for issues like tin plating, cracks, short circuits, open circuits, and drilling holes. If the board's function is critical, you can also check the resistance between the power supply and ground lines.
Generally, DIY PCBs have components installed after tin plating, while a custom-made PCB is just an empty tin-plated shell with holes, requiring you to install components yourself upon receiving it.
Some people have a lot of confidence in their PCB design and like to install all components at once before testing. However, it's generally recommended to proceed step by step.
Debugging a new PCB can start with the power supply. The safest method is to install a fuse and then connect the power supply (preferably a regulated power supply as a precaution).
Use a regulated power supply, set the overcurrent protection current, and then slowly increase the voltage. During this process, monitor the board's input current, input voltage, and output voltage.
If no overcurrent protection triggers and the output voltage remains normal during voltage adjustment, the power supply section of the board is likely functioning correctly. However, if the output voltage exceeds the normal range or overcurrent protection is triggered, the cause of the fault needs to be investigated.
During the debugging process, gradually install the modules, following the above steps for testing after each module or several modules are installed. This helps avoid subtle design errors or incorrect component installation that could lead to overcurrent damage.
If a fault occurs during installation, the following methods are generally used for troubleshooting:
Troubleshooting Method 1: Voltage Measurement Method When overcurrent protection occurs, do not rush to remove components. First, check the voltage of each chip's power supply pin to see if it is within the normal range. Then, check the reference voltage, operating voltage, etc., in sequence.
For example, when a silicon transistor is conducting, the voltage at the BE junction will be around 0.7V, while the CE junction is generally 0.3V or lower.
If the BE junction voltage is found to be higher than 0.7V during testing (excluding special transistors such as Darlington transistors), then the BE junction may be open. By checking the voltage at each point using the same method, the fault can be eliminated. Troubleshooting Method Two: Signal Injection Method Signal Injection Method The signal injection method is more complicated than measuring voltage. After sending the signal source to the input terminal, we need to measure the waveform at each subsequent point in sequence to find the fault point.
Alternatively, tweezers can be used to test the input terminal. The method involves touching the input terminal with tweezers and observing the response. This method is generally used in audio/video amplifier circuits (Note: Never use this method in hot-ground circuits or high-voltage circuits, as it can easily cause electric shock).
If this method detects that the previous stage is normal, but the next stage responds, then the fault is not in the next stage, but in the previous stage.
Troubleshooting Method Three: Other PCB Circuit Board Appearance Inspection Machine The above two methods are relatively simple and direct. Other methods, such as looking, smelling, listening, and touching, require experienced engineers to detect problems.
Generally, "looking" doesn't refer to checking the condition of the testing equipment, but rather to inspecting the external appearance of the components for completeness. "Smelling" mainly involves checking for any abnormal odors from the components, such as burnt smells or electrolyte odors; damaged components typically emit an unpleasant burnt smell.
"Listening" primarily involves listening to the sound of the board during operation to ensure it sounds normal. "Touching" doesn't mean checking for looseness, but rather feeling the temperature of the components to ensure it's within acceptable limits. For example, during operation, components that should be cool might be hot, while components that should be hot might be abnormally cold. When touching components, never squeeze them directly with your hands to avoid burns from excessive heat.
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