For a newly designed circuit board, debugging often encounters some difficulties, especially when the board is relatively large and there are many components, it is often impossible to start. But if you master a set of reasonable debugging methods, debugging will get twice the result with half the effort. For the new PCB board that has just been taken back, we must first roughly observe whether there are any problems on the board, such as whether there are obvious cracks, short circuits, open circuits, etc. If necessary, check whether the resistance between the power supply and the ground wire is large enough.
Then it is time to install the components. For independent modules, if you are not sure that they are working properly, it is best not to install all of them, but to install part by part. For relatively small circuits, you can install them all at once. So that it is easy to determine the fault range. Avoid having trouble getting started. Generally speaking, you can install the power supply first, and then power on to check whether the output voltage of the power supply is normal. If you do not have much confidence when powering up (even if you are sure, it is recommended that you add a fuse, just in case), you can consider using an adjustable regulated power supply with current limiting function. Preset the overcurrent protection current first, 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 over-current protection and other problems during the upward adjustment process, and the output voltage has reached normal, it means that the power supply is OK. Otherwise, disconnect the power supply, find the fault point, and repeat the above steps until the power supply is normal.
Next, install other modules gradually. Each time a module is installed, power on and test it. When powering on, follow the above steps to avoid over-current caused by design errors or installation errors and burn out components.
There are generally several ways to find faults:
① Measuring Voltage Method
The first thing to confirm is whether the voltage of the power supply pins of each chip 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, while the CE junction voltage is about 0.3V or less. If the BE junction voltage of a transistor is greater than 0.7V (except for special transistors, such as Darlington, etc.), it may be that the BE junction is open.
②Of course, there are many other ways to find fault points, such as watching, listening, smelling, touching, etc. “Watching” means to see if there is any obvious mechanical damage to the component, such as cracks, burns, deformation, etc. “Listen” means to hear whether the working sound is normal, for example, something that shouldn’t sound is sounding, and the place where it should sound is not loud or sound Abnormality, etc. “Smell” is to check for peculiar smells, such as burnt smells, capacitor electrolyte smells, etc. For an experienced electronics repairer, they are very sensitive to these smells. “Touching” means using hands to test whether the temperature of the device is normal, such as too hot or too cold. Some power devices generate heat when they work. If they are cold, it can basically be judged that they are not working. But if the place that shouldn’t be hot is hot or the place that should be hot is too hot, that won’t work either. General power transistors, voltage regulator chips, etc., working below 70 degrees is completely no problem. What is the approximate concept of 70 degrees? If you press your hand up and you can hold it for more than three seconds, it means that the temperature is below 70 degrees. Note that you must touch it tentatively first, and don’t burn your hands.
③Signal Injection Method
Add the signal source to the input terminal, and then measure the waveform of each point in turn to see if it is normal to find the fault point. Sometimes we also use simpler methods, such as holding a tweezers with our hands, touching the input terminals of all levels, to see whether the output terminal responds, this is often used in audio, video and other amplifier circuits. But note that the hot bottom plate circuits or high voltage, this method cannot be used, otherwise it may cause electric shock). If there is no response to the previous level, but there is a response to the next level, it means that the problem lies in the previous level and should be checked.
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