New PCB board debugging methods and experience summary
Summary of content: 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 reasonable set of debugging methods, debugging will be more effective. For a new PCB board that has just been returned, we must first roughly observe whether there are problems on the board, such as whether there are obvious cracks, whether there are short circuits, open circuits, and so on. If necessary, you can check whether the resistance between the power supply and the ground is large enough.
Then install the components. Independent modules, if you are not sure that they work properly, it is best not to install them all, but install them part by part (for smaller circuits, you can install them all at once), so that it is easy to determine the fault scope, When you get a problem, you ca n’t get started. Generally, 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 are not very sure when powering on (even if you are very sure, it is recommended that you add a fuse in case), you can consider using an adjustable regulated power supply with current limiting function. First preset the overcurrent protection current, and then slowly increase the voltage value of the regulated power supply, and monitor the input current, input voltage, and output voltage. If during the upward adjustment process, no problems such as overcurrent protection occur and the output voltage has reached normal, then the power supply part is OK. Otherwise, disconnect the power source, find the fault point, and repeat the above steps until the power source is normal.
Next, gradually install other modules. After each module is installed, power on and test it. Follow the above steps when powering on to avoid overcurrent and burnout of components due to design errors or / and installation errors.
There are several ways to find faults:
①Measure voltage method. The first thing to check is whether the voltage of the power pins of each chip is normal, then check whether the various reference voltages are normal, and whether the working voltage at 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, etc.), the BE junction may be open.
②Signal 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 a simpler method, such as holding a pair of tweezers with your hand, and touching the input terminals of each level to see if there is a response at the output terminal. This is often used in audio, video and other amplifier circuits (but note that the hot backplane Circuit or high voltage circuit, this method can not be used, otherwise it may cause electric shock). If there is no response at the previous level and there is a response at the next level, it means that the problem lies in the previous level and should be checked.
③ Of course, there are many other ways to find the fault point, such as watching, listening, smelling, and touching. "Seeing" is to see whether there is obvious mechanical damage to the component, such as cracking, burning, deformation, etc .; "Listening" is to hear whether the working sound is normal, for example, something that shouldn't beep is sounding, the place that should beep is not sounding or sound Abnormal, etc .; "smell" is to check whether there are any odors, such as the smell of burnt, the smell of capacitor electrolyte, etc. For an experienced electronic maintenance personnel, these odors are very sensitive; "touch" is to use Try to test whether the temperature of the device is normal, such as too hot or too cold. Some power devices will heat up when they are working. If they are cold to the touch, you can basically judge that they are not working. But if the place that shouldn't be hot is too hot or the place that is too hot is too hot, that's not enough. General power transistors, voltage regulator chips, etc., working under 70 degrees is completely fine. What is the concept of 70 degrees? If you press your hand up, you can hold it for more than three seconds, which means that the temperature is about 70 degrees or less.
Well, we have talked so much about debugging for today. If you want to learn more about debugging methods and experience, you can find some home appliance repair books. A good designer should first be A good maintenance person.