For a newly designed circuit board template, debugging will often encounter some difficulties, especially when the board is larger, more components, often do not know where to start. But if master a set of reasonable debugging methods, debugging will be twice the result with half the effort.
PCB sample debugging generally follows the following steps:
1. PCB board surface observation and resistance inspection between power supply and ground wire
As for PCB sample making, we should first roughly observe whether there are problems on the board, such as whether there are obvious cracks, whether there is a short circuit, open circuit and other phenomena. If necessary, check that the resistance between the power supply and the ground wire is large enough.
Install components
Then it’s time to install the components. Independent modules, if you are not sure to ensure that they work properly, it is best not to install all of them, but a part of a part of the installed (for a smaller circuit, can be installed all at once), it is easy to determine the PCB fault range, so as not to encounter problems, do not start.
Check whether the output voltage of the power supply is normal
Generally speaking, the power supply can be installed first, and then on the power supply output voltage is normal. If you are not too sure when power on (even if you are very sure, it is recommended that you add a fuse, just in case), you can consider using an adjustable voltage regulator with current limiting function.
4. Preset overcurrent protection current
The voltage value of the stabilized power supply is gradually increased and the input current, input voltage and output voltage are monitored. If there is no current protection and the output voltage is normal in the process of up-regulation, the power supply part is OK. Instead, disconnect the power, look for fault points, and repeat the steps until the power is normal.
Install other modules and test them on power
Next, install the other modules gradually. Each module is installed, test the power on, and when the power on, also follow the steps above, to avoid the design error or component installation error caused by excessive flow and burning out the components.
There are generally several ways to find PCB faults:
I. voltage measurement method
The first thing to confirm is whether the voltage of each chip power pin is normal, then check whether all kinds of reference voltage is normal, in addition to the operating voltage of each point is normal. For example, when a typical silicon transistor is conducting, 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 triode is greater than 0.7v (except for special triodes, such as darlington tube, etc.), the BE junction may BE open.
Ii. Signal injection method
Add the signal source to the input end and then measure the waveform of each point to see if it is normal to find the PCB fault point. Sometimes we also use a simpler method, such as holding a tweezer in hand, to touch the input end of each level, to see whether the output end has a reaction, which is often used in audio, video and other amplifier circuits (but be aware that the hot plate of the circuit or circuit with high voltage, can not use this method, otherwise it may lead to electric shock). If there is no reaction in the previous level, and there is a reaction in the next level, it indicates that the problem is in the previous level, should focus on inspection.
Of course, there are many other ways to find PCB fault points, such as looking, listening, smelling, touching and so on
“See” is to see whether the component has obvious mechanical damage, such as rupture, blackening, deformation, etc.; “Listen” is to listen to the working sound is normal, for example, some things should not ring in the ring, the ring place does not ring or the sound is not normal; “Smell” is to check whether there is a peculiar smell, such as the smell of burning, the smell of capacitor electrolyte, etc., for an experienced electronic maintenance personnel, to these smells is very sensitive; To “touch” means to test whether the temperature of the device is normal, such as too hot or too cold. Some power devices, when working heat, if it is cool to the touch, it can be basically judged that it is not working. But if it’s hot where it shouldn’t be, or if it’s too hot where it should be, it won’t work. General power triode, voltage regulator chip, etc., work in 70 degrees is completely no problem. What does 70 degrees look like? If you press your hand up, hold for more than three seconds, and the temperature is below 70 degrees.