For a new design of the circuit board, debugging will often encounter some difficulties, especially when the board is larger, more components, often do not start. But if you master a reasonable debugging method, debugging will be twice the result with half the effort.
For the new PCB board we just got back, we should first roughly observe whether there is any problem on the board, such as whether there is obvious crack, 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.
Then it’s time to install the components. Independent modules, if you do not have the assurance that they work properly, it is better not to install all, but part of the installation (for smaller circuits, can be installed all at once), so that it is easy to determine the fault range, so that when encountering problems, do not know how to start. Generally speaking, the power part can be installed first, and then on to check whether the power output voltage is normal. If you don’t have much confidence in the power supply (even if you do, it is recommended that you add a fuse, just in case), consider using an adjustable voltage regulator with current limiting function. Firstly, the protection current is set above the current, and then the voltage value of the stabilized voltage supply is gradually increased, and the input current, input voltage and output voltage are monitored. If there are no overcurrent protection problems in the process of upward adjustment, and the output voltage reaches normal, then the power supply is OK. Otherwise, disconnect the power supply, find fault points, and repeat the above steps until the power supply is normal.
Next, install other modules gradually. Each time a module is installed, power it up and test it. Follow the above steps when power it up to avoid burning out the components due to overcurrent caused by design errors or/and installation errors.
Generally, there are several ways to find faults:
(1) measurement voltage method.
The first thing to confirm is whether the voltage of each chip power pin is normal, and then check whether the various reference voltage is normal, in addition to the point of the working voltage is normal. For example, when conducting a conventional silicon triode, 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 an audion is greater than 0.7v (except for special transistors such as darlington etc.), it is likely that the BE junction will open.
(2) signal injection method.
Add the signal source to the input end, and then measure the waveform of each point in turn to see if it is normal, so as to find the fault point. Sometimes we will use a simpler method, such as holding a tweezer, to touch the input end of all levels to see whether the output end is responsive, which is often used in audio, video and other amplifying circuits (but it should be noted that this method cannot be used in circuits with hot bottom plate or with high voltage, otherwise it may cause electric shock). If there is no reaction at the first level, but there is reaction at the second level, then the problem is at the first level and should be checked.
Of course, there are many other ways to find fault points.
Such as seeing, hearing, smelling, touching, etc. “To see” means to see if there is any obvious mechanical damage to the components, such as cracking, blackening, deformation, etc. “Listen” is to listen to whether the working sound is normal, such as some things should not ring, should not ring where the sound is not normal; “Smell” is to check whether there are odors, such as the smell of burnt, capacitor electrolyte, etc., for an experienced electronic maintenance personnel, is very sensitive to these odors; To “touch” is to use the hand to test whether the temperature of the device is normal, such as too hot or too cold. Some power devices, when working heat, if the touch is cool, you can basically judge that it does not work. But not if it’s too hot where it shouldn’t be or too hot where it should be. General power transistor, voltage regulator chip, etc., working under 70 degrees is no problem. What does 70 degrees look like? If you press your hand up and hold it for more than three seconds, the temperature is probably below 70 degrees.