For new PCB just back, we will probably look at the first, whether there is a problem on board, such as whether there are obvious cracks, the phenomenon such as short circuit, open circuit. If necessary, you can check the power supply with ground resistance between is big enough.
And then there are the installed components. Independent modules, not sure if you keep them working properly, it's best not to install, all but part of part of the mount (for smaller circuit, can be a whole mount), so easy to determine the scope of the fault, lest meet with problems, do not know how to start. In general, you can put the power part of the first, and then to electricity detection power supply output voltage is normal. If you don't have too big hold when electricity (even if there is a lot of, also suggest you add a fuse, in case of a one thousand), consider using adjustable regulated power supply with current limiting function. Default is much better than current protection current first, and then the voltage stability of electric power supply voltage to increase slowly, and monitoring the input current, input voltage and output voltage. If the increase in the process of problem such as no over-current protection, and also reached the normal output voltage, shows the power part OK. On the contrary, should disconnect the power supply, to find fault point, and repeat the above steps, until the power supply is normal.
Then gradually to install other modules, each module is installed, the top electric test, when electricity is according to the above steps, in order to avoid because of design errors and/or installation errors caused by over current and burn out elements.
To find fault generally have the following:
1. Measure the voltage method. First to make sure the chip pins of the voltage is normal, then inspect all kinds of reference voltage is normal, and each point of the voltage is normal, etc. For example, the general silicon triode conduction, BE junction voltage at around 0.7 V, and the CE junction voltage at around 0.3 V or less. If a triode BE junction voltage is greater than 0.7 V (except for special triode, for example, darlington tube, etc.), and is likely to BE open.
2. the signal injection method. Will signal to input, and then in turn back to measure the waveform at every point, look to whether normal, to find the point of failure. Sometimes we will also use more simple way, with a forceps in hand, for example, to touch at all levels of the input, the output side reaction, which used in audio, video and other amplifier circuit (but note that hot plate or high voltage circuit, can't use this method, otherwise it may lead to electric shock). If touch before level don't respond, but touch after level 1, then the problem in the first level, should focus on inspection.
3. of course, there are many other to find the fault location method, for example, see, hear, smell, touch, etc. "Look" is to see elements have obvious mechanical damage, such as cracking deformation, blackened, such as: "listening" is to listen to the voice is normal work, such as some things shouldn't ring in the ring, the place is not rings or abnormal sound, such as: "smell" is to examine whether there is peculiar smell, such as the smell of burning, capacitor electrolyte, etc., for an experienced electronic maintenance personnel, is very sensitive to the smells: "touch" is by hand to test the temperature of the device is normal, for example, too hot, or too cold. Some power device, the work when the fever, if is cool to the touch, basically can determine it didn't work. But if not hot hot or the hot places where it's too hot, it is no good. General power transistor, voltage regulator chip, etc., work under 70 degrees is completely no problem. 70 degrees is about how a concept? If you will hand press, can do more than three seconds, it means that the temperature around 70 degrees (note first tentative to touch, don't handle scalded).
