Switching power supply how to repair
You ask too much, can not explain, there are many kinds of switching power supply, fault more, can not explain one by one, and I will only a little bit, generally burn the power to look at the insurance, if not off detection About the film, the visual resistance is not burning, the transformer is generally not bad, the resistance is also less common is the capacitor is broken or the insurance broke, and there are some lightning pressure varistor will burst, useless, just from To protect the role, get rid of it can.
Excluding the switching power supply after the above problems, indicating that most of the fault exists in the oscillation control circuit, sampling feedback circuit or load. At this time, we should first check the oscillation manifold power supply circuit is normal (test point four), the normal voltage should be about 10V (special reminder: because the test voltage should be in the case of power, and the power board has high pressure Electricity, so pay special attention to personal safety, can not try to directly touch the power of any part).
If the point of no voltage or voltage is very low, first of all to check the buck resistor is damaged; Second, then check the oscillation manifold and its external power supply circuit is normal. If the external circuit is not found fault, it is recommended to replace the oscillation manifold. Of course, sometimes the power supply can not be normal output voltage may also be due to load short circuit caused by power protection. For this power supply, we only need to remove the output line, check the output voltage is normal (test point five), you can determine the fault location. After the previous troubleshooting, and finally should also check the feedback circuit part, in general, this part of the main focus on the optocoupler and its amplifier circuit, to pay special attention.
First observe the power fuse is damaged. If the fuse is damaged, can not rush to replace, you must first check whether there is a short circuit power phenomenon. Method: With the multimeter of the electrical resistance test after the end of the power fuse (test point one), the normal resistance should be more than tens of kilo ohms, such as resistance is zero, then there is AC short circuit phenomenon. In addition, we should also focus on checking the power of the AC filter capacitor is damaged; the same time if there is a varistor, it should also check the resistance.
As the above test results are normal, we should then detect the power supply of the four rectifier diodes (test point two). In the normal state, the diode forward resistance of the number of k (with a multimeter × 1k block test), reverse resistance close to infinity. If you find that the test results are not normal, you need to replace. Along the investigation down, and then to do is test the DC resistance of this part of the power (test point three), the normal resistance is also a few k, such as the resistance is zero, then there is a DC short circuit. DC caused by the reasons for more short circuit, such as filter capacitor short circuit damage, power oscillation tube damage, oscillation manifold and the external circuit part of the damage may cause short circuit phenomenon. In this case, it should be noted that before replacing the power oscillation tube, you must determine the oscillation manifold and the external circuit is normal, otherwise it will cause damage to the power supply again.
