Introduction of maintenance skills of switching power supply
1. When overhauling the switching power supply, check the circuit with relatively high failure rate first.
When overhauling the switching power supply, if it is judged that there may be problems in two or more parts at the same time, the parts with higher failure rate should be checked first. For example, for the switching power supply, there is only a voltage fault at the moment of starting, and the fault may be caused by overvoltage protection caused by the high output voltage due to the problem of the voltage stabilizing circuit, or by a short circuit or overcurrent fault at an output terminal of the switching power supply. However, the possibility of the latter is far greater than that of the former, so when overhauling, it is necessary to check whether the voltage output terminal of the switching power supply has short circuit and overcurrent faults. Then check the voltage stabilizing circuit according to overvoltage protection.
2. When repairing the switching power supply, the wearing parts should be inspected first.
From the structure of switching power supply, each switching power supply has its own advantages and disadvantages, and there are also relatively fixed wearing parts. In terms of the service time of electronic equipment, the wearing parts of the switching power supply also have certain rules. For example, when the switching power supply is used for a long time, the electrolytic capacitor fault at the hot end of the switching power supply is relatively high. When overhauling the switching power supply, we should focus on checking these vulnerable parts before overhauling according to the conventional method, which can get twice the result with half the effort.
3. When repairing switching power supply, be good at using observation method.
(1) observe whether the fuse in the insurance is blown, and judge whether there is any serious short circuit fault in the switching power supply.
The direct cause of fuse blowing in AC 220V rectifier and filter circuit is only in several components fixed at the hot end of switching power supply, namely, switching tube, 300V large filter capacitor, AC 220V rectifier diode breakdown and so on. Therefore, if it is observed that the fuse in the insurance is blown, it must be a problem with one of the above components.
(2) Observe whether the top of the electrolytic capacitor in the switching power supply swells, and judge whether there is a problem with this capacitor.
If the capacitor swells, it means that the capacitor is basically invalid and needs to be replaced. At the same time, it is necessary to check whether the reason for the capacitance swelling is natural damage after working for a long time or damage due to excessive voltage, so as to prescribe the right medicine.
4. When repairing the switching power supply, learn the skills of voltage method.
Using voltage method to overhaul the switching power supply can determine whether the fault is in the switching power supply and where it is. The common key points of voltage overhaul of switching power supply are: AC input end of switching power supply, output end of rectification filter, drain and grid of switching tube, start end of switching power supply control chip, output end of switching power supply, etc. The fault point can be found by comparing the measured value with the normal value.
5. When repairing the switching power supply, you should learn the skills of using resistance method.
Resistance method can judge whether there is breakdown short circuit and serious leakage fault at each voltage output end of switching power supply, and confirm whether a component in switching power supply has breakdown, open circuit and leakage. The resistance method is most commonly used to check the open circuit of the safety resistor in the switching tube and AC 220V rectifier filter.
