Power failures account for the majority of electronic equipment failures in electrical troubleshooting. Therefore, being familiar with the common faults and maintenance skills of switching power supplies is conducive to shortening the maintenance time of electronic equipment failures and improving personal equipment maintenance skills.

1. Common faults

(1) Fuse blown:

In general, a blown fuse indicates a problem with the internal circuit of the power supply. Since the power supply works under the condition of high voltage and high current, the fluctuation and surge of the grid voltage will cause the current in the power supply to increase instantaneously and cause the fuse to blow. The key point should be to check the rectifier diodes, high-voltage filter electrolytic capacitors, inverter power switch tubes, etc. at the input end of the power supply, and check whether these components have breakdown, open circuit, damage, etc. If the fuse is indeed blown, you should first check the various components on the circuit board to see if the surface of these components is burnt and whether there is electrolyte overflow. . It is necessary to pay special attention: when a component is found to be damaged, it must not be turned on directly after replacement. It is very likely that the replaced component will be damaged because other high-voltage components are still faulty. Be sure to conduct a comprehensive inspection of all high-voltage components of the above circuit. After checking and measuring, the fault of blown fuse can be completely ruled out.

(2) No DC voltage output or unstable voltage output

If the fuse is in good condition, under the condition of load, there is no output of DC voltage at all levels. This situation is mainly caused by the following reasons: open circuit and short circuit in the power supply, overvoltage and overcurrent protection circuit failure, auxiliary power supply failure, oscillation circuit not working, power supply overload, rectifier diode in high frequency rectifier filter circuit Breakdown, leakage of filter capacitors, etc. After measuring the secondary components with a multimeter and ruling out the breakdown of the high-frequency rectifier diode and the short-circuit of the load, if the output is zero at this time, it is certain that the control circuit of the power supply is faulty. If there is some voltage output, it means that the pre-stage circuit is working normally, and the fault is in the high-frequency rectifier and filter circuit. The high-frequency filter circuit is mainly composed of a rectifier diode and a low-voltage filter capacitor to form a DC voltage output. The breakdown of the rectifier diode will cause no voltage output in the circuit, and the leakage of the filter capacitor will cause the output voltage to be unstable and other faults. The damaged components can be detected by statically measuring the corresponding components with a multimeter.

(3) Poor power load capacity

Poor load capacity of power supply is a common fault, which usually occurs in old-fashioned or long-working power supplies. Should focus on checking whether the Zener diode generates heat and leakage, the rectifier diode is damaged, the high-voltage filter capacitor is damaged, etc.