(1) Fuse blown
Generally, if the fuse is blown, it indicates that there is a problem with the internal circuit of the power supply.
1. Short circuit: A short circuit fault occurs on the line side, causing the fuse to quickly break;
2. Overload: If the load current exceeds the rated current of the fuse, the fuse will overheat and blow for a long time (usually 1.1 times the rated current for about 1 hour)
3. Pulse: When the circuit is started or the power supply is unstable, an instantaneous high current causes the fuse to open;
In addition, not tightening the screws or damaging the fuse during installation can also cause the fuse to blow. There is a difference between current short circuit and current overload: a current short circuit is a direct connection between the live wire and the zero wire, without passing through an electrical appliance, quickly generating an almost unobstructed current circuit. An extremely large current passes through a fuse, causing the resistance of the fuse to suddenly increase and generating heat energy that is instantly blown;
Current overload refers to the use of electrical appliances with excessive total power, i.e. excessive current consumption. When increasing the number of open electrical appliances, the current passing through the fuse continuously increases, and the resistance of the fuse gradually increases, resulting in thermal energy being blown.

(2) No DC voltage output or unstable voltage output
If the fuse is intact, there is no output of DC voltage at all levels under load. This situation is mainly caused by the following reasons: open circuit and short circuit phenomena in the power supply, faults in overvoltage and overcurrent protection circuits, auxiliary power supply faults, oscillation circuit not working, excessive power load, breakdown of rectifier diodes in high-frequency rectification and filtering circuits, leakage of filtering capacitors, etc.
If the fuse is intact, there is no output of DC voltage at all levels under load. This situation is mainly caused by the following reasons: open circuit and short circuit phenomena in the power supply, faults in overvoltage and overcurrent protection circuits, auxiliary power supply faults, oscillation circuit not working, excessive power load, breakdown of rectifier diodes in high-frequency rectification and filtering circuits, leakage of filtering capacitors, etc. After measuring the secondary components with a multimeter and ruling out high-frequency rectifier diode breakdown and load short circuit, if the output is zero at this time, it can be confirmed that the control circuit of the power supply has malfunctioned. If there is a partial voltage output, it indicates that the front-end circuit is working normally, and the fault is in the high-frequency rectification and filtering circuit. The high-frequency filtering circuit mainly consists of a rectifier diode and a low-voltage filtering capacitor to form a DC voltage output. The breakdown of the rectifier diode will cause the circuit to have no voltage output, and the leakage of the filtering capacitor will cause faults such as unstable output voltage. Using a multimeter to statically measure the corresponding components can detect the damaged components.