If a switching power supply is faulty, 90% of faults can be located by following the four steps of "Inspect - Test - Disconnect - Replace":

1. Inspect

After powering off for 5 minutes, visually inspect the housing for bulging, burning, blown fuses, or capacitor leakage, taking photos for record.

2. Test

Use a multimeter in the DC range to measure the main capacitor: 300 V ±10% at no load. Below 250 V indicates a defective rectifier bridge or filter.

Measure the output: No load should be ±5% of the nominal value; short circuit should be 0 V, the fuse is intact, and the secondary rectifier is broken.

3. Disconnect

Unplug the load and use a 30 W/12 V automotive light bulb as a dummy load:

If the light bulb lights normally, the power supply is OK, and the problem lies with the load.

If it does not light or flickers, proceed to the next step.

4. Replacement

Prioritize replacement of vulnerable parts: large electrolytic capacitors (capacity drop > 20%), rectifier bridge, power transistors, optocouplers, and PWM chips.

Before powering on, connect a 60W bulb in series with the 220V input to limit the current. If the bulb doesn't light, operate at full voltage.

Complete initial screening in 3 minutes, then replace and retest in 10 minutes, quickly restoring power.