Sub-controller power switch, separate the main switch of the device, wait for 20 minutes, the safest, generally the capacitor has a discharge resistor inside → change the same voltage level and capacity capacitor; the main switch has electricity to have a personal monitoring → if the capacity change Large, that branch switch and a large line have to change large → after the capacitor is replaced, the screw is detected, and the insulation and the short circuit are detected by the shaker and the multimeter.