Ac electronic load power supply cannot DC output how to deal

When using ac electronic load power supply, there may be a lot of problems, such as: no DC output, how to deal with this problem?

500kw loadbank
500kw load bank
First we need to find out where the problem lies. If the AC electronic load power supply has no DC output, there may be several problems:
1.the fuse is burned,
2.The switch does not work.
3.control circuit failure.
If the fault is caused by these reasons, perform the following operations:
First, open the power supply box and remove the safety tube. According to the user's reflection, the insurance tube repeatedly burns. The lower rectifier diode and converter power switch tube are welded, all are normal when tested by multimeter, and no short circuit is detected at ac input end when tested by high resistance gear.
The user can judge according to the phenomenon that the fuse burns off, the fault place should be in front of the primary winding of the converter, but there is no short circuit. We had to go back to the original state, change the fuse and run the experiment. Switch on the AC power supply, the safety burns off, immediately disconnect the AC power supply inspection, the safety tube burns black. The AC input circuit is seriously short-circuited, and the AC input of the rectifier bridge is disconnected. The two ends of the rectifier bridge ac input are connected with a safety tube, directly connected to the AC power supply.
Switch on the power supply, the fan of the regulated power supply rotates normally, and the dc output voltage is normal. It can be seen that the fault is in the AC filter circuit, and the multimeter detection can not be done. At this time, I thought of substitution method, and removed two AC filter capacitors from another power supply to replace them. (Because welding is simple, the capacitor is changed first.) After power test, the DC regulated power supply works normally. The fault can be seen in the two capacitors, tested with high voltage insulation instrument, one of the