1. When the current regulator circuit fails, especially when the current transformer is damaged or the wiring is open, there is no current feedback suppression at startup, and the DC voltage will directly impact (Q angle 20 degrees), and the DC current will directly impact the value, causing overcurrent protection or main circuit switch tripping. Check whether the current transformer is damaged, whether the wiring from the current transformer to the circuit board is broken, and whether there are any components damaged or open circuit in the current regulator.

2. The power adjustment knob of the medium frequency furnace is in the position. Except for the quenching load, other loads require the power adjustment knob to be placed in the small position when starting. If it is not in the small position, the overcurrent protection or main circuit switch protection will trip due to excessive current impact. Check whether the DC voltmeter can reach about 500 volts. If it does not reach, it means that the rectifier silicon KP tube is broken.

3. Pull out the inverter line, that is, stop the inverter. There are six groups of rectifier control output lines on the mainboard. Pull out each group to see if there is any change on the voltage meter. If there is no change, it means that the corresponding thyristor is broken. If there is a change (the voltage will definitely become lower), it means that this group is good. Put it back and pull out another group. Check all six groups according to the law. If the thyristor is open-circuited, it is mostly because of insufficient voltage. A short circuit will burn the fuse or trip.