HVDC Ionization chamber

[Electronaut]

First year industrial electrician, but i have 3 years of commercial and resi. Also my first post here. 120vAC 3A input: 40kvDC 5mA output

So i work at a major canning factory and we coat sheets of metal with wax to protect food inside the cans. We send sheets of steel through a chamber with with electrodes on the top and bottom and what i think is a thicker S shaped bar that i assume is the return path for the DC under the sheet but in between the bottom electrodes which are just thing solid wires. We were having over heating issues a couple months ago and the chamber caught fire. we had it rebuilt and i soldered a new 7 pin connector on the power supply and got new high voltage electrodes. We also replaced one of the Variacs for the chamber current settings, and we replaced the temperature controller. it worked decently on and off but would have overheating issues sporadically. Now yesterday the Power supply got so hot that the big metal container that its in, which is filled with oil swelled up and it eventually popped the main 120V 30A breaker. The electrodes melted in the slots on the power supply and the insides of it were melted also and it smells awful. We also replaced the 480:120 step down transformer for the 120v circuit thinking it was failing and not sending enough voltage to the power supply which made it work extra hard to produce the same power the variacs are demanding. We do not have oscilliscopes or any fancy high voltage testing equipment but my boss still thinks we should be able to figure it out. I have schematics and everything. I guess im just looking for a direction to go on troubleshooting or finding out what part of the power supply failed so that maybe i can find the problem upstream or in the PS itself..

Thanks in advance