Powcon 400SMT powers on, pops breaker when contactor switched from remote to "on"

admin

Just picked this thing up with a lot of other repairables.  With contactor set to "remote" and nothing hooked to plug it will power on and allow me to adjust amps no problem, but the second I switch it to "contactor on" it immediately pops the breaker regardless of amp setting.I'm going off of Schematic, non-fan on demand pages 34-35 here:https://arconweld.com/custom/Powcon_...SMT/400SMT.pdfI noticed two things - First that the lower blue capacitor in the center top of the unit (between main PCB and changeover mother board) shows some leakage and one of the wires looks like its gotten hot, but there isn't electrolyte everywhere, just on the edge of the capacitor.  I'm going to order some replacements shortly.Second is that if I disconnect J4-J5 from the main control PCB going to the "main SCR assembly" I can switch contactor to "on", the contactor light comes on and I hear a faint buzzing from the main PCB like its trying to trigger the SCR's.  If I disconnect J6-J7 for the opposing SCR on the main SCR assembly, breaker still pops.  Is this indicative that the main SCR assembly is shot, or that one of the SCR's within is latching and not letting go?  I've checked both J4-J5 and J6-J7 and their values are in line when on and both stay off when the contactor switch is turned to "remote" so I don't think its a problem with the main control PCB or the circuitry firing the SCR's.
Reply:Call the guys at Arcon where you got the schem. They have helped me over the phone on several occasions.Arcon Workhorse 300MSPowcon 400SMTPowcon SM400 x 2Powcon SM3001968 SA200 Redface1978 SA250 DieselMiller Super 32P FeederPre 1927 American 14" High Duty LatheK&T Milwaukee 2H Horizontal Mill

Bryan
Reply:Talked to guys at Arcon.  Going to order replacement capacitors and a main SCR.  I think that the J4-J5 SCR is the one which is working correctly, and the opposing SCR is the one which is stuck on.  They said that failing main SCR's is top cause of what I have happening, and that they still sell individual SCR's but no longer have any of the "main SCR assembly" that consists of a pair of SCR's sandwiched between heatsinks.