I have the FC350BJ motor controller on my Cummins mini-mill.? It is also used on mini-lathes so this applicable to this forum.? It's a second hand machine so I don't know its history.? ?Motor/controller was running as new.? Machine was unplugged and not used for a few weeks.? Plugged her back in and the motor would not turn-on.? The switch portion of the potentiometer/ switch was faulty.? In the CCW position the switch should be closed.? I had ~1 Meg Ohm of resistance.? The transformer for the low voltage +15V, -15V? circuit was open on the primary side.? Luckily LMS eventually had these parts in stock. LMS Part# 2492(Transformer), #1282 (Potentiometer).? ?I am grateful for their sourcing of replacement parts.? After replacing the two known faulty components, the mill now turns-on with full range speed control.? I have not yet tested under motor load.
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I understand that the potentiometer will eventually wear out. The fact that LMS carries the transformer leads me to believe that this is a somewhat common problem with this controller.? I did not find anything on the web about this particular problem.? Hence one reason why I am posting here.? Maybe help out another person that has experienced this fault.?
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Right now, my only brainstorm is there was a power surge when the pot/switch was in the CCW position.? The Metal Oxide Varistor didn't clamp and protect transformer, but it did clamp and drew more current than the pot/switch could handle. I have not yet replaced the MOV on the PCB.? ?I haven't completely thought through the problem, yet here I write.?
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Does anyone here have advice on other components that may be faulty/compromised that lead to burn-out of the switch and transformer?? Or modifications that can be done to make this controller more robust that are worth the time and money???
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Resources that I used to assist me during my debugging:
John Gerling's write-up
https://olduhfguy.com/
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For now, the mill is up and running.? I am still eyeing the KBMD-240D as a more robust alternative.
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Regards,
Gary
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