To avoid the $600 + cost of a replacement and just because I accepted the challenge on a Miller XMT 350 repair. I decided to test and repair the board that failed, PC1, well to an extent. (PCB part# 242-812) Before I go on, thank you but please hold all comments about the dangers of this machine. I am aware of the theory miller came up with on this newer design (great idea btw), I can respect how it works, and I am not an amateur at this, this is what I do. I was just looking for a place to bounce ideas off of capable people. That being said; the issue was that the power circuit on PC1 that drives the control power transformer had failed. I traced the failure to U1, U6, Aux power IGBT and protection diode. (finding the replacement IGBT was a challenge in itself. Semikron SK10GHR123) Verified all power off test ok, power up and all seemed ok, then the entire unit would cycle on and off. I noted power to U6 (PWM driver) @ 3.6 v after the unit would not turn back on. I am repairing this blind, I have no prints, I was wondering if someone knew what regulates logic power to this circuit. It appears to operate on a zenor regulator off of rect_+, but not quite. Any thoughts would be appreciated. I walked away from it for the weekend, but suspect a power issue or U6 is soft cycling for some reason, such as over current from china replacement part. Mike
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09-01-2013, 02:03 PM #1Junior Member
- Join Date
- Sep 2013
Has anyone repaired PC1 on XMT 350 cccv?
09-03-2013, 11:16 AM #2
PC1 is a very rare on these units to up and blow, what was the error code? Repairing a board without the circuit diagram is somewhat stupid and rather dangerous.
What is the serial# of the machine? If its a MAxxxx+, its likely that Miller will cover the repair, parts wise, ie, parts only, labour not included
Last edited by cruizer; 09-03-2013 at 11:25 AM.
09-03-2013, 08:36 PM #3Junior Member
- Join Date
- Sep 2013
I've seen your responses to other posts and figured I'd get one similar. Thanks for the brilliant insight. miller no long gives the prints for the newer boards. The power circuit failed so there for there is no power up to give a code. I know PC1 is rare to go, like I said, this is not my first go around, I'm reaching out to other minds . thanks for your input. BTW not MA #, out of warranty, already went that route w miller. just trying to help a customer out, we repair many boards when possible.
09-04-2013, 12:59 PM #4
So its a mid year LK serial#. as that is the one that comes up for that board, really better off getting a replacement. Alot of those chips / linears are programmed, and the boards appear to be layered, making em pretty tough to fix. Personally I wouldn't bother. I too fix many boards, but these I don't bother with due to the cascade problems with them. Miller never gave the prints to the newer machines, because of copyrights, and becase they changed quite a bit from manufacturer to manufacturer.