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, 01:03 PM #1Junior Member
- Join Date
- Sep 2013
Has anyone repaired PC1 on XMT 350 cccv?