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jjohn76
Senior Member
Last Activity: Yesterday, 06:58 PM
Joined: 08-13-2018
Location: Los Alamos, New Mexico
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  • Puddles, I'd add that 800uF seems like a lot of capacitance to have for PFC in that welder. That makes for ~75A reactive current at idle. The 600uF (4x150uF) would be closer to the ~50A reactive current at idle I have seen in other 300-350 class machines. I have run 300 class machines on a 30A breaker...
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  • Hi Puddles, hopefully you received my PM. I wouldn't have any issue testing with the PFC capacitors (or just the one) pulled from the machine, but would advise discussing with the Miller Tech Support if you're concerned.

    A failed cap would likely show a short to the primary and pop your...
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  • Is this a different problem than the first post? What's your current breaker for the welder circuit? You will definitely need run caps instead of start caps if you want to keep the PFC option. Just remember, the PFC caps are an option. They are in parallel with the primary of the transformer to balance...
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  • jjohn76
    replied to XMT350MPA Repair Questions
    What test points are showing .20V?
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  • My bad, it was the MM 255......
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  • jjohn76
    replied to XMT350MPA Repair Questions
    My last post was marked for spam, hopefully this doesn't become a repost:
    not sure about the tests on U1 (if that's the same one with the low .20V spec) just yet. There are several other components in parallel with those pull down resistors that could have failed/shorted and caused a low reading....
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  • Ha! Have you seen the demo video Baker gas did for the MM252, or whatever the new inverter unit is? They used the auto configure (or whatever it is called) for material, thickness, and wire, and that beast sparked and spattered like crazy. Hopefully they figured it out......
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  • I just found somewhere that the MM141 has smooth start technology, which probably means it has a slower run-in speed like you're seeing.
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  • My old Millermatic 211 used to do that, and am pretty sure it's the run in set at the factory. Don't worry about opening it up yet. If you have gas or are running flux core, just try it. If you don't have the operator manual, download it from the Millerwelds.com->Support->Manuals and type in...
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  • jjohn76
    replied to XMT350MPA Repair Questions
    U1 gives me that low reading on both drivers. I have a couple other spare boards that don't show the low reading, but had to put the project down for a while before investigating further. The pulldown resistors for those drivers (R88 and R93) are connected through a number of resistors, and whatever...
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  • jjohn76
    replied to XMT350MPA Repair Questions
    I just pulled up my notes and a spare PC1. Just from D41 (PC1) and C15 (PC2) issues, it sounds like you had an overvoltage on the 15V auxiliary power supply. Given that the +15V powers nearly every component on the back half of PC1, you may find once you remove D41 and measure across it's terminals,...
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  • jjohn76
    replied to XMT350MPA Repair Questions
    Sounds good and that makes sense, there are two circuits right above PM1, the SCR driver (bigger resistors and relay are the giveaway on that) which gets a signal from PC1 to close that relay, which turns on each SCR at the right timing for its phase. The other circuit is the boost gate drive circuit,...
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  • jjohn76
    replied to XMT350MPA Repair Questions
    This is a pretty complicated welder as a first effort. It has more lethal voltage locations than others, and being industrial goes up big when it fails (lots of energy is stored in capacitors and those heavy duty transistors in normal operation, and much more when they're failing). I only use LEGIT...
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  • jjohn76
    replied to XMT350MPA Repair Questions
    Isn't that the input/side board? I don't see why the MPA would be different for that board, particularly in that area, as that PM1 just contains the power components that rectify and boost the input voltage to 960V DC (or somewhere thereabouts). If I am looking at the right place, that looks to be the...
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  • jjohn76
    replied to XMT350MPA Repair Questions
    ​​​​​​Are you planning to go through the main board as well? Have you gone completely through the pre-power checks?

    Are those resistors part of the pre-charge bypass circuit?

    Replacing the diodes is usually required when the IGBTs in those power mods fail....
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  • jjohn76
    replied to Wiring a spoolgun to xmt300
    If you're looking to build your own, you can get an idea from the old Spoolmatic 200 machines (might be off on the machine name) that had the built-in spoolgun control. By the time you get around to starting that project, you'll probably find a control box. That's been my experience at least.
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  • jjohn76
    replied to Spectrum 187 Plasma Cutter
    I can't remember which one is pm1, is that the input rectifier or output IGBT? What are you showing for input bus voltage on power up? Should be ~390VDC.
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