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Millermatic 350P display flickering then machine completely stops

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  • Millermatic 350P display flickering then machine completely stops

    I bought a used Millermatic 350P in 2011 which has been working fine until this last week. Before I purchased it, I called Miller and was told that the circuit boards had not been replaced in it.

    Millermatic 350P
    Year Mfg: 2007/Jan.
    LH010001 Style: LH01
    Model: Millermatic 350P
    Stock No.: 907379
    Serial No.: LH480282B
    Stock No. 907379
    Serial No.: LH490232B

    This past week it has started to fail intermittently.

    When it works without issue, I turn it on, it makes a small hum, displays "MM" and "350P," then displays the voltage/wire speed setting last used. I just went out and turned it on, and it did this just fine.

    Earlier this week, I got a "HELP 3" trouble code. Since the Bernard Q300 mig gun trigger lock was cracked and would sometimes get stuck depressed, I replaced the trigger with a new non-lock trigger and the "HELP 3" code went away.

    Yesterday, I was using the machine outside in 90F heat and various times when I would turn the machine on it would intermittently variously:

    a. Start with a large "hum," display "MM" and "350P" then the display would flicker, then go dark and the hum would be barely audible. If I pull the trigger there is no gas and no wire feed.

    b. Not start at all.

    c. Not start with a large "hum," but display the "MM" and "350P" then not display voltage or wire feed but go dark and any hum is barely audible. If I pull the trigger, there is no gas and no wire feed.

    d. Not start with a large "hum," but display the "MM" and "350P" and then show 21.5 volts and 400 wire speed (when my last use was 21.5/280) and then I would dial back to my intended 20.5/280 and it might run for a few welds, then go completely dark with no gas, no wire feed when I pulled the trigger.

    e. One time yesterday the "HELP 3" trouble code came back.

    f. Or after all of the foregoing, it would start and work perfectly for multiple welds until I turned it off.

    My machine is set up for 240volts single phase input, but I live in a rural area and I wonder if my power is suspect.

    I recently moved the machine in the back of a trailer 100 miles to its current location.

    I took the cover off the machine when I bought it in 2011 to read the serial number from the board to the MIller technician and the boards seemed clean, I can unplug it and do it again and look for screws which have vibrated loose, etc.

    Any help would be appreciated.
    Last edited by E350; 06-12-2016, 03:00 PM.

  • #2
    After couple years of using mine it did something similar but can't remember which help code but wouldn't weld. Was interment and would work if I restarted it. <br />
    Called LWS, he said pull covers and blow out completely with air. Very fine metal dust can cause these type issues. (I use plasma a lot in shop). Removed covers blew out, worked like new. Now I try & do once a year or so. Been running flawless since. <br />
    Hope it helps. Greg


    • #3
      Thanks Greg. Will do and will report back.


      • #4
        Reporting back: Took all the covers off the machine. Spent probably 20 minutes blowing it out with my air compressor, trying to get the nozzle near, but not touching in all the crooks and crevices. Today I started it up in Pulse Mode (I don't know how to use pulse mode) and ran a couple of beads. Then changed it back to short circuit mig at 19.0v and 180wf and welded some 14 gauge steel on a trailer.

        Machine performed perfectly. No problems.

        So thanks Greg!

        Fingers crossed that it continues to work without issues.