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Miller XMT 304 Help1 Code On 'electrode hot' settings only

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  • Miller XMT 304 Help1 Code On 'electrode hot' settings only

    Hello all. I'm hoping someone might have some advice for me. I recently purchased a miller XMT 304 and I keep getting the Help 1 code, but only on the 'electrode hot' settings. If I put the welder on MIG, it starts up fine. I can adjust everything and the display changes accordingly. I dont have a MIG gun or anything so I haven't been able to try to weld with it on the MIG setting. As soon as I switch it to any of the electrode hot settings (I want to be able to use it as a stick welder for now) it throws the code. I have searched this forum many times and it seemed like the PC1 board is the likely culprit. I sent my PC1 board away to get repaired. Received the newly repaired board back, no change. I have checked my input voltage, I am sitting around 256V on a 50A outlet. Also checked my plug and power switch wiring and it appears correct according to the owners manual. I borrowed an older welder (Miller Thunderbolt) to get some work done and it worked just fine on my power outlet.

    If anyone has any ideas or has experienced this issue before, any help would be greatly appreciated!

    Thanks in Advance

  • #2
    If you're planning on fixing it yourself, first step is to download a service manual (google) and follow the pre-power inspection procedure. Help1 is often a problem with the big capacitors, the input contactor, bleeder resistors, or something else on the power board on the side of the unit. Pay particular attention to the physical condition of the capacitors - if they have any bulges, lumps, ripples, or other visible oddities, they need to be replaced.

    Hopefully you weren't told that this was a working unit when you bought it...


    • #3
      Ok sounds good. I will try to get that tested tomorrow if I can. Thanks very much for the reply. And no, I am not surprised that it doesn't work. I picked it up for $800 at an auction, so I figure its worth it to throw a few bucks at it if I have too. I downloaded the service manual for the Red D Arc EX300. Seems like they are the same machine.


      • #4
        It sounds like you have the 230/460 VAC type of unit, but verify that. Also, can you tell me if the contactor pulls in about 1-2 seconds after turning on the power switch?

        Most common causes:
        - Contactor never pulled in (W1 when on 230v, W2 when on 460v)
        - Shorted tank Capacitor (C1) this should measure .34 uF when you isolate it and measure it with a meter
        - Open CT1 (Usually plugs into RC6-1 and 6-2 and should measure almost 0 ohms)

        If the contactor did not pull in, you need measure the coil resistance of each coil (W1 and W2). Each should measure about 7 - 8 ohms.


        • #5
          I had a contactor that was clicking but not pulling in. The interlock mechanism was jamming and only allowing the plunger to move halfway. It sounded like it was doing things, but the contacts never closed. I've also seen pictures of burnt contactor contacts in one, with a similar symptom. My test was to use an external power source to run the coil with the unit off (and original coil wires unplugged) and measure to see if the contacts actually closed. I used an 18v battery from my cordless tools.

          Measuring the capacitor voltages would be a good starting point if the pre-power checklist doesn't find any problems.

          If the contactor doesn't pull in, and you're using 240V power, you'll also find the +/-15V rails are low, which is another good indicator.