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Miller 320A/BP - Not Working, Really confused

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  • Miller 320A/BP - Not Working, Really confused

    Serial # 72-624599 using the circuit diagram from the 1973 users manual

    Ok, got this beast home and finally got it hooked up, made a single SHORT pass (GTAW Straight polarity) something "clicked" in the machine, and now, no nothing from the machine. The fan won't even come on. The feed for the water cooled torch is rigged onto the machine a little goofy, there's a block similar to a lug you would use to connect a tig torch to a stick machine, and I think it may have shorted to the welders frame during the pass.

    Here's what my basic troubleshooting has got me so far:

    Voltage at the breaker - 240V across the two power wires and 120 from power to ground
    Six foot of #4 wire from the breaker to the machine
    Voltage at the input lugs - 39V from one lug to ground, 120 from the other to ground and 68V Lug to Lug
    Fuses - the 3 fuses I could find Large at the back, two 10amps at the front all check out
    At the large contactor on the left side, I'm getting 68 Volts across the lugs.

    No change resetting the breaker on the front (seems like its very "loose" for a breaker)

    WTF is going on? Am I missing a fuse somewhere in the diagram? Or did I jsut short the main transformer completely out?

  • #2
    That's weird. Are you saying you have 240 v across the two legs of the line at the breaker, and only 68 v between the two legs at the other end of the wire where it attaches to the welder? Hoping I'm missing something here--that just doesn't make any sense at all, which is probably why you sound frustrated. If that's right, you have a break in your input feed wire and you need to replace it.


    • #3
      Is it possible I "fried" Capacitor C1? and that shorting to ground or to line 2 is causing the low voltage?


      • #4
        Yes, thats what's wierd.
        Using the designations, White, Black and Green:

        White to Green - 120V
        Black to Green - 38V
        White to Black - 68V

        This is at the Lugs on the back of the machine (hooked up to it?)


        • #5
          if you have a short that is pulling the voltage down that much, it seems the breaker should be tripping. At the very least, the wire should getting hot. Yes, a shorted capacitor can pull the voltage down, but not without some serious current draw. Do you by any chance have a clamp-on ammeter?


          • #6
            Is the machine connected with a plug and receptacle, or wired directly to the breaker?


            • #7
              Directly to the breaker


              • #8
                Sorry, and yes to the clamp on meter. Maxes at 20 amps though.


                • #9
                  Ok, round three...

                  Machine OFF :
                  Green to White - 120V
                  Green to Black - 120V
                  White to Black - 0V

                  Machine ON:
                  Green to White - 120V
                  Green to Black - 38V
                  White to Black - 68V

                  No Amps recorded on White Wire machine on or off, couldnt get it around Green or Black

                  Breaker is a 60 Amp 2 phase 240V breaker


                  • #10
                    First, is the welder on or off when you see these crazy voltages? If on, do they become normal when you turn it off? Are any of the feed wires getting hot?

                    The only schematic I could find on line is for a much newer machine. However, it should be close enough. C1 is just for power factor correction, so just disconnect one side of it and see what happens. Fact is, unless you have the output contactor W on, by putting the remote contactor switch on or hitting the pedal, C1 isn't even in the circuit. Anyway, tThe machine will work fine without it, and contrary to popular belief, it will NOT raise your electric bill to take it out unless you have an industrial meter installation that can measure apparent power. The typical home/shop meter measures real power, not apparent power, so it won't affect your bill. May irritate the power company a bit if you're using this machine industrially but otherwise, don't worry about it.

                    Put the clamp on meter around the white wire and see what current you have. Should be zero with the power off, and not much more with it on inless you close the output contactor and weld. Turn the welder on and see what you get. Also check the green wire. There had better be zero current there or there is a bigger problem.

                    Can you scan the schematic diagram from your manual and post it? Here's the one I'm using.
                    I'm off to bed--us old guys need their sleep. :-) Will check with you in the morning.

                    Click image for larger version  Name:	oldest schematic.jpg Views:	0 Size:	163.1 KB ID:	608306


                    • #11
                      Ok, Thanks Aeronca... Thank goodness it wasn't that complicated, just a dumb operator.

                      If at first you don't succeed... G back to first principals. What did YOU CHANGE?

                      New installation - new breaker, new wire,etc.

                      Good voltage at breaker, but crap at the other end...Start at the beginning.

                      Pulled the breaker with the wires attached, and tried to give them a "snug up" just to be sure. And the Mother#$%^)( black wire falls out from UNDER the lug, not in it...Which allows you to get the lug Tight, but not make virtually ANY contact. TADA no 2 phase and crazy voltages.

                      FYI - Welder works fine. Sorry just been a long day with little sleep.

                      Thanks again.


                      • #12
                        Fantastic! Had to be something like that. Glad it was such an easy fix. As I am fond of saying, the only people that never make a mistake are those that don’t do anything!