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Old Miller Big 40

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  • Old Miller Big 40

    About a month ago my mother in law gave me a miller big 40 welder. It had been sitting for 7 years. I cleaned carb, and fuel tank, and the engine fired right up. Since then I have not had much luck. I can not get the serial number to look up manual, but I think its a early 70s model. Its got a continental gas motor, and from the little bit of research I did it looks early 70s. The choke and the on/ off toggle switch are located in the back by the battery. I think thats a sign its early 70s model.
    the first thing i did was test voltage at 120vac, and I checked for DC across welding outputs. I have about 3VAC at plug, and about 3VDC at welding outputs. I bought a setting stone from welding supply store and cleaned slip rings and brushes. I also cleaned connections on brushes and the 2 rectifiers located just behind brushes. I have also found a wire that runs from the rectifiers to a resistor. The resistor has a hose clamp type thing wrapped around it with a wire hanging off it not tied to anything. There is also a wire hanging off the opposite end that it does not tie to anything. It looks like they are supposed to connect to the fine adjust, but im not sure. Also the fine adjust has no wires going to it. Can someone please help. Thanks in advance
    Last edited by THall3158; 11-01-2017, 02:48 PM. Reason: Last couple sentences did not get posted in original.

  • #2
    had to edit post for some reason the last couple sentences did not post in original.

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    • #3
      Welcome to the group !
      if you get the serial # on the faceplate and plug it in to the site you can download your manual

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      • #4
        D Auger,
        Im not able to read serial# bacause the face plate is faded out.

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        • #5
          Can you get and share some pics?

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          • #6
            Yes I can post some pics of it tomorrow...all the pics I looked at on the internet look like the choke and start stop were on the back(im assuming it's the back) its the opposite end of the generator.Sometime around mid 70s I think they moved choke and start stop to front side where wekding controls are.

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            • #7
              Engine serial # might get you in the ball park if it hasn't been replaced ,low hours ?

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              • #8
                You absolutely need the wiring diagram. That corn cob resistor is part of the weld or flash circuit and your rheostat is definitely part of that circuit. If you post a picture of the front I can get you in the ball park. But the older machines had the serial # stamped into the name plate. It should never wear way.

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