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Weird issue with my 1988 Miller Air Pak... No power when first started?

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  • Weird issue with my 1988 Miller Air Pak... No power when first started?

    I've got a weird issue with my 1988 Miller Air Pak (SN: JK657718). It has the Deutz F4L912 motor. The unit fires right up and runs great. But, it will not produce 240v power (tapped straight from the junction box) and I can't strike an arc at first. If I let the unit run a while (sometimes 2 minutes, sometimes 45 minutes) it will start producing power and run fine. I have cleaned up the contacts for S1 and S2, and have checked all fuses (including the one under the upper panel). All appear to be good. It doesn't matter what position any of the switches are in, either. Once it does start producing power, it welds perfect and is capable of powering my entire house through the 240v outlet I installed off the junction box (per the manual). Once it produces power, all amperage ranges as well as all settings of the fine amperage adjustment work perfectly. Another weird thing I've noticed, is that the 110v outlets do have power even when the 240v receptacle and stinger don't have power. After about 10-15 minutes of running, the machine idles down perfectly and seems to kick up speed as soon as a load is applied to the 110v outlet. It seems as if this issue is separate from the speed control system, but I don't really understand the circuits I'm dealing with. I know that the machine had been sitting for several years before I purchased it, but it confuses me as the problem comes and goes. The unit has ~2500 hours on it. Also, once I shut the unit back down it seems hit or miss as to whether I will have power when I restart, or if I will be playing the waiting game for the unit to start producing power.

    Any ideas on what might be going on? I posted a thread at the MillerWelder forum, but I'm waiting on them to approve it. Figured I might give the pros here a shot!

    Any and all advice is greatly appreciated. I'm fairly capable, and have plenty of tools at hand to do whatever is necessary to fix it. I've done extensive mechanical and electronic repair of all makes/models of vehicles (cars, trucks, motorcycles, and heavy equipment). I've read online that some people will flash the field windings from another 110v outlet to each of the poles of the 240v outlet to make it start producing power. Does that sound like a reasonable thing to do Seems kinda sketchy to me. But, if necessary, I can wire up a cord to do just that. I have plenty of multimeters, but nothing capable of testing capacitors.

    Any thoughts or advice?

    ~Will Courtier~

  • #2
    Clean the crap off your slip rings. I use brake cleaner and a strip of fine emory soaked in brake clean


    • #3
      I actually have an update for this. I originally tried posting this on Thursday but the moderators hadn't approved the post yet.

      I inspected all of the wiring behind the upper panel, as I've heard that these units have frequent connection problems which cause similar gremlins. I noticed that the unit would generate power one second, then stop the next. Then generate power, and stop again. It seemed that as I hinged the door down and up, it would make/break connection. Then, all of a sudden, a fire developed behind the PC1 board. I shut the unit down, and removed the board. The board appeared to have had a small break at one of the solder pots, which was causing a poor connection. I'm guessing that as I moved the wiring back and forth, it stretched thin enough to get pretty warm and lit the board varnish on fire.

      After that happened, I figured I'd try to figure out where the wire ran to. I traced it out as best I could, and it appeared to be a wire that ran down to the brushes. I seen no shorts in the wire, so I removed the brushes to check them out. The brushes were well over 3/4" long, but the slip rings were a little bit dirty. This all seemed consistent with the unit's hours, as it only has about 2700 hours of use on the clock. I broke out my brass brush and cleaned everything up. Luckily, the local Miller warehouse stocked the PC1 board, and I confided in the shop I ordered the part through (Arcet of Norfolk, VA). They agreed with my diagnosis and said the board should fix me up. They also stated that these units rattle themselves apart over time, and that generally wreaks havoc on the circuit boards. Taking into account some sort of a military discount, I'm looking at $275 for the board and a few days of waiting.

      So, I should have the machine back up and running by Wednesday. I'll keep everyone up to date on how this plays out. Thank you guys for your time!

      ~Will Courtier~


      • #4
        The board arrived, and I got it installed. The unit immediately started producing power and runs great. The job was a complete success! Now to finish up with the small modifications to the trailer and make her mine... I'm in the process of installing an air hose reel, modifying the bottle bracket to hold my bottle, installing some LED flood lights for working at night, replacing the trailer lights, and adding some other things to help me out (metal vice, more tool storage, and a rack for hauling metal stock). She's quickly taking shape! I also picked up a 200amp tig torch so I can start doing some welding on Stainless.

        Thank you to everyone that helped out. I think she's ready to make some money!

        ~Will Courtier~