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Millermatic 130XP - rheostat and PC1 problems (maybe worse!)

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  • Millermatic 130XP - rheostat and PC1 problems (maybe worse!)

    This is a copy of a message I just sent to Miller Tech Support. I am posting it here just in case anyone else has experienced anything even remotely similar.
    I am a NOOB MIG welder, but learn new things quickly. I only hope what I learn from this experience, I can share with others. This post may seem long-winded, but I have tried to supply as much detail as possible about my welder problem. If I need to supply additional info, feel free to leave your questions and/or comments.

    I recently bought a used Millermatic 130XP for home use. The former owner gave me a decent deal due to problems with the wire feed.
    Being a handy guy, I figured I could fix it, (thinking it might be a flaky fuse).
    When I got it home, I fired it up and noticed the wire feed didn't run at all. I pulled the cover and checked the fuse, it was fine. I disconnected power, disconnected the gun, cable and stinger connector from the unit and removed the wire roll from the spool. I jumped the trigger connections to simulate a pulled trigger on the gun. I then set the power selector to "fan only" and plugged the unit in to the wall. When I turned the power switch on, the fan ran, but the wire feed motor didn't operate, even though the trigger connector was jumped.
    I switched off the power then changed the power selector to 4 and switched the power back on. I turned the wire feed to 100 and...NOTHING!
    I began tapping in the little black relay (PC1) on the circuit board...HEY, the big contactor clicked closed and the wire feed motor started turning!
    When I turned the wire feed rheostat downwards, CLICK, the contactor opened and the wire feed motor stopped running. I turned the unit off and unplugged it from the wall. I suspected a rheostat problem. I removed the wires from the rheostat, drawing a little diagram as to which of the 3 lugs the 2 wires were connected to, (and marked the wire connectors with a sharpie). I then removed the rheostat from the unit for visual inspection and resistance testing.
    After checking the 3 lugs with the multimeter, I determined there was a fault in the wire winds because connecting the 2 outer lugs gave me NO resistance or continuity. I found that by connecting to the middle lug (wiper) and the unused lug on the rheostat, I had an almost complete range of resistance from 0 to 16 ohms. When I connected to the wiper and the other "used" lug, I only got 16 ohms at the end of travel, but when I turned the wiper, the resistance immediately dropped to 0. Upon close visual inspection, I noticed there was a break in the wire winding right next to the end of the wiper travel. This explained why the motor only ran at 100% wire speed!
    Out of curiosity, I replaced the rheostat back into the unit and connected the wires to the middle wiper lug and the previously unused lug on the rheostat, figuring the rheostat would work, but in reverse.
    I plugged the power cord in and turned the unit back on, NOTHING...HMMM!
    I then tapped on the little black PC1 relay on the circuit board...CLICK...HEY...the contactor closed and the wire feed motor began running! I turned the rheostat knob back and forth to test my theory, and I was right! I had almost a full range of motor speed in all power ranges!
    Seems like I solved one problem, the rheostat is bad, but there's a second problem with the PC1 relay on the circuit board. It needs to be smacked around a bit with a screwdriver handle in order to send voltage to the contactor and wire feed motor circuit.
    My question to Tech Support, I suppose, is...DID I diagnose the problems correctly and completely, or, is there yet another problem, other than a bad relay on the circuit board that is causing me grief here?
    I figure since the wire feed motor runs well, through all speed ranges and power levels, (albeit with the speed selector being turned the opposite direction on the housing). All seems to work with a rap on the PC1 relay. The only thing is, if I turn off the power switch and turn it back on, NOTHING WORKS!
    That is...until I rap on the PC1 relay again.
    THIS WILL NOT DO! How do I fix my newly purchased welder? I know it's repairable, somehow!
    And you know what? I haven't even checked the arc yet! Or, for that matter, the gas solenoid!
    I have a feeling it will work just fine, I just need some good advice!
    Last edited by docdeath; 05-01-2012, 09:49 PM.

  • #2
    Anything that has to move to operate, such as a relay is your most likely culprit.

    If you look at the outside of the relay, it usually has a part #. Write it down and go to digikey or Newark.com. Order the relay in and install it. Get a good soldering iron, and some solder wick

    After you find the #'s and write them down, you can carefully pull the plastic tops off the relays and have a look at the points. Sometimes you can adjust them to work for the time being.

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    • #3
      Thanks for the quick response.
      I was wondering if it would be wiser to replace the entire circuit board because maybe a component on it supports the relay in some fashion, allowing it to trip like it should.
      I actually de-soldered the relay and removed the top and peeled the side walls down to have a look. I used a points file, (which is actually a very thin, flexible strip of abrasive steel), to clean the contacts. The contacts and the rest of the relay looked to be pristine, all nice and shiny. After reattaching the relay, it still worked the same. I still had to rap on it to get the welder to power up.
      I searched the web for the rheostat, I had very little luck finding an Ohmite 16 ohm, 25 watt wire wound rheostat. The part number on it is the same part number Miller shows in the manual. I hope Miller can help with that!
      I have the top from the relay enclosure, (not necessary for it to operate), which I will use to search for a replacement. I kinda think it's the board as a unit, not just the relay, though. I could be wrong.

      Comment


      • #4
        Hi
        Quick way to do the repair is to buy the board, the fun way is to fix the board. Mouser has the following Mouser Part #: 588-RJS16RE
        Manufacturer Part #:
        RJS16RE
        Manufacturer:
        Ohmite
        Description: Rheostats 50watt 16ohm 750V Std Shaft
        at about $40.00 . If you decide to repair the board get out your big magnifying glass and look for cracked traces on the board and/or cracks in the board also cold solder joints. The attachment points of connectors is a good place to start and around the base of the relay but depending on the mounting and the history of the board there could also be problems elsewhere. Watch out for static discharge from you onto the board as it can be enough to fry solid state devices.
        I guess it also depends on how quick you need the machine back in service and how adventurous you feel.
        Meltedmetal

        Comment


        • #5
          Originally posted by Meltedmetal View Post
          Hi
          Quick way to do the repair is to buy the board, the fun way is to fix the board. Mouser has the following Mouser Part #: 588-RJS16RE
          Manufacturer Part #:
          RJS16RE
          Manufacturer:
          Ohmite
          Description: Rheostats 50watt 16ohm 750V Std Shaft
          at about $40.00 . If you decide to repair the board get out your big magnifying glass and look for cracked traces on the board and/or cracks in the board also cold solder joints. The attachment points of connectors is a good place to start and around the base of the relay but depending on the mounting and the history of the board there could also be problems elsewhere. Watch out for static discharge from you onto the board as it can be enough to fry solid state devices.
          I guess it also depends on how quick you need the machine back in service and how adventurous you feel.
          Meltedmetal
          Great call on the rheostat!
          I didn't have any luck because I was looking online for a 25 watt, 16 ohm rheostat using the actual Ohmite part number on the rheostat from my unit.
          There's an electronic surplus store near me that has a huge inventory of used and obscure industrial and military hardware and electronic parts. I went there today and rooted through their stash of rheostats. The majority of the stuff was manufactured by Ohmite. Unfortunately most of it was rated at 75 watts and upwards. The bins marked 100 ohms and less was pretty empty, but the other 5 or 6 bins of higher rated rheostats were packed with stuff. I need to go back and check some more as stuff gets placed in the wrong bins and I need more time to root through the bins of higher-rated rheostats.
          Since the circuit board is easily removable and only has a single muti-pin straight connector on it, maybe I'll pull it and go over all the solder joints on it. It has about 20 or 30 components on it so it shouldn't take long to give it a once-over. If that doesn't cure it, maybe then I'll spring for a new board.
          The thing is, I want to be sure it's that board causing the problem.
          I'm relatively sure that's where the problem lies because the unit came to life when I rapped on the relay housing on that circuit board.
          Has anyone here ever had to replace this circuit board on a 130XP?
          I haven't heard anything from Miller Tech Support yet about this, does it normally take a while to get a response from them?
          I figure if anyone's an expert, it would be someone on their Tech Support crew!
          Additionally, I think Miller would want to jump in and sell me the parts I need and keep a new customer happy and welding!

          Comment


          • #6
            Hi again Doc,
            Sounds like you are comfortable with electronics so I won't bother with many warnings about the perils of overheating things on the board etc. I have also found that it is sometimes hard to get exact replacements for electronic parts but as I'm sure you know as long as you replace with a more robust part that covers the pertinent specs and you have the physical room to install it you're good to go. The electronics industry is moving so fast that parts are sometimes obsolete before the equipment hits the showroom and it can be hard to find a suitable replacement. You are very fortunate to have a surplus store near you. Closest one to me is about 75 miles-the price of country living. The other thing about surplus is if it's not there today it might be next week. There may well be cheaper sources than Mouser online, I didn't look that hard, but they do have a broad inventory and for convenience don't overlook Radio Shack although they are not as good as they used to be for parts. Good luck with your project.
            Meltedmetal

            Comment


            • #7
              Originally posted by Meltedmetal View Post
              Hi again Doc,
              Sounds like you are comfortable with electronics so I won't bother with many warnings about the perils of overheating things on the board etc. I have also found that it is sometimes hard to get exact replacements for electronic parts but as I'm sure you know as long as you replace with a more robust part that covers the pertinent specs and you have the physical room to install it you're good to go. The electronics industry is moving so fast that parts are sometimes obsolete before the equipment hits the showroom and it can be hard to find a suitable replacement. You are very fortunate to have a surplus store near you. Closest one to me is about 75 miles-the price of country living. The other thing about surplus is if it's not there today it might be next week. There may well be cheaper sources than Mouser online, I didn't look that hard, but they do have a broad inventory and for convenience don't overlook Radio Shack although they are not as good as they used to be for parts. Good luck with your project.
              Meltedmetal
              Thanks, Meltedmetal!
              Today, I called the local Miller distributor - Praxair Corp. to find out about replacement parts. After a brief conversation, the guy gave me a number for their local parts guy.
              I called them and spoke with a helpful tech who told me I did a great job troubleshooting my unit. He told me most folks he deals with have no idea what is wrong with their welders, but, they just want it to work, which makes a good day for the sales dept. He then gave me some astoundingly high prices for replacement parts. The upside is, he also offered to fax or email me a copy of the schematic for the PC1 printed circuit board so I could do some further testing. At least that way, I had a small chance of tracking down a bad component on the circuit board. As I already know the rheostat is trashed, my next project is to try and attempt a fix on the circuit board, to try and save the expense of a new PC1 board.
              I also made another trip to the local electronic surplus store today. I spent about an hour rooting through numerous bins, searching for the elusive 16 ohm Ohmite rheostat. I did find a 15 ohm rheostat, made by a different company, but had similar dimensions. I may try and adapt that one to my unit. At least I can connect it and see if it works. I'll still have to rap on the circuit board relat just to get things sarted, but I'll be able to see if the rheostat controls the wire speed motor.
              If it doesn't work, I know I can at least order the correct Ohmite rheostat from Mouser for far less than what I would pay Miller's parts dept, (sorry Miller!).
              Also, I placed a new post here looking for a printed circuit board from a 130XP. I'm hoping maybe someone here may have a trashed unit with a salvageable PC1 board in it.
              Wish me luck!
              Last edited by docdeath; 05-03-2012, 05:51 PM.

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