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MM 350p

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  • MM 350p

    So I let a buddy borrow my 350p for a quick job. He noticed it made a little buzzing noise from the contactor which I new about just had not got around to replacing or cleaning it. He decided to replace it to thank me for the use. Well I'm certain its not wired correctly. It comes on as normal, everything works. As soon as the trigger is squeezed everything seems normal for about 5 seconds the a little puff of smoke comes right around the white plug in on I believe PC2 on left side close to the large resistors. I know the l1 and l2 input are correct as I done those before. I'm assuming the small wires were wrong. I checked the diagram on the machine and rewired what I believe to be correct. Same thing. Does any one have a clear pic of the to and bottom of the contactor to make sure? I did run a power up test and got to th IGBT's and everything tested good but didn't have the tester to go any farther. Thanks!

  • #2
    We have to start someplace. Are you sure the contactor is a 60 amp 24 VAC coil? I assume you're running single phase. Wires 3 and 4 must be hooked to your black and white input legs connected to the contactor. The only other 2 wires i see are the coil wires. Every Miller the wires are #ed. What wires are you unsure of? I think you better take an OHM reading on those big resistors.


    • #3
      The contactor is 60 amp 24 VAC. Single phase. Wire # 1 and #2 are conncted to the bottom of the contactor at L1 black and L2 white inputs. Wire # 27 and I believe # 28 ( the 2 is partilly rubbed off, the 8 is very readable) are connected to the top of the contactor on the left and right posts furthest to the rear. The large resistors R11 and R12 ohmed out correctly at 40 ohms.If fact all the same size resistors on that board ohmed out at 40 ohms.
      Last edited by Opel; 01-20-2021, 09:43 AM.


      • #4
        The other side of the contactor connected to L1 should be #3, L2 should be #4. I don't see where you've done anything wrong yet. That buzzing noise might have been a low voltage supply but without measuring I can't tell for sure. Have you checked the pins in that plug that wisps a bit of smoke?
        Does the machine work or you shut it down as soon as you see smoke?


        • #5
          I dont have a #3 or #4 there just the #1,#2,#27and #28. 27 and 28 are going to the 24 side of the contactor I assume to pull the contactor in to start welding. I have not tried to weld with it. I actually hit the trigger to get the gas flowing and thats when I noticed a little puff of smoke, and I let off the trigger immediatley. Nothing I can see is burned and that 9 pin plug looks good.I even installed the old contactor and same thing. Thanks!
          Last edited by Opel; 01-22-2021, 10:48 AM.