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Miller big blue 400 amp control

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  • Miller big blue 400 amp control

    Hi, I have a big blue 400 pro 2015 model with 3300 hours on it. I bought it several months ago mostly as a home backup generator but with the option to also weld. I did some motor maintenance with filters and fluids and while I was at it I decided to change the brushes and stone polish the slip rings as the brushes were fairly worn down. A buddy of mine came over and did some welding today and said it's basically arc gouging putting out max amps even though the amperage selector shows it increasing and decreasing when he adjust it, no matter how low he sets the machine, if he sets it to 70 amps it's welding like its maxed out when he strikes his arc. What in general would cause this issue? Thanks

  • #2
    get a copy of the owners and parts manual with your serial number.

    Look at trouble shooting guide.

    Check out OCV relay CR7

    Call tech support


    • #3
      The serial number would help a lot on that welder. Miller made like 12 models of the big blue 400.


      • #4
        Serial number MF410006E
        Last edited by chilbun28; 02-22-2023, 01:12 AM.


        • #6
          I brought the machine into the shop and dropped it off. While I was there the mechanic performed several test before we unloaded it. He pulled out a Miller diagnostic machine of some sorts and hooked its leads from his machine to the welder and performed several test. he was thinking it was the LEM, so he unplugged the LEM and ran a test and recognized it wasn't the LEM. He looked at the IGBT and it had green lights on both sides of the module and when it was load tested another light came on which satisfied him the IGBT was good. He said the welder was doing exactly what my welder friend said it was doing, going full output on the DC side although the machine would read how ever many amps we would have it set at. He is thinking it may be the computer so he will be digging into it deeper over the next several days. Everything on the AC side is putting out like it should. Any Ideas?


          • #7
            It is most likely the main control IGBT gaiting module 265327 at a meager price of 1,741,62.....


            • #8
              Oh my......