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Miller Big 40 won't weld no AC

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  • Miller Big 40 won't weld no AC

    Hi I have A big 40 that I can't get no arc or ac voltage I have tried cleaning slip rings, flashing fields and have checked ohms from slip rings which I thing was about 48 form center to back and about 13 center to front. Also checked stator windings which I think is #50 to 51 #3 to 4 and #1 to 2 which was all 1 to 2 ohms If I plug in a grinder and apply 12v to wire 5 and 6 the grinder will run very slow until I take away the 12v. I did find the s/n which showed it to be a 1978 but some wire #s and it showed the block to change to 240v which this don't have so I use a manual from 1976-77 which matched perfect so I believe the front panel has been changed. The manual I used was 450d from miller site. I was thinking main diodes but wanted some more ideas. Would appreciate any help. Thanks very much.

  • #2
    wires 103 and 104 also.

    SR 1 rectifier readings
    Attached Files
    Last edited by Popscott; 06-19-2018, 09:14 PM.


    • #3
      Ok I have checked the rectifiers and I believe the both sr1 & sr2 are bad so I have them ordered. Will see what happens then. Sorry for not answering sooner but also working on changing a motor. Thanks for the help.


      • #4
        I have a new HF 251 High freq box for ac tig aluminum.