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Thread: Miller Big 40 continental gas engine wont weld

  1. #1
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    Miller Big 40 continental gas engine wont weld

    First post, new to this. I have a 1985 miller big 40 machine and it randomly quit welding without any sign of it quitting. Crunk it up one day and it would barely arc up. Wide open amperage would barley hold an arc. Took it to a local shop and they diagnosed it as being the diodes. I replaced all 6 not paying attention that three were different me thinking they were all the same I need some serious help of finding out the orientation that the diodes need to go in.. ANY help would appreciated as Ive looked for weeks without any luck.

  2. #2
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    Re: Miller Big 40 continental gas engine wont weld

    Quote Originally Posted by CalebT View Post
    First post, new to this. I have a 1985 miller big 40 machine and it randomly quit welding without any sign of it quitting. Crunk it up one day and it would barely arc up. Wide open amperage would barley hold an arc. Took it to a local shop and they diagnosed it as being the diodes. I replaced all 6 not paying attention that three were different me thinking they were all the same I need some serious help of finding out the orientation that the diodes need to go in.. ANY help would appreciated as Ive looked for weeks without any luck.
    The first thing I'd suggest is your posting all the information from the Data plate, including the serial number. A good, clear picture might be the best way. Using that data, we should be able to download the manual with a schematic from the Miller website.

    Are the replacement diodes still uninstalled, or did they get put in wrong? I wonder if worn brushes might also have been part of the problem.

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    Re: Miller Big 40 continental gas engine wont weld

    Quote Originally Posted by Oldiron2 View Post
    The first thing I'd suggest is your posting all the information from the Data plate, including the serial number. A good, clear picture might be the best way. Using that data, we should be able to download the manual with a schematic from the Miller website.

    Are the replacement diodes still uninstalled, or did they get put in wrong? I wonder if worn brushes might also have been part of the problem.
    I will take pictures this evening, I have 110 power all day long. The brushes have checked out okay. I was told if you have 110 power then that would rule our brushes being an issues. They look to be in good shape on the other hand as well

  4. #4
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    Re: Miller Big 40 continental gas engine wont weld

    Page 17.pdf

    Diode Testing.pdf

    Look for the symbol on the side of each diode to determine their polarity and compare that to the wiring diagram to determine how they need to be installed in the weld output rectifier.
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    Re: Miller Big 40 continental gas engine wont weld

    I installed the diodes incorrectly. Sorry left that out. There are three of them that are different. I bought all 6 of the same and plugged them in. Did t take a picture like I should. Got in a hurry.

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    Re: Miller Big 40 continental gas engine wont weld

    Serial number is JF919101. Thanks. Any help appreciated. I havent been able located a wiring diagram to determine what diode goes where. I tried uploading picture but cant find where you do that.
    Last edited by CalebT; 1 Week Ago at 10:27 PM.

  8. #7
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    Re: Miller Big 40 continental gas engine wont weld

    PM me an email address and I'll send you the Technical Manual for your unit.

    You can download the User Manual here:
    https://www.millerwelds.com/files/ow.../O450M_MIL.pdf

    The subject diodes are on the right side of the Circuit Diagram shown on page 24, Figure 8-1.
    MM200 w/Spoolmatic 1
    Syncrowave 180SD
    Bobcat 225G Plus - LP/NG
    MUTT Suitcase Wirefeeder
    WC-1S/Spoolmatic 1
    HF-251D-1
    PakMaster 100XL
    '68 Red Face Code #6633 project
    Star Jet 21-110

    Save Second Base!

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    Re: Miller Big 40 continental gas engine wont weld

    Caleb11tucker@icloud.com that is my email. Thank you!

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    Re: Miller Big 40 continental gas engine wont weld

    Quote Originally Posted by CalebT View Post
    Caleb11tucker@icloud.com that is my email. Thank you!
    Caleb, if you click Duane's name in the top left of his last post, it will open a new window showing Duane's Profile and having a list on the left, the second item being "Send Private Message". Clicking that will allow you to correspond directly with Duane without having to give your Email address in a post where anyone else will see it, including spammers.

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  13. #10
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    Re: Miller Big 40 continental gas engine wont weld

    Email sent.
    MM200 w/Spoolmatic 1
    Syncrowave 180SD
    Bobcat 225G Plus - LP/NG
    MUTT Suitcase Wirefeeder
    WC-1S/Spoolmatic 1
    HF-251D-1
    PakMaster 100XL
    '68 Red Face Code #6633 project
    Star Jet 21-110

    Save Second Base!

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