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35 year old bobcat welder no longer welds or generates power

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  • 35 year old bobcat welder no longer welds or generates power

    I have an approximately 35 year old bobcat 225 welder that no longer generates power or will not provide enough power to spark a weld. I can drag a welding rod on a piece of metal and it barely sparks. It worked fine one week and then the next time I tried it, it didn’t. I’ve read some previous posts and just changed out both fuses, the rectifier, diode and capacitor. Still nothing. Any advice would be appreciated. TIA
    Last edited by GWBMJB; 06-14-2020, 05:26 PM. Reason: The serial number is KC220664

  • #2
    Serial number?

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    • #3
      Check the slip rings and brushes. Don't change parts without making sure they're bad first - it rarely fixes things!

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      • #4
        Originally posted by Bushytails View Post
        Check the slip rings and brushes. Don't change parts without making sure they're bad first - it rarely fixes things!
        And clean the wiper blades on the reostat and the Selector switches and these guys need the serial number.

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        • #5
          Originally posted by Aeronca41 View Post
          Serial number?
          Serial number KC220664

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          • #6
            Originally posted by Bushytails View Post
            Check the slip rings and brushes. Don't change parts without making sure they're bad first - it rarely fixes things!
            Do you have to replace the slip rings or is there a way to re-polish them?

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            • #7
              Originally posted by GWBMJB View Post

              Do you have to replace the slip rings or is there a way to re-polish them?
              Unless they are just pitted/fried beyond recognition, just polish them up. Some people don't worry about this, but if you don't have a stone made for the purpose, use sandpaper, not emery cloth. Emery dust is conductive and you don't want it inside your welder. And check the connections to the brushes, and be sure the brushes can move freely in their holders.

              Check the fine current control closely for cracks or bad connections.

              Here's the manual if you don't have one.

              https://www.millerwelds.com/files/ow.../O431F_MIL.pdf

              Besides checking out the items already mentioned by others , check connections on R2, the big tapped resistor (Item 4 on page 43 of the manual). Loosen and retighten the connections.

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              • #8
                I've been known to use a strip of scotchbrite pad taped to the wooden handle of a wire brush if they just need polishing.

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                • #9
                  Thanks for all the responses. I polished the slip rings and changed the brushes even though I think they were okay. Still no power to weld or generator power. Any other things I can check. TIA

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                  • #10
                    Did you check the connections on the big resistor R2?

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                    • #11
                      Originally posted by Aeronca41 View Post
                      Did you check the connections on the big resistor R2?
                      That's the one item I check first with these ols Bobcats. Corrosion gets under the wiper

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                      • #12
                        I will check it and comment back. Thanks

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                        • #13
                          I checked the connections on the R2 resistor and they are all tight with no corrosion. As far as the wipers- what exactly is that? I did notice that there is some black substance on the S1 switch blades as well as the S3 switch selector. I don’t know if that’s normal or not? Any help is much appreciated.

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                          • #14
                            You need to remove, clean, and reconnect the wires on R2. Corrosion can get underneath especially the moveable band and kill the connection. Mark where the band is, take it off, clean it and the resistor underneath with a wire brush or sandpaper, and reassemble. The wiper is another term for the metal band on R2 that allows it to be adjusted by moving the metal band.

                            Switches with black stuff on them can generally be made to work just by working them back and forth through their operating range a dozen times or so.

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                            • #15
                              Okay, thanks for that info. I’ll do that and get back to you. Thanks again

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