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Bobcat 3 Phase Troubleshooting help.....No Weld Power

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  • Bobcat 3 Phase Troubleshooting help.....No Weld Power

    I've got a Bobcat 3 Phase. I don't have the complete serial number on me but it is LJ0xxxxx series newer machine.

    It starts fine, idles good. It is generating 115Ac power at the plugs, and the run idle works correctly when you apply power at the plug. The welding output will produce a light arc (enough to burn the tip or stick the electrode) and the machine will idle up to full power but will not weld.

    I have replaced the F1 and F2 fuses.

    I have OCV on the weld outputs of:

    CC + and - of 26.8V
    CV + and - of 26.8V
    AC @ 30V

    The brushes are showing 16V.

    Is there are good starting point to troubleshoot this machine?

  • #2
    Post the WHOLE friggen serial #, so I can bring up the correct diagram in the service section.


    • #3
      Yep. SN#LJ200170H.


      • #4
        what is the condition of the slip rings, are they both real dirty, or does one look clean while the other dirty. A brush may not be making a good contact


        • #5
          The slip rings both look bright. I'll check the brushes again. Is the voltage I'm reading correct?


          • #6
            Not even close. What does the Auxillary read, and what is the frequency high idle no load.


            • #7
              I dont know how close the machines are, but I have a Trailblazer 275 that had the same problem. No repair shop could figure out the problem. I finally decided to try to figure it out....... Long story short, it had a broken rocker arm in the engine. Causing 1 cyclinder not to fire. It would rungreat, all the electrical checked out ok, but once a load was put on it, it would not weld. I replaced the rocker arm and it has ran/welded perfect ever since. Just my 2 cents.


              • #8
                Aux Power is

                114V @ 58.6hz
                229V@ 58.3hz

                I used some alligator clamps on the brush leads and recorded 23.6V on the brushes. I may have not had a good connection on the previous voltage test. I was a little nervy with my hands down in there with it running.


                • #9
                  Yep freq is WAYYYY low, Must be 62.5Hz high idle no load.


                  • #10
                    Originally posted by cruizer View Post
                    Yep freq is WAYYYY low, Must be 62.5Hz high idle no load.
                    OK. I adjusted the run speed to 62.6hz @ 126v on the Aux. However, I still have no weld power. It's like welding with 30 amps instead of 150 amps. The rod will arc or stick but will not burn steady.


                    • #11
                      Whats the DC+ OCV now??


                      • #12
                        DC+ voltage at 28.3v at run position OCV


                        • #13
                          whats the AC output at the studs in dC+ mode. I'd say that your rectifier is pooched.

                          Not usually a winding issue.


                          • #14
                            The DC+ AC voltage is 11.8V at run speed.

                            If it is the rectifier, any way to repair a rectifier without purchasing a new one from Miller?


                            • #15

                              Anybody know how to test the rectifier?


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