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Another MM135 with wire feed issues

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  • Another MM135 with wire feed issues


    New to the forums and pretty much a welding noob! I have a Millermatic 135 that's probably 6-8 years old with very little time on it. Great it, but it has developed a wire feed issue. I have been all over the web reading plenty of cases, but can't seem to find the solution. Hoping you folks could help.

    The symptom is simply this. When I pull the trigger it will weld/feed for a few seconds, and the motor looses power/quits feeding. First off...its NOT the tension assy, wheel, liner, etc...I have narrowed it down to an electrical issue. The more load the motor has on it (coiled cable, tip install, etc) the quicker it happens. No tip, cable straighten out, it will feed awhile longer. Motor removed from cases, it will operate for several minutes before dying out. If I pulse (stitch weld) it happens quicker.

    At the board level, I hear the relays operating, the red led comes on when triggered. The speed and power pots seem to be doing their job...

    Any ideas? I have the capacity to check/replace board level components but don't know where to start.

    Thanks in advance for any words of wisdom!

    Last edited by Crash Odle; 10-12-2011, 11:37 AM.

  • #2
    As with all machines I kinda need a serial#, also make sure your not in between ranges as the output wire speed depends largly on the position of the output selector.


    • #3
      Thanks for the quick reply! The problem exists consistently throughout the speed selection range.The wire speed/motor speed seems to be properly regulated by the speed pot...until it quits that is.

      Millermatic 135 S/N #LB209564.


      • #4
        These units had a few problems with the gear boxes, best to order another motor/gearbox part # 202708


        • #5
          Originally posted by cruizer View Post
          These units had a few problems with the gear boxes, best to order another motor/gearbox part # 202708
          The problem isn't mechanical. I have had the gear box apart, and the motor removed. The problem happens, albeit longer to occur, while running the motor all by itself.


          • #6
            the motor will come complete with the motor and gear box


            • #7
              I'll check Vin to the motor tonight, but I suspect its a board level issue...not a motor issue.

              Another symptom, while I hear the gas begin to flow when the trigger is 1st engaged, I don't think it continues to flow (not hearing it and the weld isn't clean)


              • #8
                either the motor works or it doesn't there is no in between when it comes to a failed motor board.


                • #9
                  I agree with Cruizer on this one. If the pcb is bad, usually the motor will either work or it wont.

                  Just a thought.. but are you running this machine on a long extension cord?
                  Sounds like a power drop somewhere.



                  • #10
                    No extension cord...and some bad info...the gas is flowing.

                    I checked the voltage and its ~1.6-1.8v with the motor plug in (under load). Motor unplugged and checking voltage from the board it's ~25v. And the power doesn't drop off significantly when the motor stops. So as you both have indicated...a bad motor I presume. Is the fact that the volts are so low with the motor plugged in an indication of high amperage...a bad motor drawing a lot of current?

                    Another question...should the big blu cap mounted to the floor of the unit read 35v DC as indicated by its marking? I am getting .05v DC.

                    Really appreciate all the help! I miss having my lil' blue welder up and running!


                    • #11
                      When the unit is turned on, and trigger depressed the cap will charge to around 24 volts or so.


                      • #12
                        Copy that!

                        So I just hooked up my motor to a 12v DC power source and it ran...and ran...and ran. Plugged it back into the unit and it runs for a short period a craps out.

                        Some folks on the Hobart site in some older threads reference a bad Thermistor at PTC1 as the culprit. Ever heard of such a thing?


                        • #13

                          The PTC on the board is basically a heat activated circuit breaker. It is supposed to shut the motor drive circuit off if the motor draws to much current to protect the board from damage.

                          I have encountered cases where this device can get sensitive and prematurely shut the motor off. If the motor is not drawing high current then a failed PTC is most likely what is causing this issue.
                          Kevin Schuh
                          Service Technician
                          Miller Electric Mfg. Co.


                          • #14
                            Just wanted to follow up with an update. Went ahead and ordered some parts from Digi-key and I am happy to report that the culprit was the PTC. Just finished up a little project and it feeds like the good 'ol days!

                            For those with the same issue, eliminate all the mechanical items (liner, wire tension, etc) and before replacing your board, try replacing the component at PTC1 on your board. Less then 2 bucks, 3x times that in shipping (worth every penny), and 10 minutes to solder it in.

                            I'm just glad to not have to buy a $350 board for a $350 dollar machine!!!

                            Thanks to everybody for your help and input!


                            • #15
                              Can you advise the part number from digi key for the new part? I have the exact same problem
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