Miller Electric

Welding Discussion Forums

Home » Resources » Communities » Welding Discussion Forums

  • If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.


Announcement Module
No announcement yet.

Millermatic 35 Wire Feed SLOW

Page Title Module
Move Remove Collapse
Conversation Detail Module
  • Filter
  • Time
  • Show
Clear All
new posts

  • Millermatic 35 Wire Feed SLOW


    I found a MM35 and hooked it up.

    The wire feeds super slow out of the Tweco #4 gun. The wire feed knob works, but even the 100% speed is too slow. It does not appear to be a problem with the gun liner. Feed motor brushes look good.

    I poked around the inside and 2 of the large diodes are shot, one open, one shorted.

    I'm replacing them tomorrow, do you think that the diodes somehow will also fix the wire speed problem?


  • #2
    Replacing the two 150A 300v reverse polarity diodes fixed the problem.


    • #3
      Hey just read your post.

      Just for clarification the large diodes do not affect the wire speed control circuitry. By replacing those 2 diodes you fixed the bridge rectifier that controls the DC voltage output that creates your welding arc. With those 2 diodes not functioning, your welder does not create the necessary voltage to make a hot enough arc to weld properly. You may have misinterpreted this as bad wire speed.

      I was just troubleshooting a MM35 that wasn't creating a proper arc, and I also felt that wire speed felt funky. After reading your post I decided to test the diodes for proper function. I too ran into 2 bad diodes. . . one shorted, one open. Thanks for posting your issue, it gave me a new avenue to test. That ended up being my power issue.


      • #4
        From what others have posted, the MM 35 powers the drive roller motor off of the DC welding output through a rheostat. So bad DC welding output will impact feed speeds.


        • #5
          Yes, the bad diodes really did slow the wire feed down to a crawl. Just looking at the drive gear spinning, I could tell it was way too slow.

          My local Miller dealer did not stock the diodes, so I got them from Galco for $18 each and they arrived 2 days later. The reverse diodes are part # 037-306.

          My dealer said they often fail in pairs. The first shorts out, then the other burns open when it can't handle the current by itself.

          The welder is flying now, built 1/2 a trailer today with it.


          • #6
            slow wire speed on a mm 35

            For 25 years I used .035 and .030 wire and this Miller matic 35 only welds at the 100 speed by lowering the speed---I just put a new liner---for .030 and it remains the same ----it only burns the wire back into the tip. Can you tell me how to diagnose and test the diodes -----and if you have a phone number ________of a source to buy them after testing is convincingly definitely the problem . Feel free to call me Thanks, Don 585-352-1165


            Special Offers: See the latest Miller deals and promotions.