Hi Folks! I'm a brand new member (and newbie welder too), with a broken MM 135 (Serial #LB265626; board # 199820). I've been reading through the amazing wealth of troubleshooting info you've all provided, but I've yet to fix my issue.

Short version: Wire isn't feeding. The motor won't turn, even without wire. Gun (or shorting gun connection) just generates a clicking relay (my troubleshooting attempts listed below). Motor does run with 12v power.

Long version: This unit was purchased used. Seller demoed it for me, then it sat for about a year in my garage before I got up the courage to mess with it. The machine was exactly how the previous owner had left it -- .23 wire, 75/25 gas, feed tension at 3.

It worked great for about 30 minutes (maybe 3-4 minutes of actual welding/bead time, though not continuous). After a bit of hunting around for some more scrap, I was ready to go again. At some point in there, I knocked the gun off my table and onto the ground. That maybe just coincidence, but the machine wouldn't feed wire when I started up again. (trigger causes click, but no motor action). I'm thinking I maybe damaged the tip and that jammed the feed and "tripped" some sort of protection (or burned some sort of circuit). But that's just a theory based on what I've read in a ton of 135/175 threads. Most of these are related to erratic wire speed issues versus my "no feed" situation, but hey, gotta start somewhere!

Here's what I've checked so far:

  1. Removed all tension from wire/gun leaving a naked feed wheel. Fed wire both ways through gun to check for kinking or blocked liner.
  2. Unplugged the unit and let it rest, thinking this would allow a thermal breaker to reset. However even without wire the trigger only generates clicks from relay (but doesn't spin motor).
  3. Removed gun from trigger recepticle. Shorted pins there. Behavior is just like gun trigger (clicks but no motor action).
  4. Checked power at terminals above wire feed mechanism. I set voltage at 5 and see 23 volts DC at terminals.
  5. Opened case. Red light comes on with clicking. Checked circuit board for good connections. Looked for obvious burning, bloating, etc. None found.
  6. Unplugged motor pigtail. Applied 12v battery power to motor side of connector. Motor (and gearing) spin fine.
  7. Checked continuity of PTC1. Closed. Jumpered (as best as I good -- this seems kinda iffy to get in there safely and effectively) and got same clicking result.
  8. Checked legs of Q1, Q4, Q8. No continutity between legs -- I *think* that is something I'm supposed to be checking .
  9. Q5 seems to get the most attention as problematic on the 135/175, but on this board, Q5 is a really tiny 1/2 round unit -- no heat sink like I've seen in most of the other thread.

Next step?: I guess I'll try to re-flow the solder for PTC1. I'm thinking a brittle joint could be causing it to act open. And maybe I'll order one and replace it for the heck of it.

But that's all I can come up with. The board is on my desk now. I'm happy to take measurements (I have an autoranging dmm, but no clamp for amperage -- I'll buy one though if that helps!), if anyone can point me in the right direction.

Thanks in advance for any help you can throw my way!