MM175 : Can't kill it...HELP

[MAC702]

Okay guys, You might remember I had to work on the trigger of my MM175 before. Well, new problem now: half the time when I let off the trigger, it won't stop welding. It keeps feeding wire and stays hot.

I've disected the trigger again, and it looks absolutely fool-proof. I've even insulated the terminals so there is no way it is shorting against anything inside the gun. The trigger is not sticking anymore, it comes all the way back off, and there seems to be no way for it to not break the connection when it does so.

Any ideas? I know that if the problem is in the trigger, the gun is out of warranty. But I'm wondering if it might be in a relay somewhere, in other words, in the box, which is still under the 3-year warranty, right?

I opened the box and could see nothing obvious, so went no further until hearing from the experts.

I'm in the middle of a job where this is the machine of choice, so time is an issue

[ASKANDY]

MAC,
When the wire starts running out of control, can you disconnect the trigger from the machine and the wire stop??

If so, then the problem is still in the gun and the trigger lead might be shorting to the gun power cable inside the lining somewhere. This may be intermittent depending on how the gun is placed. There is a relay on the main control PCB that is part of the trigger circuit and could be the culprit also.

Let me know.

Andy

[moe1942]

MM175 not cutting off

I'm no expert but if you have had trouble with the trigger switch before I would change it. Should not cost very much in comparison to the aggravation you are experiencing. Also, If you have a VOM you could ohm it out before buying a new switch.. Keep activating it and see if you can make it hang up.

If the trigger isn't the problem you could have a contactor hanging up. The trigger energizes the contactor which in turn gets the inards churning and burning. If the unit is still under warranty it might be best to take it in for a quick fix.

I have had contactors in central air units hang up. The contacts get burned after repeated use. Same principle in MIG welders. I wouldn't recommend working on the internal components unless you have a good working knowledge of electricity. The life you save may be your own.

[MAC702]

Actually, my wife and I are also both electricians, and I've repaired many welders, including my recent PowCon, with new electrical components, but I'm first going to find out if its on my end (gun, out of warranty) or theirs (box, under warranty.)

I like the VOM idea, I think I'll try that tonight.

Andy: Also a good idea. I'll try both of those ideas tonight and try to isolate where the problem is.

[timw]

I'm not familiar with the 175 but if the Mig cable has the small wires that plug into the front of the machine you can unplug that plug when it's stuck on and that will disconect the trigger circut outside the machine. If it continues to run it's inside and possibly a contactor sticking.

[MAC702]

Okay, it did it again yesterday afternoon, and it was kind enough to stick long enough so that I could yank the plug and it would stop, put the plug back in and it would go again. This confirms that it is in the trigger or wiring to the trigger.

I pulled the trigger out further than I ever had before and looked at as much of the wiring as I could. It had some flattened spots in the insulation, from where they were twisted around each other, but didn't really looked damaged. I carefully rewound them without twisting them and replaced the trigger. So far so good, but I've been there before, too.

[ASKANDY]

MAC,
Is that the standard MILLER gun??
If so, send me your address by regular e-mail and I'll send you a new gun. I hate seeing all the trouble you are going through.

Andy

[MAC702]

Yes, it's the standard gun. Thanks a bunch, this has been quite frustrating.

And to everyone else still wondering which welder to buy, this is a good example of why I buy nothing but Miller.

[MAC702]

Only now do I feel dumb. I can't figure out how to E-mail you.