Millermatic Challenger 172 Wire Feed Issue, help!

[Chuck S.]

New to forum! I see some help was given reference a couple of machines but not to this machine specifically (that I could find!). This is an older model obviously but with light usage. My wire feed quit while in service. Tested the 24 volt feed motor with 12 volts (all I had to work with) and it runs fine. The relays are both clicking and working. The big one that takes the power leads clicks on and then right off. Tried "helping" them stay on for a brief second, but no feed. What makes this bad is that this is a friend's welder who loaned it to me and I really need to get it fixed. Any help would be greatly appreciated, thanks!

[M J Mauer]

Chuck welcome to the forum.

[cruizer]

We as techs really need that serial number, both to confirm correct wiring diagrams and to see if there were any updates for this model

[wayne50]

Just wondering, did you get the problem resolved?

[Chuck S.]

Not figured out or fixed yet! But I have the numbers!

The stock number is 907000. The serial number is LB191380. Any help would be greatly appreciated.

[Miller Kevin]

Chuck,

The first thing you will want to do is try a different tap on the front of the unit (the 4 position heat selector) if it is in between selections it will do exactly what you are describing.

If that isn't the issue then we would need to find out if the unit has weld output or not. Put a meter set for DC volts right across the 2 polarity links above the wire drive and pull the trigger.

Let me know what you find and we can go from there.

[Chuck S.]

Tried it...

No feed on any of the speed settings. No DC from the leads. Thanks for jumping in on this.

[Miller Kevin]

Well there are a number of things that could cause this. You have no weld output so the drive motor will not run and the little contactor will not stay engaged either. The heat selector switch, main rectifier or the contactor itself would be the place to start.

If the gas valve is pulling in when you hit the trigger you can rule out the contactor as the cause. After that someone will have to go inside the unit and do a live measurement to check for AC to the rectifier. That will let you know if the heat selector switch and main transformer are working.

[Chuck S.]

Okay...

I can observe the gauge on my tank fluctuates when the trigger is pulled so I am guessing that would indicate the valve is working okay. I have the cover off because I "assumed" the drive unit was the problem and took it out. That's when I put 12 volts to it and found it ran fine so I put it back in. I also "bypassed" the speed control unit, putting the wires together for a second, figuring that would surely get power on to wherever it needed to go. That didn't do anything. I could test around in there with maybe a bit of help. I can't remember if I noted the fuse on the board was okay too, because I read somewhere that could have been an issue. Can you help me a bit more so maybe we can pin this down? Thanks!!!

[Chuck S.]

Pardon my "duh" moment...

Re-read your post. Didn't PULL THE TRIGGER when testing across the leads, duh. I just went back and did that, and get the briefest of power until the relay(s) click off. Varying readings, from like .01 to 8 and even 11 (meter set on 200 dc). Hope that helps to tell us something!

[Miller Kevin]

If you were measuring the feed to the rectifier that would be AC volts and you may have to hold the contactor in to get a measurement.

[Chuck S.]

okay...

I was going back and doing what you said the first time, measuring above the feed with dc. I am unsure how to measure the ac as you just noted. Will try if you can walk me through it.

[Chuck S.]

Checked AC to rectifer...

Through a YouTube video I was able to figure out how to check the AC going to the rectifier. The video said, in that case, he was looking for about 30 volts. I get zero. That is assuming I did it right, checking across the two large wires coming from the (large) transformer to the rectifier. Transformer bad? But still has power to fire up the fan and gun, etc.? Thanks for your help. Electrical things are not my forte.

[Miller Kevin]

Chuck,

Before you condemn the transformer the selector switch should be checked.

[Chuck S.]

Selector, a thought...

Since there is two wires going to this, wouldn't my short bypass attempt show that the switch didn't make a difference? But like I said, I am in over my head here and I have decided to take it in to have it checked.