Millermatic 175 question

I have had my son's Millermatic 175 here for some time now. I last used it about 3 or 4 months ago and it worked great. Today he comes over to
weld some small stuff and it don't work. Crap! Turn it on and nothing happens. The internal fan comes on, but it is far from being up to full speed. No gas flow and no wire feed.
I took the cover off and didn't see anything wrong. All wiring seems to be clean and secure. I didn't mess with the capacitor at all, but everything else was ok. No burn marks that I can see on the circuit board and the green light comes on. Guess I'll ave to take it in for service.
This machine is a few years old and has seen very light use. Not even a full spool of wire has been run through it. Maybe 1/2 a spool. Not even any scratches on the thing. :-) I am suspecting that the circuit board has gone bad so here is the question. What should I expect when I take it in for repair? I am assuming that it will most likely be the circuit board since I have seen in a couple of forums that this is a somewhat common problem with this machine, but the symptoms they list when this happens are slightly different. Are there any other problems that you know of that might cause this?
TIA,
Wayne
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Really dumb question----It's wired 220 single phase, correct? Do you have juice to both L1 and L2?
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It may be a dumb question, but I didn't really have the time to do a whole lot of diagnosis. The kid was ready to leave and he wanted to take it with him. When he wants to go, he wants to go NOW. So I can only **assume** that L1 and L2 both have juice. I will have to go over to his place now to find out.
And you are right, it is 220v 1ph. I unplugged my dryer and used that outlet for the welder which I have done several times before. I have a good extension cord of about 50' of nice heavy wire which I think is 10ga. but might be 12ga. but it is heavy duty stuff and has not caused any problems in the past.
So let me ask you this. IF either L1 or L2 does not have juice, would that fan even come on at all???
Thanks,
Wayne
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NoOne N Particular wrote:

One suggestion is to vigorously flip all switches and controls through all positions a couple times, then back to where you want them. One of the selector switches or pots may have gotten a dirty contact and prevented the rest of the logic from completing.
Jon
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Been there. Done that. Disconnected everything that I could easily disconnect and reconnected too. Inside and out. But thanks for the tip anyway.
Wayne
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NoOne N Particular wrote:

Seems to me that normal electronic debugging techniques would apply. Plug it in, turn it on, and start checking voltages with a voltmeter. Check that the wall voltage is indeed reaching the welder, and if so start following it through. Most electronic failures are from power not getting where it's supposed to go.
Grant
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On Tue, 27 Nov 2007 11:30:06 -0800, NoOne N Particular

<snip>
Do you have the manual? If not that would be a good place to start. Miller has good manuals and downloads for free. I think you need either and/or one of these:
http://www.millerwelds.com/om/o1324c_mil.pdf
For "MILLERMATIC 175 M-10 Gun" (~1mb)
or
http://www.millerwelds.com/om/o1324k_mil.pdf
For "MILLERMATIC 175 W/M-10 GUN (~1.4mb)
A quick check in the first manual gives this under trouble shooting:
No weld output; wire does not feed; fan motor continues to run. Check:
-fan Thermostat TP1 open (overheating). Allow fan to run with gun trigger switch off; thermostat closes when motor continues to run. unit has cooled (see Section 2-2).
-Secure gun trigger leads (see Section 3-1).
There is a block diagram for the circuit board with input/output leads labeled (page 29). It sounds like it might just be a bad gun trigger switch or a problem en route to the circuit board for same.
--
Leon Fisk
Grand Rapids MI/Zone 5b
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I did have the online manual and I went through it AFTER the kid took the machine home with him. But it sounds to me like the part "fan motor continues to run" means the fan is running full speed. This fan is probably not even running at 1/4 speed. It was running so slowly that we could not hear it until we got our ears down to the rear of the machine and then it was barely audible. I'm hoping that his next day off he will bring it back and I can "play" with it more, and then most likely take it in for service.
Thanks,
Wayne
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On Wed, 28 Nov 2007 16:50:20 -0800, NoOne N Particular

Having never heard/seen one of these in action before I can only make some suggestions.
The circuit board schematic is a mystery, sadly Miller doesn't want to publish that part. It is possible that the fan motor is designed to ramp-up speed as needed by control on the circuit board. It may also just hook to the incoming mains. It is listed in the parts breakdown as 230 volt, so it may be possible that you aren't getting the full 230 volts to the circuit board. Check that area and make sure you have 230 volts getting in to the unit (be careful, 230 volts probably won't kill a healthy person, but it ain't no fun getting zapped) and making it to the PCB. The fan running at only 1/4 speed kinda points to this area.
If that checks out, make sure the trigger switch on the gun is actually getting to the PCB too. Just because you can hear a little clicking noise when you pull it doesn't mean that it actually makes contact.
If that checks make sure that the thermal protection sensor coming from the transformer is hooked to the PCB.
If that checks and you want to try messing with it further, take some GOOD pictures of the PCB and post them someplace where I/we can look at them. From looking at the block diagram it (PCB) really doesn't seem to be all that complicated.
Good luck and let us know how you make out.
--
Leon Fisk
Grand Rapids MI/Zone 5b
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Leon Fisk wrote:

Thanks for the tips. I went over and got it back from the kid today so I may be able to do some more testing this weekend. Just to clarify a couple of things:
1. I think the fan is supposed to come on full speed at all times. It always has before. Hit the switch and the fan comes on and stays on. Never have heard it run at different speeds. 2. The trigger switch on the gun does nothing. No sound at all. No click, no gas, no nothing. With the exceptions of the fan running at a very slow speed and a green led on the circuit board, it is as if the machine isn't plugged in at all. 3. When I had the cover off, I did at least check to make sure everything was connected. The thermal overload was connected and it was not tripped. I disconnected all the push-on connectors and re-connected them a few times just to see if there was some corrosion that may have prevented one from making a good contact. Did the same for the gun controls.
I have also read a couple of other forums and one or two people have alluded to a problem with the circuit boards on some of the early 175's. One even said that there have been 2 or 3 revisions to it. I will also have to track down the serial number and see when it was made. It might be one of "those" machines. That would be my luck.
Thanks again.
Wayne
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On Thu, 29 Nov 2007 17:23:20 -0800, NoOne N Particular
<snip>

I tend to agree with your assessment here (fan full speed). It may just be a bum on/off switch or something keeping the full 230 volt from reaching the circuit board. When you get it opened up again carefully measure the voltage and make sure you have ~230 volts.
If that checks out take a good look at the circuit board and follow the fan traces back towards the input source and look for burnt traces or anything else suspicious looking.
The fan on my Millermatic 200 is thermostat controlled and always starts up kinda pokey when called for. I figure it is just a lube problem in the fan (worse when it is colder). Your fan may be okay and have full voltage if you didn't try running it for very long.

The manual tells how to change the switch in the gun. Which makes me a little suspicious that it does fail at times. It looks like it just plugs in via blade connectors, should be easy to bypass/check (short the blades together with a screwdriver :).

I noticed in the manual that they had 3 sets of numbers referencing the board, so indeed they may well have made some changes :)
--
Leon Fisk
Grand Rapids MI/Zone 5b
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