Miller 251 questions

[indyanajohns]

I am new to the forum and just picked up a used Miller 251. The machine came with no cord, ground or gun and I could not test the machine in any way but the cost was only $150. I made the gamble and brought it home last night and opened it up. I briefly installed a temporary power cord and the machine does come along with the display. I am now tracking down some of the missing parts. I have a few questions,

-The inside of the unit is covered in a very fine silt dust that will not simply blow out with compressed air. Should I try and wipe out as much as possible with a dry rag? Should I pay close attention to cleaning any particular part that would be sensitive to dirt/dust?
-When I install the new power cord I understand the two hot legs connect to the back side of the on/off switch, I don’t see an obvious location for the ground wire? I tried looking in the manual but the wiring schematic is way over my head.
-I already have a 300amp rated ground clamp but no cord. What size wire should the ground clamp use if I have a max 15’ length? What is the name of the wire, I know it’s a finer copper strand that typical wire I have seen.

Thanks for taking the time to answer a few newbie questions. I can post pictures later tonight if it helps?

Josh

[morgaj1]

Good find. Someone more knowledgeable than me will be along to answer your questions.

[norite]

If the machine had the gun, ground lead and power cord removed it may because it had a major problem which was too expensive to be worth repairing. Be sure to test the wire feeder, controls and welding output before you invest in a new gun to put on this unit. If you don't know how, take it to someone who does.

You can brush carefully with a paint brush dipped in isopropyl alcohol if necessary, then blowing with compressed air. Try to just loosen the dirt so it can be blown off, don't apply too much alcohol causing it to run into tite places carrying the dirt. Whatever won't come off will probably have to stay there, could be paint overspray which is very difficult to remove.

The ground wire in the power cord should connect to a lug on the frame/housing of the welder and should be somewhere near where the cord enters the machine. If not install your own lug.

For the work ground it should say in your manual what size is required, guessing 1-0 or 2-0 awg welding cable is adequate, depends on the duty cycle of the machine.. If you don't have a manual, they are available from the manufacturer online as a pdf file. Download it and print it out, it will answer many of your questions.

good luck and welcome to the WW forum.

[Heliarcman]

First I would go to the Miller web site and down load the manual to the 251:

http://www.millerwelds.com/service/ownersmanuals.php

Before you buy a mig gun, you can test the unit for open circuit voltage by jumpering the torch switch at the torch swith connection on the front of the welder. With a volt meter set to DC place your probe on the (+) & (-) inside the side door where the ground hooks to and the connection to the drive rolls. You sould see a voltage around 16-22+ volts DC. With the torch swith jumpered out you can also test the feed system. Run the wire feed speed up and down to see if it works.

If that works, go buy a mig gun.

You can find an inexpensive mig gun on ebay. anything with a miller rear connection will go on your 251:

http://cgi.ebay.com/Miller-Tweco-200...item35aacd1663


For a ground cable you don't need much over a #2 welding cable. I think Miller uses a #4.

Put it all together and fire it up!

If it works out....YOU got a great deal!!!!!!!!!

[Broccoli1]

Originally Posted by norite

For the work ground it should say in your manual what size is required, guessing 1-0 or 2-0 awg welding cable is adequate,

I would say 1/0 or 2/0 would be adequate

Might wanna try #2 first though

[DirtyOz]

If it proves to be not worth repairing, maybe you can get the money back in
scrap copper!

[indyanajohns]

Thank you all for the advice, sorry for the slow response it was a busy weekend with the family, fun and an ER visit…

Helialarcman-

I would love to test the welder before buying a gun and appreciate your approach. I am somewhat a novice when it comes to electrical issues so I want to be sure I fully understand the testing method,
-When you say “jumper” the torch switch you’re referring to the mig gun connection. The mig connection has four holes only two actually have metal pins for a connection so I would bridge the two pins with a scrap of wire?
With the mig gun switch jumped I would then test the + and – terminal inside the welder?

I just want to be sure I am not misunderstanding how to jump the torch switch, I don’t want to damage the machine or myself!

I called our local welding shop about testing the machine and it’s a minimum one hour charge if not two. I figure for that price I can buy a gun off ebay test it and if it does not work sell the gun again and be out less than two hours.

Thanks again for the advice,

Josh

[SundownIII]

Josh,

Based on what you've said, I'd be very suspect of that particular machine.

The fact that the gun, work lead, and power cord have been removed would lead me to believe that the previous owner knew there was a problem, probably had it checked out, and tried to recover "what he could".

I'd throw a temp power cord (8/3 would be plenty) on it and fire it up before I went any further.

The owner's manual will show where the work lead attaches inside the machine. As mentioned, a 2ga welding cable (with lug and ground clamp) will work fine. 1/0 or 2/0 would be GROSS overkill.

A Bernard Q-300 would be a great gun for that machine (that's what I use). If you find the right deal on flea-bay, you can often pick them up for <$100.

[indyanajohns]

Sorry for the slow progress and updates on my post. I have 11 month old twins and a three year old so my free time in the shop is extremely limited

I jumped the mig gun contact and the drive motor does not engage. I can measure output at the -/+ welding leads and I can hear the gas regulator clicking on and off. I kind of doubt the drive motor is bad so I assume the PC board is not sending power to the drive motor. I will try and test the drive motor directly next, it’s labeled 24v so I am borrowing a power supply to test it. If the motor is good it’s down to the PC board. If I knew the board was the only issue I would bite the bullet and spend the $350 on a new one but I don’t want to invest the money and end up with two fried boards.

A friend with circuit board experience is going to take a look at the machine this weekend, does anyone have any thoughts or hunches on the problem? I know trouble shooting PC boards is very difficult but I am guessing someone has had this same issue in the past? I will probably have my friend speak with Miller tech support after he has looked over the machine. Does anyone have any thoughts, recommendations or hunches on the potential problem?

Thanks again for the help,

Josh

[Thiel-Metal-Fab]

i just repaired a millermatic 251 @ work , wire feed motor wasnt operating , it ended up being the wire feed control board , the board was not very big , but i believe it was around $200.00 ..........

[pullemfar]

Originally Posted by indyanajohns

I jumped the mig gun contact and the drive motor does not engage. I can measure output at the -/+ welding leads and I can hear the gas regulator clicking on and off. I kind of doubt the drive motor is bad so I assume the PC board is not sending power to the drive motor. I will try and test the drive motor directly next, it’s labeled 24v so I am borrowing a power supply to test it. If the motor is good it’s down to the PC board. If I knew the board was the only issue I would bite the bullet and spend the $350 on a new one but I don’t want to invest the money and end up with two fried boards.

A friend with circuit board experience is going to take a look at the machine this weekend, does anyone have any thoughts or hunches on the problem? I know trouble shooting PC boards is very difficult but I am guessing someone has had this same issue in the past? I will probably have my friend speak with Miller tech support after he has looked over the machine. Does anyone have any thoughts, recommendations or hunches on the potential problem?

Keep us posted on this, I just got a MM251 that is bare bones, and looks pretty dang new. I'm sure theres something wrong with it, just done no testing yet. Going today to buy a power cord, fingers crossed.

[soutthpaw]

Originally Posted by Thiel-Metal-Fab

i just repaired a millermatic 251 @ work , wire feed motor wasnt operating , it ended up being the wire feed control board , the board was not very big , but i believe it was around $200.00 ..........

e

I had the wire feed board go out on my Migmaster 250, got it repaired for a flat rate of $84+ shipping at Innovat corp. they have a price list online you just need the part number off the PCB

[pullemfar]

OK, just put the power cord on and the welder turns on and the display works, so this leads me to my first question. Is the cooling fan suppose to come on once the welder is turned on or after a bit of time of use?

UPDATE: Just tested the wire drive, it works fine throughout the whole speed range. However I tried testing the +/- with the torch switch jumped and nothing. I checked it at the power switch and got a 25-28 reading and checked the bottom side of the switch and nothing. I checked it at jumper links and it tested at 25-28. I guess i"m checking it right, my voltmeter has all these frigging symbols and i'm no dang electrician. I my set craftsman voltmeter on VDC auto and 25-28 is what it read so, i guess its right. Still no fan action though.

Anyone care to take some pics of this whole testing procedure (points etc...), I'm tight with the dough, so all I can accomplish myself is a +.