Lincoln square wave welder question

A fellow offered me a Lincoln square wave TIG welder. About 10-14 yrs old. He replaced all the boards etc..but it still has an Issue. No
matter what he does, it always outputs the full 400 amps. Makes it a bit hard to weld thin stock according to him. <G>
Evidently Lincoln sent him all the schematics and diagrams etc, but is not interested in helping him diagnose the problem. He claims he has about $1000 in all new boards so far. He is the original owner and it suddenly started not being adjustable.
Anyone have any idea of what it could be? This machine IS single phase, ac/dc/ stick/tig etc and would be just the ticket for me, but...Im sure not gonna do any horse trading unless its an easy inexpensive fix. Currently he owes me a BIG favor...<G> so ....
He didnt remember the model number but will call me tommorow with the info. Im not familiar enough with such things, let alone not being able to diagnose at board level such a critter.
He did offer to outright give me a Lincoln motor generator tig welder in running condition, but its 3 phase.
Any idea what it could be? I didnt ask, but I assume...assume he checked the pedal, etc. Gunner
Liberals - Cosmopolitan critics, men who are the friends of every country save their own. Benjamin Disraeli
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Probably the reactor coil or control circuits. Shouldn't be too ghard to suss out if you have a schematic and know how to chase a circuit.
It is likely a Squarewave 255. If it has all digital LCD panels and buttons then yeah it is a Squarewave 255. They were a bit ahead of their time. Worked well, but didn't sell well. Most welders still wanted analog dials and rotory knobs. The Squarewave 275 replaced it and went back to dials and knobs.
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On Tue, 12 Oct 2004 05:26:30 GMT, Ernie Leimkuhler

Thanks Ernie. He said it was either a 350 or 400. Ill find out in the next couple days.
Did you happen to follow the Hobart CyberTig 2 thread? Any info about those machines?
Gunner
Liberals - Cosmopolitan critics, men who are the friends of every country save their own. Benjamin Disraeli
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Gunner wrote:

The first thing to check is the POT itself. If he's changed the boards, then there isn't a whole lot else to go wrong. Does it have the LED (or mechanical) meters? Does the current reading change when you turn the dial (without triggering the amp-trol)? If not, and it just keeps reading 400, the pot would be the first thing to change. You can also check it with a DVM. If the current reading does change (when not triggered, the meter reads the max current setting) then there is a blown SCR or something like that in the power section down below.

Well, it sounds like the Square wave TIG 300, same machine I have. Wow, a great welder, too.
Jon
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Jon Elson wrote:

My first thought exactly! I've watched a bunch of expensive boards being changed before someone noticed the pot had gone open. Rather like stripping down an engine before I checked the fuel tank, er .... that wasn't me, ... really.
Fred R
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Jon Elson wrote:

One other thing. There is a pulse switch and current set button for pulse mode. If either switch or button go flakey, it can force the machine to run at the pulse current setting instead of the main current setting. You might just try flipping all the switches about 10 times to clean the contacts. This is a problem noted in the instruction book.
Jon
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