Lincoln Tig 300 problems

I picked up a Lincoln tig 300 square wave machine a couple weeks ago.
Code 9298-ff
The guy claimed that the power couldnt be dialed down to anything less
than about 150 amps. Ive receipts for a number of boards he purchased
in '00 etc etc, with no fix.
So I powered it up today to diagnose what is really going on.
1. It will not dial down to less than about 111 amps,using either the
pedal, or the main amp control pot. The machine has digital display
for volts and amps, and with the main control all the way down, I get
an E11, and turn it a smidge, shows 111, then as the knob is turned,
goes all the way to 375 amps as one would expect
Hooking a stinger up, yes...it really is about 111 amps at low, and
all the way up blew an 80 amp breaker on my sub, so yes, that portion
is accurate.
There is no Hi/Low range switch on the machine.
No output on AC. Tiny spark, but no real welding current, using local,
or remote with a known good pedal. Pedal does kick the contactor, and
does vari welding current, but wont bring it down below that 111
volts.
No HF in any configuration. This COULD be dirty points, as its not
been used for at least 8 yrs, but thats not a big issue at the moment.
First thing Ill do is check the main amps control pot, to make sure
its in spec and both sides have the prope variable resistance.
I do have the schematics and drawings, but was looking for some input
on how things actually work..IE..when the main amp knob is turned, how
is it actually controlling the output of the transformer?
With a minimum current of 111 amps, something is not going low enough,
or high enough to vari current to lower values.
Why would it not have output on AC but does on DC? Thats a bit
odd....
Ill clean the AC/DC+/DC- selector switch of course.
It IS a square wave machine, so whatever converts the AC sine to
square wave sine may be an issue. I think thats some sort of chopper
circuit?
Anyone have any ideas or where to start looking? This is a weird one.
The FF designation at the end of the code number means "full
function"..whatever the hell that means. I assume its the timer
circuits for post and pre flow, crater, spot etc ?
Gunner
Political Correctness is a doctrine fostered by a delusional,
illogical liberal minority, and rabidly promoted by an
unscrupulous mainstream media, which holds forth the
proposition that it is entirely possible to pick up a turd by the clean end.
Reply to
Gunner Asch
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Gunner Asch wrote in news: snipped-for-privacy@4ax.com:
Dunno if it'll help but here's a URL for the Owner's Manual:
Reply to
RAM³
BTW, I just sent an e-mail to your de-munged addy.
If it didn't get there, send one to this one [with the ".nospam" removed] and I'll re-send it.
Reply to
RAM³
I have one of these, and the Lincoln machine schematic, which is all they will give out to the general public. The current controls are potentiometers. I wonder if a wire has got a bad connection, leaving one end of the pot disconnected. Maybe you could read the voltage across the current set pot and I can compare it to my machine.
Hmm,
First, when the pedal is up, the display is just reading the setting off the knob. So, the knob provides an adjustable voltage, and the Amps dial reads that voltage with pedal up, and the current coltroller tries to match that voltage with output current when the pedal is down.
The actual welding output is controlled by the phase angle of firing of an SCR bridge. But, if the dial reading is wrong with pedal up, then this problem sounds much less serious.
That is a puzzle, and may indicate more trouble.
No, it just fiddles with the SCR timing to control the current.
Yes. There are machines without many of those functions and no gauges.
Anyway, I had to replace a Tantalum capacitor in the post-flow timer. Otherwise, I haven't had any problem with the machine.
Jon
Reply to
Jon Elson
I would obviously check the pot with a ohmmeter, but I think that this welder has big problems (as in bad boards). If both a pedal and panel pot give the same problem, the issue is in what reads the inputs, most likely. Too many things are wrong at the same time. It should be an interesting project, don't expect a quick answer and go slowly and methodically.
i
Reply to
Ignoramus30765
Looks like you are getting some help - I saw on the pdf - Don't switch the switches with the power on.
Wanta make a bet ? What is the temptation - not right switch to it...zap.
Since board after board wasn't a fix - it might be a switch or pot. Might be cables to /from them. Or any component, Rectifier or relay mounted off the board...
Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member.
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Reply to
Martin H. Eastburn
I think it would be worth looking for a shorted SCR. They are not on a board, so it doesn't sound like they got swapped by the previous owner. It ought to show up poking around with an Ohmeter and the power off. I looked at the PDF of the owners manual and did not see a schematic of the machine. Can you post a pointer to the schematic?
Good Luck, BobH
Reply to
BobH
Yeah, and you already know what the first step is, call that guy you mentioned a while back at Arco Welder Repair. Two sentences, and he'll say "STOP - Check this..." But they've let their domain name lapse, there's a "Domain Available" NetSol squatter page up now.
I'd have to agree with the majority - the former owner has already tried swapping boards, so odds are it's not a board. Bad power SCR or Triac in the output sections, bad potentiometer or cabling in the controls, bad safety switch, open coupling capacitor, bad opto-isolator, etc.
Do a methodical search and you'll find it.
That, and/or make like Jimmy Durante and follow your schnoz - if a component has met an electrically violent end, the nose knows. Stuff your proboscis in there and take a deep sniff, and track down the crispy critter.
(Note: Offer not valid if there are selenium rectifiers or other components that make particularly nasty IDLH fumes when the Magic Smoke escapes. But those are getting few and far between.)
-->--
Reply to
Bruce L. Bergman
]
Thats what Im going to check tommorow. Oddly enough..it works fine in AC stick mode.
The moment I put it to Tig, or DC stick, its full bore balls to the wall. What the manual calls Stick Blast.
After posting the previous and reading some posts, I reread the manual went back out and set everything to stick default, removed the pedal and got it to work on AC stick normally.
But any DC mode and its 300 amps even though the amp meter reads 111
Its very possible it is the current pot.
The schematics that came with it give actual resistance values of components so Ill start with the Current pot and wiring
Gunner
Political Correctness is a doctrine fostered by a delusional, illogical liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.
Reply to
Gunner Asch
Dennis sold Arco to one of his employees I think..he sold to someone and retired in August. So that option is out, the new guy is not the type to give out free info.
What would the SRCs look like in that size? It works ok on AC, its when I switch to DC that its full bore.
I will indeed. It was sweet welding with AC and 6011. Nearly as good as the Dialarc 250
Its later than 1989, so there shouldnt be any seleniums.
Political Correctness is a doctrine fostered by a delusional, illogical liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.
Reply to
Gunner Asch
The welder came wit a file folder full of schamtics and receipts for boards. The schmatics hve values for the various components, so Ill have some data.
Gunner
Political Correctness is a doctrine fostered by a delusional, illogical liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.
Reply to
Gunner Asch
A big metal can or more likely a big plastic and metal block, with two very heavy leads plus one or two much thinner leads (or screws), in either case bolted to a big heatsink.
The SCRs are in the Rectifier assembly on page 38 of (pdf provided by another poster).
A shorted SCR will have low resistance regardless of polarity. Likewise a shorted rectifier.
Joe Gwinn
Reply to
Joseph Gwinn
Oh, this is different than what you originally described. Well, if the current control is OK on stick mode, then most of the really expensive stuff must be OK.
The first thing I'd do is flip every panel toggle switch 20 times to clean up the contacts. See if that helps at all. I'm pretty sure there are microswitches or something similar that tells the electronics where the AC/DC polarity handle is set, they may need exercising, too.
This sounds like two different symptoms, at least. The current meter doesn't read right at the low end, and the current control isn't working right in TIG mode. Of course, there really is little difference between the TIG and stick modes except open-circuit voltage. There are a bunch of Molex connectors on the boards. I have had a lot of trouble with this connector type in rough environments. My machine is in the basement, but if yours is in the garage or whatever, I'd definitely pull and reseat every one of those connectors on the PC boards behind the control panel. It just hinges down for easy access. That may well fix the problem.
Jon
Reply to
Jon Elson
The SCR's are huge, the size of a white hockey puck, clamped between big heat sinks. They are on the output side of the main transformer, deep in the interior of the machine. There are two SCRs and two diodes in a bridge. They are used in all modes of the machine, I believe, to control current in both directions. So, the bridge is just a controllable switch in series between the transformer and electrode. Therefore, since AC current IS controllable, I really don't think the SCRs could be bad. In fact, most of the control systems have to be working for it to get this far. Since boards were replaced, a bad switch or connection seems more likely.
Jon
Reply to
Jon Elson
[ ... ]
Well ... resistors and perhaps caps (depending on the type) will show up -- including pots.
But SCRs and the like tend to fail in such a way that the smoke does not really escape, but is rather trapped where it does no good -- and gives no clues to the nose. (Though it may cook the insulation off the wiring, which you can smell. (If the wiring has Teflon insulation, you better hope that you *don't* smell it cooking. :-)
And I have seen high voltage silicone insulation get the wire zapped from inside it without opening at all -- the insulation just turns limp in certain areas. Not too sure how many welders would be using that insulation -- it was rather uncommon and expensive when I was using it at work -- and we were normally routing 45KV with it, a bit beyond what you would see in the typical welder. :-)
Enjoy, DoN.
Reply to
DoN. Nichols
Molex type connectors do have a service life. The services life is governed by how many times they have been removed and reseated. These connectors are designed with a contact patch (normally tin coated) that will wear away to base metal, base metal will corrode and then the connectors start to create high resistance, thus burning out the connector or solid state part on the board. If I recall correctly, most connectors had a 30 or 40 time reset life. Not much of a life span, if they are reseated a lot... Just my two cents worth about molex type connectors, Of course, I have no idea what's really wrong with Gunners machine!!!!!!!! So I cant help there!!!!!!
bob in phx
Reply to
Bob in Phx
Gunner.... looks like you're getting some good information, but I feel it is my moral responsibility to let you know that your efforts will be futile, and your only recourse is to crate that thing up and send it to me so I can "dispose" of it properly..... Ken.
Reply to
Ken Sterling
That stubby little critter is HEAVY. I used the forklift to put it up on my welding table and tried to shove it into a corner so I could work on it.
I pushed..and it didnt move. I pushed harder and it moved a smidge..puckered up the old bung hole and pushed HARD to get it where i wanted it
Pretty good sized transformer in that critter.
Gunner
Reply to
Gunner
Warning! Stick it on a pallet, and it weighs 840 Lbs. (That actually includes the wheeled cart and a torch cooler.) At least that's what mine weighed when shipped. Fortunately, mine came in excellent shape, and I only had one problem with it, the post-flow timer would stick on. One replacement capacitor and it works like a charm. Bad news is that the thing is full of Tantalum capacitors, which tend to degrade over time, especially if the unit is unused for a couple years.
But, I sure wouldn't even want to pay the shipping on one of these if it has serious problems. It has a very complicated electronic control system that could be real trouble to fix without factory repair documents. Lincoln will send out the machine wiring drawing (I think you can download it from their web site for old models, too) but won't provide info on what is in the boards themselves. The main board must have 40 CMOS 4000 series chips, and there are 3 or 4 smaller boards, too. Even with complete schematics it could take sume serious study to figure out what's wrong.
Jon
Reply to
Jon Elson

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