My TIG welder is playing up...

[Munkul]

I have a lovely old ESAB DTM 250 Aristotig. It has a built in water cooler, does AC/DC, does 200 amps @ 100%, and has plenty adjustment to play with. I have (or had?) no intention of upgrading it to anything newer.

It's dated as 1991 (IIRC) and is an inverter driven unit.

anyways, it welds on DC just fine. Sometimes the HF seems a bit weak, but always works.

on AC i've never had a problem with it, but I don't do all that much aluminium... anyways the last few days I've been making some alloy ramps from 1/4" treadplate, and running long seams around 180-200amps.

About half an hour into welding, it starts playing up.... EITHER:

- it doesn't light up an arc, it just shoots large HF-like sparks at the workpiece
or - it extinguishes the arc mid-weld, and again just shoots HF sparks
or - the arc goes very weird - changes sound, must drop the current massively, and in general acts unstably. This only lasts a little time before it just extinguishes like above.

If I play with the frequency knob, I can generally get it to work again fairly easily, for a while at least. It doesn't seem related to overheating, because it used to do this sometimes if it hadn't been used for a while (I put it down to sitting in a cold garage) and also if I leave it to cool down, it doesn't make any difference.

I've had the panels off and all the boards look fine.

I've tried changing tungstens, collets, gas flow, even changed the gas bottle itself in an effort to see if it's not the machine itself...

These sparks, they are much bigger and stronger than the usual HF sparks this machine puts out.

Anyone any ideas?

[shovelon]

Have you checked your HF point gaps? An improper gap could hamper arc start and AC stability. Also loose screws or wires. Another thing from experience is remove your ground cable from the clamp and connector on the machine and reset. On occasion I have had the copper commit suicide in those locations and affect continuity.

When was the last time you changed your coolant?

[Munkul]

I haven't checked the HF points yet, in fact I have never even seen a set of HF points but I'm reasonably competent with electrickery so I should be able to work it out. Reading the ESAB service manual it leads me to believe the HF is used for ignition and arc stability, and on AC the HF sends current from both polarities for stability. Could be related to my problem.

The ground clamp is good... from outside the machine, anyway. I've tried two leads already. I haven't dismantled the torch connectors/adapters yet, though.

Coolant? erm... about 6-7 years ago? the torch still stays cool... is that not good enough?

[albrightree]

Foot pedals often go bad, but are easy to check with multi-meter. Hope it isn't a board, thats an older unit. I had something similar happen on my airco(esab) squarewave 250 and had to have the PC board repaired. About a year after repairing circuit board I had something similar happen, and found a bad pot on foot pedal. When you check foot pedal, jiggle the cable when checking for continuity,and resistance, cables and connectors can go bad after a couple of decades of use too.
Good luck, hope you solve it, sounds like a nice machine.

[albrightree]

Is this the machine?

Looked at manual : http://pdfmanuals.esab.com/private/L...20096%20GB.pdf

Manual doesn't show HF points/gap in maintenance section of manual. Has a "Hot Start" feature ? It might do the HF electronically ?

I didn't know they made stuff like this in the early 1990's. Pretty high tech for back then.

[Munkul]

That's the machine. I have that operator's manual, and I also have the service manual, which goes into much greater depth.

It makes no reference to cleaning or setting points, which makes me think it's all done electronically, and the testing diagram just shows connecting the unit output to a spark plug to test it.

I don't have a foot pedal for it (i wish i did!) just a torch button. The service manual explains the panel controls (frequency, balance, slope up, down and current) are all just 10k potentiometers wired to give 0-10v input to the control boards. Knowing this, gives me a fighting chance of fixing it if it's something simple like a dodgy pot.

Honestly, it's a brilliant welder, must have been bleeding edge technology when it came out. The 2T function is configured in such a way that I can use the down and up slopes to control my amps at the end of a run by letting off and tapping the button. Makes it so i don't particularly NEED a foot pedal for aluminium.

[Munkul]

well I think I worked out what it was.... It quit working altogether the other night, and co-incidentally we'd just had a fast thaw and there was dripping condensation on EVERYTHING.... so I took the sides off, and left it in front of the workshop heater for half a day.... guess what, it now works perfectly again... I did about 4m of AC weld around 160-200amps and not a single hiccup.

Guess I need to keep my welders warmer and drier

I confirmed the HF box is a sealed electronic unit. I don't think I can do anything with it... but the HF actually seems much stronger on DC than it did before. I guess moisture was draining HF somewhere.

[albrightree]

Glad to hear it was something simple. I have the same problem in my unheated garage. Electronics dont like too much humidity.Luckily most welder PC board appear to have been coated. If they weren't they probably wouldn't last very long. Lost several pounds of wire, and welding rod from suddenly warm weather that happens all too frequently(water dripping off of everything). I try to keep the welder, drill press, and tool box covered as much as possible. I would love to have heat in there, but it could be a little expensive. Good luck, and you might have to keep the welder in the house where its dry.https://www.weldingweb.com/images/smilies/laughing.gif

[sapperb]

well I think I worked out what it was.... It quit working altogether the other night, and co-incidentally we'd just had a fast thaw and there was dripping condensation on EVERYTHING.... so I took the sides off, and left it in front of the workshop heater for half a day.... guess what, it now works perfectly again... I did about 4m of AC weld around 160-200amps and not a single hiccup.

Guess I need to keep my welders warmer and drier

I confirmed the HF box is a sealed electronic unit. I don't think I can do anything with it... but the HF actually seems much stronger on DC than it did before. I guess moisture was draining HF somewhere.

Good to hear. I cover mine with Big BBQ covers...They fit, especially with the bottle on the back. I live in the High Dezert (Cali) and the sand and dust get everywhere. Have to protect your investments brah...

[Munkul]

so I had another problem at the weekend... moved it around, plugged in earth clamp, tried to light up... no joy. HF was working but just didnt seem to do anything to my workpiece.

...Put it in front of the heater for an hour. Tried again, still no joy.

...5 mins of cursing later, i realised that I'd plugged the earth clamp to the -ve plug and not the +ve


how many years have I owned and used this machine and I'me still getting it wrong?