repair of TIG inverter - a bit of advice needed.

[Stephen Giles]

Hello everyone, i'm hoping for a bit of advice to point me in the right direction. Practical help would be even better!

I'm wanting to learn to TIG as a hobby, happy with the length of time that it will probably take me to be even basically competent. I can MIG and gas weld already to a competent / basic level.

I just purchased a 2nd hand TIG (Chinese style AC / DC inverter), got a demo of it, did some TIGing myself. different currents and settings all worked fine. Spent an hour or so, so couldn't have done much more as a test.

Got it home and now the unit fails. Powers up, HF ignition, welds for a few secs then total power loss (fans, display, all but the main power switch goes off, which is an inlne neon). Does the same if i don't weld just leave the unit turned on. If i leave it off, it's ok again after 20 mins or so, but follows the same pattern once on. So strongly suspect the main PSU.

I'm a clearly disappointed, but don't know if it's worth getting repaired - throwing good money after bad luck, repairing myself (i have some electronics gear and skills, but no SMPS experience), or just write it off as really bad luck.

Any thoughts greatly appreciated.

Thanks,

Stephen.

 

[Gareth0123]

I have a dead LTD CT416 combined 3-in-1 ARC/PLASMA/TIG, and I only ever used the plasma until it died on me.......... I have never even opened the clear poly bags the tig and arc bits came in. I am contemplating sending it to these guys for repair; Plasma Parts as they are advertising an all in, back to a new working condition for a fixed price including return delivery, parts, labour and VAT, of only £99.95. Although I know my way around automotive/agricultural/construction equipment electrics I have very little electronics experience.

If I do get around to having it repaired it will only be to practice my TIG techniques as I have not tig welded in about 20 years. If I get on with the tig and there is a demand for it within my business, then I will sell on this repaired 3-in-1 machine along with about £100 worth of plasma consumables I have for it, to help provide funds for a dedicated tig set for my workshop.

 

[Cobbler]

I know nothing about TIGs, but from your description, if it all goes off including the fan, it sounds to me if there is a thermal overload or main switch or similar that's gone faulty. If it was the electronics, the fan would continue to run as the feed from this would be straight from the input after the switch. I would think this would be fairly easy to find, BUT BEWARE there is HF current & voltage in there

EDIT by the way Stephen welcome to the forum

 

[Bill Edwards]

If you've got what it takes to open it up, dab around with a meter (safely) and tinker then you might be able to find out what is wrong and fix it with the only real cost being your time.
If you need to pay somebody else to do it then the question would be what is it/what is it worth?
A £150 cheap job isn't worth much, if it's an £800 decent make then that changes things!

 

[Stephen Giles]

the 2nd hand machine was £180 as i bought it. With an OK torch, + foot pedal.
http://www.stamos-welding.com/s-ac200p-basic

so it's half way between your 2 price sets.... as new, but didn't cost me a huge amount. - but i've also now got a full bottle of argon, which wasn't cheap!

I've had the case off and started mapping the start and safety circuits last night. I've worked on some switch modes before (with little success in fixing), so i'll be careful and check / discharge caps as i go.
The build quality is ok in some areas and pretty poor in others. Just hope the issues isn't in the middle of the switch mode as it gets beyond my electronics skills.

I'll check out where the fans hook up and how the unit black starts / deals with large currents / protection system and see if i can see anything in that puts it into shutdown at the start of the high side.

Thanks for the thoughts so far...

Stephen.

 

[skotl]

Welcome, Stephen.

Have you been back to the seller? While legally you don't have any comeback I've certainly heard of guilt-ridden sellers who will reimburse some or all of the money if the unit ends up bust.

PM me if you want a hand / second pair of eyes on the unit - I'm in Dalmeny.

Cheers
Scott

 

[Stephen Giles]

I have been back to the seller, who seemed surprised that it didn't work. I did test it for about an hour before buying it. It welded fine on AC and DC at a range of currents and never turned off at all during that hour. I can only assume it was the move of the machine in my car + sitting in my garage (cold!) for 2 days before i tried it in anger.

thanks for the offer, might take you up on that. At the very least, (if i get it working) i could do with some novice TIG starting pointers.

Thanks,

Stephen.

 

[skotl]

I have been back to the seller, who seemed surprised that it didn't work. I did test it for about an hour before buying it. It welded fine on AC and DC at a range of currents and never turned off at all during that hour. I can only assume it was the move of the machine in my car + sitting in my garage (cold!) for 2 days before i tried it in anger.

thanks for the offer, might take you up on that. At the very least, (if i get it working) i could do with some novice TIG starting pointers.

Thanks,

Stephen.

I'm happy to look inside the machine, but I've never done TIG welding so won't be any good once it starts working

 

[HMB]

BUT BEWARE there is HF current & voltage in there

Mmmm currents.....

 

[Stephen Giles]

i manged to, i hope(!) repair the TIG. turned out to be a failing zener in a protection circuit, which was kicking in and shutting down the welder.

The welder runs now and i have even done a very very bad bead or 2.

do people like 2T with foot pedal, or 4t better?
4t seems like it provides a bit more control when starting, then less to do when welding.

thanks to all those who replied.

Stephen.

 

[skotl]

Good work