Toasted my TIG! (help!)

[outofstepper]

Greets all. Long time no post.. but check in every now and again.

Did a brilliant job destroying my TIG while trying to save £300 with a home
brew foot controller.

The machine is a Cemont Arcotech TX160 ac/dc.
Looks a little funny but great little box. Been going strong for almost
10 years now.

Was hoping I could describe what happened and maybe some kind
soul could provide some insight? I realize this kind of stuff is hard
to do.. but any tips welcomed.

Old foot controller: plastic volume control. Worked fine except it
cut off my low and high range. Instead of the full 5-150 the pedal
gave me about 20-130 or so.

Idle hands and all.. decided to make new foot controller. Turned
out nice. Here's a vid:

http://www.youtube.com/watch?v=nzKuQQKcclM&list=HL1338133658&feature=mh_lolz

Anyway, long story short, plugged the pedal in and was tuning in
the range (limits for switch and pot).. when I noticed my pot in
the pedal smoking.

Immediately shut all off .. the pot in the pedal had burned out.

Replaced pot in pedal and came to find that I'd lost all amp control!

Even with no pedal, the machine now won't do anything but maybe
5 amps.

Everything else seems to work.. AC/DC, pulse, freq.. I can strike
arc etc etc.. Its just like the panel pot is stuck low.

I'll continue saga in next post to keep this digestible.

Tony

 

[outofstepper]

Made some calls the only one willing to talk was Paul
at Telford group. Great guy! Said it was likely one of the
top two control boards.. start with top most one as its
cheaper.

This set me back 220 euros (from Italy).

Put it in and no change.

Now the 2nd board will cost me 400 euros. Damn.

This is a hobby.. I don't even know how I managed to
buy this box in the first place. I earn no money with it.

Anyway, I've decided to dig in myself hoping to find something
obvious.

Let me mention the logic board (the 400euro one) looks pristine.
I know you can't tell .. but at least nothing has exploded.

So those are the facts.

Next post is my hypothesis as to what happened.

Stay tuned!
Tony

 

[outofstepper]

Ok so the new foot controller is all metal.
I didn't have the greatest switch in it (DIY!) .. the metal
pedal was on the metal workbench.

I has my torch and ground rigged on the bench so I had
a hands free 1/16" gap and an ammeter on the leads.

I was trying to tune the pot limits in and set the timing on
the on/off switch.

Here's the brilliant part.. I THINK I might've gotten HF/HV
through the case of the foot control and right into my
little tig box!

Here's an artists representation of what I think may have
done the damage:

Tony

 

[langy]

Probably not what you want to hear but its a great case for buying the proper pedal for your machine, Never had a problem with mine.

 

[voipio]

Putting a metal footswitch onto the workbench might not have been the best idea since, on most welders, neither +ve or -ve terminals are grounded, as they have to be able to "float" for the HF start to work in both electrode +ve and -ve modes, meaning the table was probably "buzzed" with quite a few volts by the HF start.

The board to which the footswitch connector leads attach is the one most likely to be affected. The fact you're getting at least some welding current, albeit about 5A, or close to the bottom of the range, suggests that 90% the welder is probably basically working, that's assuming that the other things, like HF start and gas solenoid are operating correctly. It's likely you've either blown a resistor or one of the semiconductors on the board has been "zapped" by the high voltages generated by the HF start system so there's no means for passing the current setting signal to the circuitry that controls the current.

Tracking down the affected component(s) is going to be the tricky bit. A circuit diagram would help. Striking up a dialogue with Cemont might get you some answers although, rather ominously, the "contact us" link on their website doesn't work.

 

[outofstepper]

Thanks guys.
Yeah the Cemont folks aren't very helpful unfortunately. Their stock
answer is to send it to a service center. Fair enough I guess as its
probably a headache to talk to people like me trying to fix themselves
on a budget.

The welder has two "control" boards.. a top board, all analog (cheaper
of the two) is what they told me it would be when I pushed them into
a corner a bit.

As I said it didn't do the trick and there's the 2nd board they call
the "logic board" .. big ticket item (for me). Here's a pic.

Like I said, i'm no tech, but it looks good to me. Meaning I'd expect
HF/HV to have blown something physically.

here's a detail shot of the only two pieces that looked "different" but I
think its just dust/dirt.

i tore deeper into the machine today but everything looks fine.
again I know that doesn't mean anything but at least I didn't find
an obvious culprit.

Yes the machine goes through HF strikes / strikes are / gas works fine..
best as I can tell the whole front panel works though I can't really test
all the pulse/freq settings as they probably disappear at that low current
level.

Same thing on stick welding settings.. I can *just* light an arc and
keep it going if the gap is small.

You guys know which component (in general) would control the current
through this machine? A big transistor? If I can find the component thats
keeping the show from starting I could start tracing back through
the circuit.

Cemont won't give me diagrams.

I can get a used version of this machine for 800-1000 euro. Wonder
if thats the way to go and keep this as a spares box.

Tony

 

[FranV8]

Hmm, I think you're going to struggle with the approach you're taking. Sadly often electronic components (or even the joints on the board) fail with no visual indication whatsoever.

The second board you show is also the one with the more sensitive components on it.

I think your best option is to talk with a service centre. Without the circuit diagrams, or anything obvious blown, you're pretty much in the dark. At least what the service centre can't do, is put a brand new board in, find it still doesn't work and then charge you for it.

Good luck with sorting it out.

 

[voipio]

The fact that replacing the analogue board didn't make a difference would point to the more expensive board being the issue. It probably isn't all digital. The presence of at least eight potentiometers would suggest otherwise. Have you been able to trace the wires back from the control pedal socket on the front panel?

The "dirt" around the 8-pin device might suggest that the device has been re-worked or replaced, and maybe there's a bit of flux residue left around it which has attracted dust. The wire link mid upper left on the board suggests not all of the bugs with this board have been ironed out. There are a lot of surface mount resistors and transistors which will need close examination, ideally with a microscope or magnifying glass, to see if there's any damage, plus the printed circuit tracks.

Even if you don't find anything obvious, it is still possible a zap with high voltage might have damaged a semiconductor in a chip without any obvious signs on the surface of the package. Is there an electronics engineer round your way you could ask to have a look? Making an enquiry at a local college or university possibly? Alternatively, a decent amateur radio equipment supplier might have a repair workshop. 400 Euro for a board like this seems a bit excessive. Enough to put me off buying a Cemont!

 

[dannyp]

HF can kill electonics instantly with no visable sings at all.

i would expect the pedal input to have some sort of protection tho

look for MOV's dioeds acroos the inputs, electrolytic capacitors are vunerable to high volts as well, also there will roably be a voltage regulator for ether 5 or 12 volts that provides the referance votage for the potential devider ( power control circuit ) voltage regs really don't like the voltage on there output exceeding there input voltage tends to result in instant fail

 

[outofstepper]

well I took the day and stripped this thing all the way down.

Blew on it like an old nintendo cartridge and put 'er all back together.

Still doesn't work.

I've got a friend who's an EE I'll have him give the board a once
over. If he doesn't find anything its off to Cemont.

PS checked all the input voltages / regulators; they're doing their
job far as I can tell.

Had a close look under high mag at the logic board.. looks like a 16
year old (no offense!) put it together. Lots of cold solder joints.
I supposed it passed QC and its been welding for 8 years but for 2k euro
I would've expected a little better.

Its a tough call when I can get a new Rtech machine for the same
price as this repair.

Thanks again all for having a look.

Tony

 

[Seano]

Its a tough call when I can get a new Rtech machine for the same price as this repair.

Thanks again all for having a look.

Tony

Tony, IMHO, and your heart of hearts I think you have answered your own question in the last statement, I know it sucks when something has served you so well, and then it suddenly no longer wants to play, but as Ole Blue Eyes said once...Thats Life...

 

[outofstepper]

Found a kind soul with a Cemont Smarty AC/DC box.. essentially
its the same internals (i've learned) just a new (cheaper!) casework.

Tomorrow we'll be swapping logic boards. If thats the problem, and I
can get credit from Cemont for the analog board.. I'm golden.. (still
could've bought the factory pedal.. but i suppose thats semantics now).

On top of that I even got Cemont's blessing.. would hate to have my
bad apple cook his logic board too!

I kindly ask that you all keep me in your prayers.

Additionally, I picked up some ArcZone "AnyTime" ("AnyWhere?") electrodes.
I tend to be a bit skeptical, but they say they're good across the board,
AC/DC, high and low amp. Got some 1/16" and 3/32" ... I'll be sure to
post my results here when and if my box is buzzing again.

Thanks again all!
Tony