dead tig welder, help...

[integerspin]

I wondered if any one could help me or make any suggestions, Apart from buy a neat little Inverter or take it to a welding shop .. I am in england and it's a murex welder, I don't imagine any one in the states is familiar with them.
But I guess if you can follow a circuit and understand it you would be able to spot when a problem could occour and make some suggestions..]

My tig died last week, quite unspectacular it was to. It's a Transtig 200 square wave. I was just brazing a tip on something and the welder had run for a matter of 10 seconds or so at 30A DC. I think I came off the pedal, then there appeared to be some hf for a fraction of a second. When I hit the pedal to do another bit there was no hf[I didn't check if there was any current]. The gas valve and slope controls all still worked.

I pulled the top and sides off it and had a nosey round inside it. lots of burned suppression caps, I decided to sort all those out and then check all the volatges and stuff in the electrical parts of the welder. Amazingly only one of the caps didn't work, but I replaced all the ones that looked like they had seen better days.

I have only just put the caps back and I haven't checked all the voltages are what they should be. I did make a few checks I should have before removing anything, I checked and there is voltage from +ve wedling socket to -ve welding socket when you turn it to MMA, on AC and DC. I checked and there is voltage when you check it on TIG aswell, that is when you press the footswitch. . No hf though.
The fault table in the diagram/manual, says check the voltage on the pedal socket, it should be 15V which it used to be, it's now 12.3V, I think there is a note next to this item in the pdf to replace PCB2. I will check further later.
My electronic knowledge is very basic, I can figure out how to make something do something but can't really look at a circuit and see what's going on. I have checked the electrical part of the welder and all the filter caps are in spec, the resistors are all ok and everything seems to be as it should be.

I have had the welder since 1990, it came from an aerospace auction, a local welding saleman picked it up for me and had it checked over by their engineer. He replaced a pot in the foot pedal and said otherwise it was perfect. It always had a problem with remote, the remote would work fine then after a while I would loose current. I should have fixed this but kept putting it off, as far as I could see it had to be the pedal, or the remote switch as the rest of the circuit is the same as the local current control.

The manual/diagrams are at
http://www.integerspin.co.uk/downloads/transtig.pdf

Hope someone can help.

[riley mcmillan]

If you have a water cooled torch, there is a possibility that the cable has separated. Hook up a regular welding stinger and see if you have any current.

[awright]

Wow! A question about a welder accompanied by a manual and schematics! Now that's what I call service.

The topology of your welder looks very familiar. I think it has a family resemblance to one of the welders we had a discussion about on this forum not too long ago. It's too late tonight to study the schematic without falling asleep. Maybe tomorrow.

If you have any voltage measurements on the circuit, this is a good time to pass them on.

Hang in there!

awright

[integerspin]

Hi
I thought including the scematic might be a good idea;-)

I seem to have power/current just seem to be lacking hf. I should turn the gas on and scratch start and see if it does work properly. I have current in ac tig and dc tig, I have checked OC voltages are what they have always been.
I dabbed the tungsten down, and it has current.

I seem to have all the voltages on the schematic. I have 240 volts so the ac voltages are slightly different to the listed voltages, but as you would expect.

I have only checked PCB2 it seems that every voltage is as on the schematic. well close to. The 30V are all 31.x and the 15 are 17.x and so on..

I can't look at a circuit and see how it works.. I spent an hour or so looking for a couple of resistors not marked correctly on the layout diagram. I should have just removed the pcb and traced where they were, which is what I ended up doing.

The coil seems to be switched by the bit of circuit in the middle of PCB2 schematic. Bridge1 has 158Vac on it's inputs with 220DC between the output terminals of the bridge..
Q9 has 218V on the collector, 0 on the base and 0 on th emitter.
Q8 has 32V on the emitter, 32V on the base and 0 on the collector.

But I seem to have 25V on C1 and 220 between C1 and C2.

The coil doesn't have any voltage across it.

That is checked with the machine turned on, set to tig AC, hf on, current set at 40. I did try pressing the fooot pedal nothing seemed to change on the bit of circuit with Q8 and Q9 in.

DC voltages are referenced to the -ve welding terminal.

[mccutter]

Does it have HF points? And did you check them? .010" is a common setting... Good Luck, Mate!

[integerspin]

It doesn't have points, the spark gap is a spark plug with the electrode chopped off.

But I have mended it..

The electrolytic capacitors are all greater than 16 years old. I replaced all the electrlytic caps on both pcbs. I replaced IC1, the output pin to the first transistor in the spark circuit was high all the time. I replaced a diode on PCB2. Now all the voltages are rock steady and when I hit the pedal for the first time I was greeted with the wonderfull crackle of HF, music to my ears..

[codearc]

Thats a great machine the square wave if i remember rightly that isnt HF its something else i remember running the arc up and down my hand without getting a shock from it it would just get hot if i didnt move it about