1986 Idealarc tig 250 new to me very low power

[A1cnc]

I just picked this machine up for $100. I was told it needs a new switch or something, They really didn't know.

Opened it up and blew it out... I don't think it had EVER been blown out before. Good news is it was just dust not grinding dust.

Set the wires for 220v. It does have pf caps but I temporarily disconnected them for testing.
Tried stick first and no spark at all. Fan works, 110v outlets work and indicator light comes on.

Connected up my air cooled tig torch and my pedal from my square wave tig 175, switched to AC. Hit the pedal and gas flows, contactor closes and I get the cutest little tiny arc with no power. It will arc about 1/8" but no power. It doesn't seem like the pedal is changing the current.I even tried controlling the current with the knob after changing the switch to tig250 and still no joy on current control.

Anyone have any ideas on where to start looking for trouble?

TIA

[A1cnc]

Forgot to mention I set the spark gap to .04" And I cleaned the contacts on the selector switch for the polarity, AC as they were pretty dirty and pitted

[A1cnc]

Dam, I was hoping to get some sort of help.

Does anyone know what readings I should get from the transformers?

I did find both pots (current control, and post flow timer) read open on the ohmmeter. I put a 4.7k ohm resister in place of the current control pot to test but that made no difference with the output.

[jpump5]

I don’t know much about your Idealarc, but two
potentiometers failing seems unusual, or a sign
that something really bad happened. Do they
test open from outside terminal to outside terminal,
and outside to wiper(center)? Do they look or smell
burnt?

[Sparkie1957]

The first thing I would check is if it’s wired at the switch for 460v input. The old Idealarc250 machines were able to use 460v by using H1 and H3 input wires from the power on/off switch. If you desired 230v you used H1 and H2 and isolated H3. A machine wired for 460 that is connected to 230 will have very low power and fan will run slow. Download the manual or look at the wiring schematic on the inside of the machine


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[A1cnc]

It is wired for 220v. I pulled the current control pot off and it read open across the outer 2. Open center to right terminal. On the left to center I get from 0 to~400 ohms as I vary it. It varies up to about a 1/4 turn then it goes open.

No smell of majic smoke or signs of heat

[jpump5]

That sure sounds like a burned out pot. I wonder what happened to it
and what else is damaged. It would be nice if it was only the pots.
Have you found a schematic for it on line or inside the machine?

[ccawgc]

under the narrow panel below the control panel is two pcbs. remove 4 screws and pull panel off. Left one controls the weld current and the right one is the timer pcb.
Control HF on time and other things.
There might be a fuse on the left pcb. This welder is controlled by a saturable reactor.
you will need control current to the reactor before the reactor will let weld current through.
The left pcb takes the current pot signal and uses it to control the reactor.
Reactor connects to the two plates on the rear of the pcb.
send me A Private message if you really get stuck. will need code number and serial number.

[A1cnc]

I checked the fuse on the pcb and it is good.

Is there a way to test to see if there is current getting to the saturable reactor?

[A1cnc]

I did some testing the other day. I found I have ~80v getting to the high,med,low selector but 0v to the polarity selector.

I disconnected the variable pot on the current control and put in a 4.7k resistor to see if that made any difference. It does not.

I did not measure any voltage at the wires for the current control.

[ccawgc]

Voltage will get through the reactor but current will not. soon as current is drawn the voltage will drop. If you have 80 volts to the reactor and 0 past the polarity switch you have a bad switch connection or broken weld circuit wire. you may not have voltage on the current pot unless the weld contactor is closed.
Still need code number to be able to pull up the correct machine diagram.
You will need an ampmeter. either one you place in circuit or a clamp meter.
Current is DC so meter must be able to read DC up to around 15 amps.

[A1cnc]

Here is the code and serial #
Code 8809-CR
Serial # AC 629348

I measured for voltage in the stick mode. Unless I am wrong that would have the weld contactor closed.

Where would I put the ammeter?

Thank you for helping me,
I was away last week

[A1cnc]

I have a multimeter that will measure up to 10A ac or dc. Would that be enough?

[A1cnc]

Thank you for the suggestion that it was either a bad switch connection or a bad wire. Turned out to be a bad switch connection.
When I looked closer at the Current selector switch I could see the center connection looked like it had seen some arcing. I pulled the switch out and dismembered it. Sure enough the center contact was pitted and some sort of silver-ish material had built up on it. The center wasn't making contact. I didn't realize that until I disconnected the lead connected to the switch and checked continuity across the terminals. I filed the contacts smooth and clean. Re-assembled and...
I can weld with it now!
There seems to be a BIG difference in power between high and medium but I think the foot pedal is controlling the amperage. I still have a 4.7K ohm resistor connected where the pot was. In the remote current control that wouldn't affect the pedal current would it?

I will try some more tomorrow to see if the pedal is actually varying the amperage. I was just really excited to actually be able to lay a bead with it

[A1cnc]

With more investigation, Today I found the pot in my pedal is quirky. It will vary smoothly then goes open for a split second and then continues to go up.

I soldered the original pot back in after finding it does work reasonably well. turns out my new to me meter when set to the ohm scale defaults to continuity until you press the select button. I thought the pot was bad but it was operator error with the meter operator.....

After setting the amp control switch to use the knob I do in fact have variable current control. WOO HOO!

Hmm Now I have 3 working welders. The Idealarc tig 250, an airco dipstick 160, and a lincoln square wave 175. Guess I have to fix my foot pedal and see which lincoln to keep now.