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Thread: 1986 Idealarc tig 250 new to me very low power

  1. #1
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    1986 Idealarc tig 250 new to me very low power

    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

  2. #2
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    Re: 1986 Idealarc tig 250 new to me very low power

    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

  3. #3
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    Re: 1986 Idealarc tig 250 new to me very low power

    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.

  4. #4
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    Re: 1986 Idealarc tig 250 new to me very low power

    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?
    Miller a/c-d/c Thunderbolt XL
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  5. #5
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    Re: 1986 Idealarc tig 250 new to me very low power

    The first thing I would check is if itís 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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    Miller Dialarc 250 (1990)
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  7. #6
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    Re: 1986 Idealarc tig 250 new to me very low power

    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

  8. #7
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    Re: 1986 Idealarc tig 250 new to me very low power

    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?
    Miller a/c-d/c Thunderbolt XL
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  9. #8
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    Re: 1986 Idealarc tig 250 new to me very low power

    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.

  10. #9
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    Re: 1986 Idealarc tig 250 new to me very low power

    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?

  11. #10
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    Re: 1986 Idealarc tig 250 new to me very low power

    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.

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