I have a miller econotig from 1995. As soon as you touch the pedal, it’s full amperage. No control at all with foot pedal. Tested foot pedal, and getting 1k ohms released, and 1 ohm fully pressed down. And it moves smoothly through the range. Replaced sup1 and sup2, still does the same exact thing. Disconnect rc4 or rc5 and it welds at the minimum amperage. No idea where to go from here
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Originally posted by Franz© View PostCheck the panel/remote switch and verify the switch is functioning as it should.
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Originally posted by jjohn76 View PostDid you replace SUP1 and SUP2 because the board showed short circuit across RC4 and RC5 without the shunt winding connected?
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Ok, since it's open loop, your shunt drive SCR (Q13) is probably still good. It looks like optocoupler OC2 should also be ok, or you would see some resistance across RC4 and RC5. What resistance do you measure from RC9-4 to board ground (checks if Q12 is ok)?
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Another possibility is C35 could be shorting out at voltages higher than your multimeter uses to measure resistance. Either way, it seems either your shunt driver circuit is shorting out without being triggered, or your trigger circuit is turning on Q13 (shunt SCR) all the time.
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Originally posted by jjohn76 View PostOk, since it's open loop, your shunt drive SCR (Q13) is probably still good. It looks like optocoupler OC2 should also be ok, or you would see some resistance across RC4 and RC5. What resistance do you measure from RC9-4 to board ground (checks if Q12 is ok)?
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