Lincoln SP175T wire feed problem

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I have a little-used Lincoln SP-175T. Recently it stopped feeding wire. The gun is hot electrically when I pull the trigger, and I can hear the click of the gas solenoid, and a DC voltage (about 7.7VDC) appears between the wirefeed motor's terminals when I pull the trigger. But the wirefeed motor doesn't turn. I can easily move the driving pinchroller with pliers, so the motor isn't physically jammed.I could just order a new motor for about $140 after shipping. (Is there any cheaper place to get it than weldingsupply.com?) But I'm wondering if there is supposed to be more voltage driving it, e.g. 24V or even 12V. You can't really tell what the circuits do on these welders, not without a whole lot of bench diagnostic work.Anyone know what voltage ought to appear between the wires leading to the wirefeed motor? FYI I measured the voltage the easy way. I stuck pins through the wires and clamped my DVM leads to the pins.metalmagpie
Reply:I figured out the odd DC voltage to the wirefeed motor - duh - that voltage (obviously) varies with the wire speed control knob.Interestingly, after I had forcibly moved the drive roller with pliers and then gone back in and re-pinned the feed motor's wires to test the variable voltage seen, the motor started working. Either it was a bad connection from the wires to the motor, which somehow got reconnected by the slight workings on the wires due to mechanically inserting pins, or there was some grit somewhere jamming the motor and my forcibly moving the roller broke it free. Anyway, now time will tell if it stops working again .. but for now, thanks for looking!metalmagpie
Reply:So after that I put the case back on and prepared to put the welder to work. The first time I pulled the trigger I saw a spark come out of the louvers on the side of the case and no more wire feed. So I'm back in the soup again. It's probably a bad circuit board. Anyone with ideas, please let me know.metalmagpie
Reply:I just wanted to follow up this thread in case someone else runs into this problem. First off, I learned that it is possible to get a board schematic simply by calling Lincoln and asking them to email it. Second, we found that on my welder it was the voltage selection switch that was arcing and giving problems. It turned out that all you have to do is to wiggle the switch handle around until the wire feeds, in any given position. Then it will weld reliably again. The switch part only costs a bit over $30, but the actual replacement looks challenging.metalmagpie
Reply:Originally Posted by metalmagpieI have a little-used Lincoln SP-175T.