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No Heat (Current) Adjustment on Your SA200. SA250, or Classic Machine?
All these Lincoln machines control the welding current (Heat) with a special rheostat m5090c, and the brush on the end of the wiper will eventually wear off. Normally, when this happens, you'll break a wire. I have troubleshot many a machine by feeling for that broken wire. Works on any brand of machine with a wire round rheosthat.
The rheostat should move smoothly, no bumps or stops. You can check it easily with any ohmmeter. Set it on the 100 ohms range, check across the two outside terminals. It should read about 64 ohms, ±5 %. In the real world, you will have resistance, or it will be open.
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Next, check the resistance between the center terminal (wiper) and either outside terminal. You should go from 0 to approximately 64 ohms. No breaks, nice and smooth up and down.
I know nothing about these rheostats, but they are CHINESE, cheap, and your standard Lincoln OEM know will not fit. By clicking on the image or "Buy Now," you can buy them on your Amazon home page,
If your rheostat is good, make sure your DC exciter is working.
If your rheostat is good, make sure your AC exciter is working.
How to Check your shunt coils.
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