My Lionel engines stop after passing over one UCS uncoupler. I assume there is some kind of short. Any suggestions on how I can fix this problem?
Check the core of the electromagnet to see whether it is shorted to the base of the track. It should be isolated, with an insulating disk under it, which may be absent or shifted out of place. If this is the problem, you will pretty much have to take the thing completely apart.
Please define “stops”. Is the e-unit shifting to neutral, or does there seem to be no power on the rails beyond a certain point? What may be happening is that there is no power feed to the center rail on that side of the electromagnet. Are all of the pins in place?