Had a perfectly running 2-4-4-2 on a simple figure 8 layout.  Would occasionally switch-out loco & rolling stock.  Mysteriously, the loco stopped moving though the lights & sound would work perfectly.  Indication of short on controller.  Did my best to clean base of loco & trucks with gentle brushing and blowing but no help.  Other locos work fine on track.  Not getting indication of short anymore but still having problem.

Any ideas?  I don't really know what I'm doing, just doing my best.

Thanks,
Art