Tom,
Is the F/O/R switch a DPDT (for just switching the polarity to the DC motor) or are there additional poles on that switch? Some of the mini lathes have an additional? pole on the F/O/R switch that connects the controller board's P1 to P4 connections for reverse. Some have P1 and P4 hard wired, so there would be 2 wires going to P1, one to P4 and the other being a wire to the pot. If you removed the pot for cleaning and disconnected the wires to P1,P2,P3, there is a chance that a connection became open during the whole process.
Pictures of the wiring would be helpful.
Regards,
Gary
