Mystery solved. The nut holding the potentiometer to the case fell off and the Potentiometer dropped into the control box. Fortunately, I found the nut and washer. Had to drop the control box to fix it - Elroy is up and running!
I also fixed the tailstock on the fourth lathe - it was stuck - the threads were dirty - cleaned it up and put it back together.
I looked over the lathes, checked the belts, checked how the tailstock and spindle match up (all are within 1 mm of perfect alignment), checked locking mechanisms and a few other things. All are in good shape (for now).
If you see/have an issue with any lathe - please post the issue on TALK.