I had a similar problem with my Jules Jurgensen Optcom 1. When I opened the case, I noticed the screw on the opposite side of the module from the "winder" was missing. By pushing the crown in, the module lifted up along the far edge and made contact with the case, which blanked the display.
If and when you open the case, check the display is sitting tightly in the plastic frame, and also try to insulate the inside of the case with a square of tape.