If the controls are dead but the display and winker LED work, then at least the VFD, VFD supply and the power PIC on the display board are OK. If the rotary and the push buttons are dead, then either the PIC that scans them is dead or is receiving no power. The 5V power rail comes from the main board, and if it was dead, then the winker LED would go out as well. This could be as a result of a blown fuse on the motherboard. However, the VFD would have died as well since the 60V supply is generated indirectly from the 5V.

So: it is likely that your key scanner PIC is dead and needs replacing - a first in my experience.

Check the voltage on the TP33 test pad, bottom right rear of the display board, relative to GND.