Proton CD Display Not Working

[prs1]

I have a Proton AC-300 MkII CD player purchased in 1991 and the 7 segment green LED display is not illuminating.

Similarly the Time, Track, Pause & Repeat single LEDs are not lighting up when the appropriate button is pressed. Otherwise the CD and remote control sensor (which is also on the display board) are functioning perfectly.

The LEDs are all controlled by two CD4052B differential 4-Channel multiplexers and the 5 volt power rail seems to be OK to these ICs. Does anyone have a schematic or block diagram of a Proton or similar CD player with a 7 segment LED display which I can use to fault find.

I would have thought a 7 segment display should be pretty easy to trouble shoot once you understand the how they are controlled logically.

Thanks for your help