This one's definitely odd. When a Data East/Sega DMD circuit loses 5v it will reset and show "Display Version." At first glance this seems to be what is happening. Yet, the CPU is also non-responsive. Which points to a possible 5v issue at the power supply or wiring harness/connectors, or a CPU logic issue that is sending a reset signal to the DMD, if that's possible.

Was the game working before these issues cropped up?

5.2v is probably fine but a bit higher than I've ever seen an original power supply board put out. That gives me the impression that the 5v rail is probably not loaded down like it should be, as things aren't working.

It definitely sounds like the 6808 CPU is shorted internally, bringing down the 5v supply and causing the display issue. Hopefully that's your smoking gun (no pun intended)!