PC85 - Joining the conversation

[CheshireNoir]

I assume you have removed the BASIC, Wordbee, etc eproms and cleaned their pins and re-seated them.  If not I would be doing that as a priority.

I have. I have also now replaced the connectors between the Base and Core boards, and replaced the socket for IC27 (PAK 5, aka the Menu).
It's still unreliable. I checked the contents of the ROMs and they seemed "sane". I'll compare them to a dump to see if there are major differences.
If there aren't, I suspect it's time to pull out the scope and see if there are noisy traces or the like.

Thanks for the help!

Chesh

EDIT: I just compared the ROMs to PC85 ROMS from "outside sources" and A-E ROMS are identical. I ROM (IC27) seems different but dropping the different version onto a ROM and running it gives me a system that flashes up the menu then crashes.