In this area, we're looking at the SUBOR hardware and trying to understand how the keyboard works.  To begin with, here are some pictures of the insides.  If you are good with hardware, you can help the effort!

Overview

Cartridge in Slot

SUBOR with the cover off

Board Interconnect

Mainboard Interconnect signals

Peripheral Board Interconnect Signals

Mainboard Interconnect Signals

Mainboard Interconnect Signals

Peripheral Board Interconnect Signals