...
I removed the CPU and display boards from the case, and cleaned up the goo left by some foam between the keyboard’s keys.
Wires for providing power added:
GND black
+5v Red
+20VFX brown
+5VFX UNreg (connected to R110 1ohm then to large cap C110 +)
I connected the CPU board to a 5V power supply and checked current consumption (around 1.6A). Nothing got hot, so I checked the CPU clock (worked) and the R/W and address lines. The CPU seems to run.
...
Checked Q103..Q107 (display select line drivers) and there appears to be no data on the bases of those transistors. I replaced a 74145 and after that things got to live:
...
The board reacts to keypresses, and things can be configured
One done, heaps to go..