CPU Board
Board overview:
Schematics:
Actual CPU part
Smaller subschemas
Display
The front panel looks as follows:
The display board layout:
It is actual 2 boards; the middle keyboard is a separate one connected by a dip flat cable.
Its schematic diagram:
And part 2:
Initial state
I removed the CPU and display boards from the case, and cleaned up the goo left by some foam between the keyboard’s keys.
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.
After that I connected CPU board and display board together and powered them up with 5V and got display:
and after that lamp test like display:
The initial display seems to be a lamp test, and from that we can see that some displays do not work: the three alphanumeric ones on the left and the two on the right. The “channel” one initially did not work either but that was just a loose connection.
Focusing on the “unit” display I checked U4, a shift register for one of the digits (74ls164). pin 8 is its clock (blue) and pin 1 is its data (yellow):
So we do seem to have data being shifted through.
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