Using Sys7 CPU/Driver in Sys3
First, if this has been covered comprehensively somewhere, please let me know. I have been able to find chunks of support documentation in several different places and I am having trouble matching up all the details of what I need to do.
I suppose getting the S7 cpu board to boot would be a good first step. The board has Leon's test ROM in IC-17. I understood this can be done without any jumper changes, just that W-11 is installed, which it is, and W-12 is out, which it is.
I also have a jumper from C23 (+ side) to the bottom of R3 in lieu of connecting +12VDC. This is in some dispute as one resource says to jumper C23 + to R27 which is connected directly to ground. Hopefully R3 is correct.
With the above conditions, I have a clip lead from the +5VDC on the power supply to TP9. Ground is supplied via clip lead from "-" side of C13 on PS to TP10 on CPU.
I have a probe clipped to ground to tap IC1.40 to RESET.
Upon connecting power and RESETing IC 1, I get both LEDs lit solidly and a zero in the diag display. They never change state, although at times the segment display would flicker segments that resembled an "8". I understood this to mean the board was "locked up".
I put the logic probe to work. IC1, 6808 has two DATA lines stuck LO, D5 and D4 at pins 28 & 29 resp. Swapping in a 6802 resulted in same condition. 6808 back in. If I lift those two pins out of the socket and reinsert the chip, those two pins "float" with no connection.
Put those pins back. They are tied directly to IC9, which then outputs the signals to the DATA BUSS. Replaced IC9 with socket, but unfortunately the same result. If I remove IC9 from the socket, all outputs from IC1 going to IC9 go no connection. D5 and D4 still stuck LO.
It is my understanding that D5 and D4 should be pulsing everywhere on the board with that designation. They are all LO. None of them have continuity beeps to the ground plane.
I do not want to replace any more unnecessary components.