Well, I'd better update even though it isn't very exciting so far.
Finally clicked that I have a bally -35 mpu, not a stern -100, but hey, there is not a huge difference, just surprised it never clicked with me (bally has "square" tracks, where the sterns are "organic" and curvy track). Funny how in your face it can be and you still just don't see it
Anyway, she didn't boot. Now that is no real surprise, but still... I found 2 traces I marked down but forgot to repair, so did that. Lets see where we stand right now:
1 - LED jammed on, not even the flicker :(
2 - Reset works fine (needs some 'help' with the PC PSU I'm using as the reset circuit times out quicker than the PSU settles)
3 - CPU is certainly doing "something" - the data and address lines are cycling away, and the VMA is strobing
4 - can see activity on the ROM and RAM busses.
What I do know:
The PIAs and CPU and RAM are fine, a swap with known working parts gives the same symptoms.
My bench rig is fine, the working mpu-100 gives me the 6 flashes (the 7th needs 21v which I CBF setting up - besides if you get 6 you're sweet anyway :))
What I think it is:
It may be the bloody jumpers. Could they be more difficult and weirdly documented?
I may have missed a trace (likely!) - this needs a cool head, which I didn't really have at the time. You need to map out the schematic and probe your way around to make sure everything is connected. To ease the frustration, I moved on to strip the top of the Magic playfield, and rebuild the flippers in the IJ :)
Cheers
Jacob
