Just a quick update.
I'm starting to get into the board testing now that I have managed to clear some space in the garage to lay everything out.
Currently the board isn't even booting or performing any diagnostic tests, it just sits with solid red LEDs all the time. I'm learning how to use my Oscilloscope properly so that is fun, also I'm having fun testing with the logic probe that I bought. The combination of these two and a decent multi Meter is making it much easier to follow the guidance I am getting over at KLOV to test the various chips and circuits.
So far we have reduced the first problem area to that of the watchdogging and reset circuits that are keeping the game board in a permanent state of reset, which would explain why it never boots or performs any diagnostics.
Pretty fascinating stuff to walk through when you are being guided by someone who knows, otherwise it would be pure hell for sure.
If you're interested in all the nitty gritty hi, lo, mhz, clocks and pin-outs gobbledeegook then you can follow along with the dedicated board repair thread
here