Once i got the screen working i was presented with rubbish.
I needed to image the ROMs for posterity, and that also revealed that one of the ROMs had lost its mind. Fortunately, the ROMs in the spare Microcomputer card were good.
With this and some messing around with the onboard RAM, i was able to get a myriad of outcomes, some of which included evidence of the power-on monitor starting up.
The sockets are great and despite cleaning i could not the system to start. I changed to the spare Microcomputer card and was excited to get a monitor prompt.
I added an empty RAM card and started adding RAM, checking as i went. There was only one faulty 4116.
I added the rest of the cards one at a time with the same result. I could go no further without a keyboard.