I should also state that the current condition of the unit is as follows - the picture shows how easy it is to get to the logic boards from the bottom - the IO board and Video boards are on the top section.
It seems the Video circuit is running as I get a stable screen with what I assume is a cursor in the top left - now that is static so at least the timer that triggers it blanking is not running. This originates from the TPU and ends on pin 10 of IC201C which is located on the Character Generator Board. So that is where my scope will be looking in a minute...
In other testing I have been able to, with some switch fiddling, get the keyboard to make clicks although nothing appears on the screen so I assume I can put the small analyser on the ASCII bus and see if it makes it there or never leaves the Keyboard - if it does not then again the TPU arbitration onto the ASCII bus will be suspect.
I have not tried injecting characters into the parallel or serial ports yet but, that will be worth a try as well while looking at the ASCII bus - I will modify the Baud rate to something I can generate from a modern machine (it is 600 at the moment) - but, I will scope each of the master clocks first to make sure they are coming out of the character generator board.