So by pure luck I managed to get hold of a CPU and ROM board but to no avail.
The seller they had came from a working machine and with them in I have exactly the same results.
So they are put to one side. I have checked all caps now for capacitance and ESR (out of circuit) and I have to say they are all really good.
I have also re-soldered everything including the board connectors in the nests as the machine had been in a pretty grim store cupboard for about
15 years.
For my tests I only have 1 input installed, the ROM, CPU, RAM, Display processor/driver and the Analog display driver.
I am not used to probing digital systems so maybe someone with knowledge might be able to steer me in the right direction.
For those playing along I have taken a few pictures of the ROM, RAM and CPU edge connectors.
The I/O bus all sits at 5V as do the outputs from the decoders. I presume thats because the CPU is stalled. I also do not have pcb extenders which is a real bind.
SO before I buy a signature analyser is there anything else I might have overlooked?