Hi Rik,
I am pretty sure it is the CPU, the key had fallen out of the monitor
cable and I accidentally plugged it in backwards, and when I turned it I
almost immediately noticed the smell of magic smoke escaping. The +12V
regulator was wrecked, both the 723 and its pass transistor plus a
couple burned foil traces on the power supply board. I have repaired
the power supply and all the voltages are good now, the clock input to
the CPU is good, however the clock outputs are dead. I also fear for
the ROMs in the machine but I can fix that as I had already designed a
ROM card for option ROMs that I could easily modify for the system ROMs.
Paul.
