Thanks for the replies, guys.
I removed the tubes and powered it up. It took a couple of minutes, and then the display had an 'e.' value and all the odd numbered LEDs were illuminated (1,3,5, etc. plus Edit)
After a couple of minutes, the display and all the LEDs flashed randomly for about two minutes (the Clip LEDs did not). Then all the lights went out. The transformer had a regular (and normal) hum throughout.
I waited about 5 minutes but there was no more activity. I powered the unit down, waited a minute, and restarted it. This time there was no activity at all, so I shut it down after about 5 min.
The ribbon cable looks ok - there are no cuts and the socket is seated squarely on the board. The EPROM is secure as well. Is there anything else I can check/reset, or do I need to find someone with a meter?
Thanks,
Willem