Interesting responses, thank you. Some knowledgable folks here. ("There goes one now?" don't get that one)
Anyhoo, I will check the pins first, clean them up if necessary and report back. Funny, my primary TS1000 has been completely trouble free (knocks on wood).
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Fixed now, looks like it was the ROM. Motherboard is a ZX-81 Rev 3, all ICs socketed.Pulled the Mostek ROM, cleaned it, re-inserted. Same as before. Inserted a Sinclair ROM removed from a very beat-up TS1000, all is good now. Incidentally, I wonder if when these machines are assembled at the factory, they are tested using the edge connector. In both "new in box" machines, the edge connectors are a a little used.