Hi Saab,
not that I have ever seen with Intel stuff (the 240V switch on the front died out in the early '90s), but your point is relevant, as you'll see.
I am pleased to say that the fault has been found. Lessee, I had a redundant component for everything - EXCEPT - the power switch on the case! I tested it for continuity, saw none, and repaired it.
The trusty old duallie is running quite nicely now and it's a relief not to lose the 600GB RAID0 drive (which was backed up, but would have been a pain to restore).
Cheers again to everyone who encouraged me not to give up.
BOFH