The saga continues...I just replaced the old
power supply unit (PSU) and everything is working
so far (2+ hours at full CPU loading) - the PSU
is both quieter (subjectively) and cooler than the previous
one.

http://www.thesandbox.net/arm/aleximac/index2.html

I have some guesses why the first one failed, and
the second one may or may not work.

This iMac is as easy to work on as the old Mac LC
and the 6100. Everything is accessible - just for kicks
I disassembled the midplane assembly (logic board + ports +
CPU + RAM) and got a look-see into the back of the LCD -
Samsung with a serial number that starts with the letters
"APL-" Not a generic part.

Alex