OK I've narrowed down the loud POP I heard (followed by an immediate shutdown) to the display hardware, but I can't see any obvious blown components.
The current state is this: the machine works fine, but the display has big green and magenta blobs on the left 3rd of the screen and it's a little bit shrunk on that side too. I suspect this is due to overheating after I did the quiet fan mod (Zalman variable resistor thingy), it was working perfectly well for several days, powered off at night. Right now I have my eMac completely apart, the display board is out and I'm suspecting the transistors on the heat sinks but there are so many of them, and I can't see any that are obviously blown; I'm hoping someone here will know which one is the likely culprit, how I can test it (I have a decent digital multimeter) and where the best place in the UK might be to get replacement components. I'll be damned if I'm scrapping this off if it's just one component that I can change myself!
It's a 1GHz eMac by the way, which I have modded to 1.33GHz (though I really don't think that has anything to do with this fault other than possibly causing the display hardware to overheat, combined with the slow fan mod)
If there's no cure for the display, some kind of VGA port mod and recasing the guts sounds intriguing... has anyone pulled this off? It would be rather nice to run it on a 22" monitor! I suspect the original eMac tube is still good too though, so the machine may be worth more as parts than to get repaired by Apple.