You know the iMac Firmware and Jag issue, right? [See this hint - editor.] I just discovered, and perhaps I'm not the first but I do feel a bit like Columbus, how to get enough video back on the iMac to upgrade the firmware without doing Apple's hokie pokie with FireWire targets and ANA or having to take it to a repair Shop.
The other day I was trying to clear the firmware on an XServe to clear the Open Firmware password. I did this by adding memory and then clearing the PRAM three times. I decided to try it out of desperation on this dead iMac, mostly because this iMac slot loader didn't have FireWire to target my TiG4. After adding RAM, I started the computer, cleared PRAM three times and, "BAM!", an ugly blue screen appeared and then the iMac proceeded to boot into OS 9. You may be able to do this by removing RAM and clearing PRAM three times as well, instead of adding it.
I had to upgrade the OS to 9.2.1 to put the firmware on, and I did it all on this ugly blue screen and "BAM!" after it's success, I succesfully upgraded the firmware! This is the only computer I have tried this fix on; I would love to hear others try it and hopefully their success stories.
[Editor's note: If you've got firmware issues, this might be worth a shot before resorting to the repair shops...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2003011108553231