Stuff for tray-loading iMacs
Nothing of interest for slot-loaders here!
Firmware info for tray-loaders
Monitor flyback transformer problem (usual symptom: blank screen, iMac won't start up)
Firmware info for tray-loaders
Note that tray-loaders do not suffer from the same firmware/OS X problem as slot-loaders.
But to install and run OS 9 or OS X on a tray loader you need "firmware 1.2" which you can download from the Apple website: http://docs.info.apple.com/article.html?artnum=60384. In theory you shouldn't be able to install OS 9 or OS X without doing this update.
If you are not sure whether your firmware is up-to-date, you can
3.0.f3, build
date 12/02/98
3.0.f10, build date 03/05/99
3.0.f2, build date 04/23/99 (this is the 1.2 firmware update)
3.0.f3, build date 07/16/99 (if you have this then you are really up-to-date;
no further action required!)
Monitor flyback transformer problem
Although tray-loaders don't suffer from a similar firmware/video/OS X problem to the slot-loaders, they are much more prone to failure of the Flyback Transformer (FBT) on the Power/Analog Video (PAV) board. This is the transformer that steps up the voltage to the 20,000+ volts that the CRT needs.
The complete details on diagnosis of this problem - and repair, if you are so inclined - are on these excellent pages by Zachary Komon http://www.macopz.com/columns/imacrepair (update 2.1.2005: the macopz site is currently down ... here is a mirror of the relevant pages). Diagnosis is easy, but repair is not for the faint-hearted as working around the CRT potentially exposes you to life-threatening voltages, unless you take the necessary precautions.
The problem is caused by overheating of the MFT. The following suggestions have been made to help prevent it from happening: