*sigh* it is a hard one, eh?

I'll try an external display to see what happens. A 20" iMac has an external display output though? The iMac is back with her owner so I can't check right away.

Your thought process is totally correct though. Inverter, backlight, and display. However, I don't have any of those spares so I can't really start swapping the components out until I find the bad one.

I think I'll try to format and install the OS using target disc or an external display and see what happens.

Otherwise, it might be off to Microcenter for a $70 diagnostic. I'll bet they just say it's the logic board though. =/

Thanks for the brain storming!