I have a problem with a dark iMac (DV 500MHz) screen, and in my search for a solution I found the following on Apple's support forums:
"Often this problem can be fixed by adjusting the transformer. I don't know if its necessarily correct to do, but I maintain a school full of computers, and have done this very thing many times.
On that computer if you take off the bottom cover (4 screws #2 phillips), on the left side as the monitor faces you, there is a transformer with 2 adjustment knobs on it. (CAUTION!) This transformer produces a charge somewhere in the vicinity of 6000 volts, and doesn't fell good if you get zapped (I've never been zapped as I prefer to be careful). Also on both sides of this are the power supply for the computer, and other components.
Anyway, the two knobs are labeled, "SCREEN" and "FOCUS". A #1 Phillips screwdriver fits into these for easy adjustment. The focus is self explanatory, but the screen adjustment controls the brightness of the screen. Make small movements, and don't close it up until after you've watched if for approximately 15 minutes to be sure you're happy with the setting. Sometimes they'll change after being on for about 15 minutes or so.
If the latter is the case, then the transformer may be on its way out.
If you have trouble seeing where you want to put the screwdriver and the screen at the same time, just lean a mirror if you have one against the wall and watch the video in the mirror as you adjust it.
iMac slot loading"
Does anyone here have experience with this procedure or similar hacks/repairs? and do you have some good advice?