I have an Early 2009, 20-inch iMac. At boot, the video backlight flashes on for less than one second, then goes out. I have video, because I can see it by shining a bright light into the screen. I can put it to sleep, then wake, and the backlight returns for less than a second, and goes out again. Now to the good part - I am following Apple's service manual. It guides me first to the inverter. I replaced the inverter, and there's no change. The backlight comes on for a second, then goes out, leaving only the dim video without any backlight. Apple's service manual leads me on to either the LVDS cable, or - failing that, the LCD panel. I think that the power supply is the issue, as that appears to be where the power for the inverter comes from. The service manual seems to think it would be the logic board. I would try to test for loss of voltage at the power supply, but it's a pretty tricky location to get at with power on, and trying to see if there is video on the LCD, too. Plus, I don't have any circuit diagram to tell me where to even attempt testing for what should be 12 volts (as near as I can tell ) I hate to keep changing parts - as I don't have any, and have to order, then return good parts... And, the iMac belongs to a friend, and I hate to keep delaying the repair, or maybe help him decide that the repair will cost more than the iMac is worth. Any help or encouragement for me would be appreciated.