Chosen Solution
I’m debating on whether this is a dead LCD display or a bad video controller. Since the external display work (VGA adapter to Dell 19"). System Profile does not detect any displays connected, though the external connection does work. I’ve found the video adapter 661-4673 for about $190, and this is definitely the cheaper of the 2 components. A replacement LCD is about 3x that. :( I checked the graphics ROM version and it matches the newer version mentioned in the Apple support doc DL71 Any suggestions on diagnosing this further? This had been running 10.5 and I’m in the process of upgrading to 10.6.
If the GPU/video controller was defective you would have no external video so I doubt replacing the video controller would fix things here. You likely have either a CFL issue or the inverter has gone. Whats odd here is Profile doesn’t show your display. Are you sure you were looking under the right heading Graphics/Displays Click on the heading and it should show info for both displays iMac and External. Have you tried running Apple Hardware Test? Looking at your display at an angle you should see a faint image of your desktop (with laptops you can often use a flashlight to shine through the Apple logo here you can’t). If you can then you have video only the lighting of the display has a problem.
I serviced dead backlight issue last week, more on that here: http://forums.macrumors.com/showthread.p… there are three types of voltages going in the inverter- 24V DC main voltage, backlight ON/OFF signal (I refer that as backlight-enable in the post on macrumors forum) that should be 2-5.5V DC to get the backlight, and Backglight-intensity voltage (on the inverter pcb marked as VBR) that should be between 0-3.3V DC. check these and tell us your measurements to trace down the problem.
I have the same issue No Display on iMac LCD , but it`s working fine on external Monitor. Already I have second one (iMac) and I swapped all the parts one by one including the LCD as well but the second one still working fine with all of the first one parts and the first one still not display on LCD. ???
