Screen will not light up unless external video is connected
Hi! I've got an odd 15" aluminum that will not show video on its own screen unless it is connected to external video, in which case it comes on, and the external screen works fine as well. I've tried cycling through the external display modes, and booting up in each one. I've tried resetting the PMU, which works, but the machine's PRAM will not reset -- it just sits on a black screen endlessly. It's a shame, because I think a PRAM reset would probably fix the issue. I've tried another topcase/keyboar
Occasionally, just randomly, the screen will light up with no external video attached, but it seems to be about one of 10 attempts, and like I stated, randomly, and not in response to anything in particular.
I'd hate to conclude that this is a bad board, and it seems like there must be a fix. It seems as if something is "stuck". Anyone know how to reset the PRAM without the keyboard? There are power and PMU power-on pads, but none for PRAM that I know of.
I believe, if it's like mine, that the problem is a severed wiring harness to the display at the upper right corner of the computer case. I have the same issue and this computer is known for an issue of a bad hinge. I knew, and perhaps you felt it too, the a slight "crunch" in the area of the hinge every time I opened and shut the lid was that it was gnawing on the wiring and sure enough, in time, the screen went blank similar to yours? I'm looking for a way to replace the wiring harness but not much success. I've found the part for as cheap as $15 but no instruction as for replacement. If you find this may be your issue and come upon instructions, please let me know.