broken logic board but external screen works

[Thizzle]

Recently I had my early 2007 24" iMac's graphics card fixed. Three weeks later the main screen went all black but my external screen works and I'm able to use the computer just fine when I mirror the display.

I gave the imac to the same repair place that changed my graphics card and they saying the logic board is broken.

I was thinking the problem was display cable or something but logic board is a much more expensive thing to repair so wanted to double check here if its even possible for the computer to work with an external display if logic board is broken?

 

[ljonesj]

So the computer works with an external monitor right if it does then it not logic board its either cable from board to screen, screen or they busted something. if you can take it somewhere else to see if you can get it fixed

 

[Detrius]

Ditto. If external video works, it's not likely to be the logic board. It's possible the logic board isn't putting out a signal to the internal screen, but it's not likely (unless they broke something).

At the very least, the fact that external video is working means that your graphics card is working.