My iMac Intel 27" EMC 2429 2.7GHz i5 has a large black area that looks like the back light has gone out. How do I know...

I'm NEVER going to know if just repairing the LED backlight would have done the trick. My friend just gave me an LCD screen for free and now the iMac looks as good as new. Lol! Thanks, Michelle!

I feel confident after speaking and troubleshooting with the Simply Mac tech yesterday. It's not likely the video card, but rather the LED screen or the LED backlight. '''HAS ANYONE EVER REPLACED THE 27" iMac LED Backlight Board? Part # 661-5980''' As shown here- http://www.powerbookmedic.com/27-iMac-LE... 54.html It is MUCH CHEAPER to try and replace the LED Backlight Board than the LED screen itself. Obviously, that would be the first thing I attempt to replace, it seems like the most logical next troubleshooting step. If anyone has any other information or suggestions I would appreciate it. Thank you