Chosen Solution
I’ve got 2 identical iMac’s here (1.83 Ghz Core Duo version), whit 2 defective screens. One has the typical vertical coloured lines (display failure not logicboard), the other one is 1rd black at the right side (the other 2rd is working fine) . Now I thought about fixing one of those 2 (the one whit the 1rd black should be easier), but i’m unable to find any schematics nor any fixing guide. Does someone has any idea? If necessary I could make some pictures. /edit: So here is a picture from the one that is 1 third black, or in this case 1/6 black and 1/6 white, this is changing each boot. As I said it’s the screen not the logicboard. The division is exactly between the 4th and 5th ribbon from the circuit board of the screen to the screen front.
The most common problem with this series was bad capacitors. Open them up and examine the approximately 24 “cans” for swelling and/or leakage. UPDATE 4/17/16 Here’s how to replace the display: iMac Intel 17" Display Replacement
