Backlight dim in a part of the screen

"It is not a graphic issue. What's a strange solution? It is definitely not a graphic card. Of course, it is possible to fix it but it is very hard.

1. In all cases that I had only the left side of the screen was not working.

2. When I dissembled it I noticed that it faulty lcd panel (factory defect). I can explain what I mean. It appeared that all pins of the plug-in on the left side of the backlight lamp are not in the right position. For example, pin 1 on the place of pin 2, pin on the place of pin 3 and so one.

3. That's why, in order to repair it you should dissemble all screen and solder backlight plug-in anew. And it is very hard. I have spent 3 hours to repair it. And you also should be very careful not to damage lcd screen and other parts of the screen.

Next time I can make tutorial how to fix it if someone still need it."

"Hook it up to an external monitor to test. There was a repair program on the 2011 GPU on your series of machine and we can address that after you have checked it.

Please give us the last four figures of your serial number so I can check it out for this:

iMac (27-inch): AMD Radeon 6970M Video Card Replacement Program

Apple has determined that some AMD Radeon HD 6970M video cards used in 27-inch iMac computers with 3.1GHz quad-core Intel Core i5 or 3.4GHz quad-core Intel Core i7 processors may fail, causing the computer’s display to appear distorted, white or blue with vertical lines, or to turn black. iMac computers with affected video cards were sold between May 2011 and October 2012.

If your iMac has an AMD Radeon HD 6970M video card and is exhibiting any of the issues described above, choose one of the following options to arrange to have your iMac evaluated:

Before you go in for service, please back up your data. Learn more about backup options.

If the iMac (27-inch) meets these requirements, Apple will replace the video card free of charge for four years after the first retail sale of the computer."