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I have a 2011 27” iMac with a 3.4Ghz Core i7 processor. A week ago the screen began to flicker intermittently, with the image on the screen sometimes being interrupted by horizontal lines the full width of the screen but varying depth and often much lighter than the image.
Obviously, my first thoughts had been that there was a problem with the video card. I am aware that the AMD Radeon 6970M video card in my machine is prone to failure and subject of an Apple replacement programme. My iMac’s serial number is one of those in the potentially affected batches.
After trying a number of standard trouble-shooting techniques, including a simple reboot, I eventually reset the PRAM and the problem seemed to go away. For good measure I also reset the System Management Controller.
I then ran Apple’s extended Hardware Test twice, but no problems were found.
At that point it seemed as if it was a case of ‘problem solved’, even though I didn’t know what the root of the problem actually was or how my actions had resolved it.
Big mistake. After a week of running perfectly, the flickering screen has returned. So I ran the extended Hardware Test again, but with the same result - ‘no problems found’.
Has anyone experienced a similar problem and can offer advice on how to solve it before I lug my machine to the nearest Genius Bar?
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