Hi There, mine is a late 2011 model iMac desktop and I'm having trouble with the display screen. It's coming up with pink and yellow vertical strips. The tech says it could be graphics card. The online spec for my late 2011 model iMac suggests it is - (AMD Radeon HD 6750M graphics processor with 512MB of GDDR5 memory). Can you please tell me if that's right. Thank You.