I suppose most people here know about graphic card issues in mid-2011 iMacs and Apple's graphic card replacement program. Well, a couple of months ago my iMac seemed to have joined the ranks - white screen, blue and pink stripes, etc. I live in a fairly remote town about 400 km away from the Apple-authorised service center and, since this was not the only desktop in the house, I did not take it for repairs right away. A few days ago I had a chance to send it down with a friend, but when I turned the computer on, the defect was not there. Typical. I called the service center and they said they would not replace the card unless they know it is defective. I ran AHT, Unigine Heaven benchmark for quite some time, asked my kids to play some games, etc. - still no issues. I didn't want my friend to go through all the trouble of taking iMac for repairs for nothing, so I didn't send it. Sure enough, today we got white screen with stripes again while watching an HD video online. However, what happened next was a bit puzzling. iMac tried to reboot twice on its own with a striped screen, successfully rebooted on the third attempt (no stripes) and continued like nothing happened! I ran Unigine, the graphic card was heating up to 80-90 Celsius - still no defect! Now my daughter is finishing her movie, I believe so far there are no issues (30 minutes or so).
This got me wondering if perhaps my issue is not discrete AMD graphics but Intel graphics? Does iMac 2011 work as a dual-graphic system? If the discrete graphic card is faulty, shouldn't the defect always show under extensive 3D load rather than during considerably less demanding 1080p video viewing? The initial defect also appeared when we watched some YouTube videos, but the next day it was also showing in games. This time 3D load didn't do anything. How can I know for sure my discrete graphic card is defective and thus eligible for a replacement program before I take my iMac to the shop?
This got me wondering if perhaps my issue is not discrete AMD graphics but Intel graphics? Does iMac 2011 work as a dual-graphic system? If the discrete graphic card is faulty, shouldn't the defect always show under extensive 3D load rather than during considerably less demanding 1080p video viewing? The initial defect also appeared when we watched some YouTube videos, but the next day it was also showing in games. This time 3D load didn't do anything. How can I know for sure my discrete graphic card is defective and thus eligible for a replacement program before I take my iMac to the shop?