Replacing graphics cards due to screen flicker
Since a week ago, my iMac screen started to flicker. Basically I see multi-color bands flickering up & down the screen. Sometimes it's on for a few minutes and then it goes away, sometimes it stays on and then after a while screen goes completely dark. When I power cycle, it starts fine and then does the same thing all over. I have read various threads online and it appears that this could be related to a bad graphics card.
Couple of questions:
1. On this model iMac, can the graphic card be replaced? I read that it's part of the logic board on some earlier models
2. What can I check before buying a new graphics card (assuming that's an option) or a new machine?