Answer to: AMD Radeon HD 6750M 512 MB hardware upgradeHi I have a similar problem. But worst. My card stoped working. I have to get another one to have my iMac back. Presently only works with teamviewer, or maybe with an extra screen, which I didn't try yet. I would like to manage a card. Where's the best place to buy an used trustable one. There's a lot of AMD Radeon HD 6770M and 6750 M in the net, but I' m afraid it doesn't feet in my mid 2011 iMac 2,5Ghz intel EMC 2428 A1311 Thank you.