LED 4 indicates that the iMac is detecting over temperature conditions That is not correct on this model of iMac: LED #1 (left-most) Indicates that the trickle voltage from the power supply has been detected by the main logic board. This LED will remain ON whenever the iMac is connected to a working AC power source. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power source is disconnected or the power supply is faulty. LED #2 Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly. LED #3 Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement. LED...
As I was troubled by the conflicting information on this page/site, I wanted to testify I did just complete replacing the video card in my A1225 / EMC2267 24" iMac. I bought the Mac new from Apple in 2009 with the ATI Radeon 4850 HD video card upgrade. After 4 years, the VRAM died...the picture would scramble at the logon screen unless I booted into safe mode. In safe mode, screen covered in blue dots, TechTool Pro confirmed bad VRAM. I purchased a new card from Impact Computers in Florida. I had to fully remove the logic board to get at the video card, but with only three more screws it pulled free from the MXM connector, heat sink and all. I've got pictures of the whole process if anyone's interested. I'm confident one could upgrade the nVidia GT120 or 130 mid-line machines to the ATI card the same way. It may be the baseline machines (9400M graphics) don't have the MXM socket installed on the motherboard and are non-upgradeable.
so I actually have the broken GPU (the ATI one) I pulled from my iMac when I wrote this guide. I looked at the edge connector and curiously it doesn’t look like either one of your pictures. My card has a single notch in the center of the connector and both ends go all the way to the edge of the card. If you look closely at the first of the last 3 photos in the guide you can see it.
The wrong card shouldn’t damage the Mac. It just won’t work.
Having done this procedure 6+ times now, I can tell you it's much easier if, instead of holding the panel up by the "bottom" as illustrated in the guide, instead raise it by the "left" side. It gives you (me) much more room to get fingers behind the connector.
May have been obvious to some, but this little adjustment didn't jump out at me until the 2nd or 3rd rebuild.
If you're going to try and substitute parts, I would start with the website I bought my video card from (http://www.impactcomputers.com/apple-ima...) and see if the video card(s) for that particular 2011 iMac match any of the part numbers aaaidan shows above.
I picked out one of the 2011 iMacs at random on the website and while the actual card looks the same (size and MXM connector) the heat sink is completely different. But you could try and dismantle the heat sink from the old and new cards and swap them. I would love to know if that works. An AMD Radeon HD6750M upgrade would be sweet :)
so I actually have the broken GPU (the ATI one) I pulled from my iMac when I wrote this guide. I looked at the edge connector and curiously it doesn’t look like either one of your pictures. My card has a single notch in the center of the connector and both ends go all the way to the edge of the card. If you look closely at the first of the last 3 photos in the guide you can see it.
The wrong card shouldn’t damage the Mac. It just won’t work.
Maybe because it would interfere with the bracket you have to put back on in step 21?
Having done this procedure 6+ times now, I can tell you it's much easier if, instead of holding the panel up by the "bottom" as illustrated in the guide, instead raise it by the "left" side. It gives you (me) much more room to get fingers behind the connector.
May have been obvious to some, but this little adjustment didn't jump out at me until the 2nd or 3rd rebuild.
If you're going to try and substitute parts, I would start with the website I bought my video card from (http://www.impactcomputers.com/apple-ima...) and see if the video card(s) for that particular 2011 iMac match any of the part numbers aaaidan shows above.
I picked out one of the 2011 iMacs at random on the website and while the actual card looks the same (size and MXM connector) the heat sink is completely different. But you could try and dismantle the heat sink from the old and new cards and swap them. I would love to know if that works. An AMD Radeon HD6750M upgrade would be sweet :)
When I bought my iMac new, I remember the ATI card being the top-of-the-line option.