* AMD Radeon HD 6770 (512 MB) - Apple P/N 661-5967
* AMD Radeon HD 6970 (1 GB) - Apple P/N 661-5968
* AMD Radeon HD 6970 (2 GB) - Apple P/N 661-5969
We don't have a direct guide to replace the GPU in this series but this IFIXIT guide you'll get you mostly there: [guide|7575|Installing iMac Intel 27" EMC 2429 Dual Hard Drive Kit]. Go through the steps to Step 31 at which point you'll need to disconnect the SATA & power cables of your drives to finish freeing up the logic board. Once you get the board out you'll need to dismount the GPU board with its heatsink.
If your system is working now you may want to think twice here on this swap out.
'''First:''' You will need a real Apple GPU board as the boards firmware is custom.
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'''Second:''' It's a lot of work and the amount of improvement may not be what you expected unless you also upgrade the systems CPU to an i7 as well. So if that is what you are also intending on doing I would first do it making sure the system is working with the new CPU before going to the expense of replacing the GPU in case you have problems in the process.
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'''Second:''' It's a lot of work and the amount of improvement may not be what you expected unless you also upgrade the systems CPU to an i7 as well. So if that is what you are also intending on doing I would first do it making sure the system is working with the new CPU before going to the expense of replacing the GPU in case you have problems in the process (change out one thing at a time).
Here are your three GPU choices:
* AMD Radeon HD 6770 (512 MB) - Apple P/N 661-5967
* AMD Radeon HD 6970 (1 GB) - Apple P/N 661-5968
* AMD Radeon HD 6970 (2 GB) - Apple P/N 661-5969
We don't have a direct guide to replace the GPU in this series but this IFIXIT guide you'll get you mostly there: [guide|7575|Installing iMac Intel 27" EMC 2429 Dual Hard Drive Kit]. Go through the steps to Step 31 at which point you'll need to disconnect the SATA & power cables of your drives to finish freeing up the logic board. Once you get the board out you'll need to dismount the GPU board with its heatsink.
If your system is working now you may want to think twice here on this swap out.
'''First:''' You will need a real Apple GPU board as the boards firmware is custom.
'''Second:''' It's a lot of work and the amount of improvement may not be what you expected unless you also upgrade the systems CPU to an i7 as well. So if that is what you are also intending on doing I would first do it making sure the system is working with the new CPU before going to the expense of replacing the GPU in case you have problems in the process.