I am currently performing this upgrade from a Core2Duo to an i7-870, swapping out the logicboard. So. It boots. It's alive! Snags: - 1. The i7 needs a different heatsink from the Core2Duo. If you just buy a bare logicboard, as I did, you need to also get hold of the correct heatsink. Part number 730-0584. Cost bumped. 2. Fans running very high RPM and loud. 3. CPU running very slow. Despite now being shown as an i7 2.93GHz under About This Mac. Geekbench gives 32bit single core ~900 and multicore ~3000. Hardly an improvement so far. I too eventually noticed the new connector on the new logicboard for a "Skin Temp" sensor. Not present on previous logicboard. Running Apple Hardware Test gives the following error 4SNS/1/C0000008:TS2P--124. In the Apple Technician Guide (imac_27_late09.pdf) this means "Skin temp sensor (Quad-core models only) is damaged or disconnected from top of logic board." I tried shorting the skin temp connector with some bare wire. Nasty, and did not work. Going to try to get hold of a...
I installed the iMac 2011 Radeon 6970 1GB graphics card. It's hotter than the old card and I can hear the fan working, but not too much. No crashes, nice and stable. Yes, I ended up using this for video editing: Premiere and After Effects - the Mercury Playback Engine uses it. Recommended upgrade.
