Yesterday I swapped MBP early 2011 logic board to mid 2012 2.3 Ghz board. I had the same problem with LVDS cable as casagrande2407 mentioned. 2012 board was already with heatsink preinstalled (the seller told that it is a brand new logic board ). I watched several videos on MBP 2012 teardown and noticed that there is no heatsinks on Platform Controller Hub and Thunderbolt port controller, so I decided not to install heatsinks from dead board. While I'm writing this the hottest part of the board is CPU and its temp. differs from 33 C to 40 C. My MBP was lying on shelf for 2 years and now its alive! I'm really glad!