I just had a similar issue with my wife's MBP. I would not attempt to graft a different type logic board into the machine. Instead, I had great results taking out the logic board following the instructions on the iFixit site. I then searched the web for "a1260 logic board bake". You can use other terms, but the idea is to gather up some input from other users on how to prep your logic board for putting into an oven and baking it for a few minutes to anneal the solder joints and re-enable the nvidia chip and others. I was amazed at the number of folks who have apparently been able to fix their MBPs with this technique.
A few things to consider:
- The logic board removal and replacement is the hardest thing to do with these MBPs and you will need a few hours to get it all done.
- You need to make sure you have adequate tools and small parts bins ahead of time. I have a magnetic small parts dish, among other things. Apple never met a screw they didn't like. For that matter, they must have a department that engineers new ones all the time :-) Even the iFixit instructions don't really give you the feel for how many little screws of subtly different sizes come out of these Macs.
- I chose 375F for 7minutes, thirty seconds. My setup included a cookie sheet, clean foil on the sheet, four 1" crumpled balls of foil to hold the logic board off the sheet (heat all around), and I removed all the stuff that looked like it might melt (all tape, all bumpers, the two black plastic clip-on washer thingies near the top of the board that don't look like they are soft and removable plastic, but are!), and covered the RAM connectors with a smaller piece of foil just in case.
- You may want to discuss the temperature performance (accuracy) of the oven with anybody who uses the oven the most. If you over heat the board, you will ruin it for sure. The solder becomes softer than normal at 375-400F. Over 400F, most of these solders start to go liquid which is bad. The goal is to anneal cracked joints, which is a good ways away from being "liquid".
- I read a blog in which the "fixer" had his whole family pray for a good outcome. Your belief may differ, but I took no chances and had my family do the same thing.
- DO NOT ATTEMPT TO RE_USE THE OLD THERMAL PASTE! iFixit sells some excellent paste, I am sure, but since I couldn't wait I went to the local electronics store and made sure I cleaned all heat sink and component surfaces with alcohol.
The end result is that it worked! Good luck!