Random Shutdown Issue Possibly fan?
I bought a Macbook second hand off ebay with the intention of fixing it. The problem described was an easy fix, simply reinstall OSX and it should work fine. So I did this and discovered it had another issue in that it reset all the time. This was fixed by buying a new heatsink and sensor but after about 6 months it started to reset again. I tried all the obvious options, i.e. RAM, hard drive, fan speed but decided I had to face the fact that I needed a new logicboard. I ordered one off ebay and a new heatsink to go with it and guess what, it resets too.
So now I am completely stuck. I don't think it's the fan since I used to run that at full tilt with SMC fan control. However, I am not certain as the logicboard I have used as a replacement is a core duo 1.83 GHz, and the board it replaced was a Core 2 Duo 2.0GHz. The Macbook booted fine and worked without needing a reinstall, except for the keyboard and trackpad. Also, SMC fan control had trouble getting the fan to spin up. It just seemed to reset after about 5 minutes which was around the sort of time it used to reset when I had the 2GHz chip in there.
Is this a good question?