A clever IT engineer from Germany (I’m half German and I can speak the language… sort of) seems to have figured out what causes the sudden MacBook shutdowns. The short version is it’s a short caused by varying temperatures. It doesn’t explain why for some people it happens shortly after waking from sleep, but it seems the most plausible explanation.
The phenomenon seems to be caused by the cable between the heat sensor and the CPU’s heat sink being too short.
The heat sink expands during operation and gets into contact with the sensor cable and melts the cable’s isolation. This in turn causes a short circuit and, thus, the immediate shutdown of the Macbook. As the heat sink is cooling down, the heat sink contracts to the point that it looses its contact with the cable and breaks up the short circuit. You can now boot again. Just until the processor heats up and the heat sink and the cable have contact again…
If this proves to be the reason then there might be a quick fix, specifically you would not have to exchange your mainboard or RAM.
That sounds like good news to me.
[via Digg]
Regarding Macbook Pro shut down..I think this directly relates to this issue...the heat sensor or at least its functionality. I tried several times to leave my laption on its side with the screen open like a book standing on its side for ten minutes or so rather than leaving it flat on a soft surface which I knew would overheat the laptop and found to my surprise that it just shut down in so doing. Apparantly side placement is a Verboten position. As to whether this is a heat issue or some other connexion to this issue, it is interesting since my laptop does not shut down randomly othewise. I have had the motherboard replaced as it was the first version. The fans seem to go on when it is very uncomfortably warm so I guess it is working as specified otherwise.