4 Replies Latest reply: Mar 25, 2011 8:11 AM by defined
natefoo Level 1 Level 1 (0 points)
Hi all,

I've been experiencing thermal shutdowns over the last few weeks and I suspect I may have temperature sensor(s) that have failed. If I generate high CPU load, the "CPU A Temperature Diode" reading skyrockets, up towards 125C where the system will power itself off to save the hardware. However, during this entire time, the "CPU Core 1" and "CPU Core 2" read between 65C and 70C. I have never seen them go higher than 70C.

In trying to fix this I cleaned out the cooling fins on the heatsink that sit in front of the fans, as well as cleaned off the old dried heat sink compound and applied new stuff. The result of this has been that the fans tend not to max out at 6,000rpm despite the CPU A Temperature Diode hitting high temps. Why they're not going higher is not apparent to me.

So it looks like the CPU Core sensors are bad? Could something else be going on here? Marcel Bresink's Temperature Monitor alerted me of an interesting thing, namely, that the Core Duo had a bug which would cause the core sensors to stop working after waking from sleep. However, I have both of the updates installed which provide a software patch for the buggy microcode. Details are on his site here:

http://www.bresink.com/osx/216202/Docs-en/faq.html

Is this CPU designed to step down voltage to run cooler(/slower) if it gets too hot? If so, the core temp sensor not returning a real reading would explain why the CPU will happily run itself off a cliff.

Sorry if this exact issue has been covered here before, but I couldn't find it after quite a bit of searching.

MacBook Pro 15" Core Duo Model A1150 (original MBP), Mac OS X (10.6.6)
  • tjk Level 7 Level 7 (24,180 points)
    Hi n, and welcome to Apple Discussions.

    natefoo wrote:
    I've been experiencing thermal shutdowns over the last few weeks and I suspect I may have temperature sensor(s) that have failed.


    Find the original install disc with the Apple Hardware Test on it. Boot from this disc while holding down the d key and run AHT to see if it will identify the fault.

    Is this CPU designed to step down voltage to run cooler(/slower) if it gets too hot?


    I have never heard that, but cannot say for sure.

    Message was edited by: tjk
  • natefoo Level 1 Level 1 (0 points)
    Hi tjk,

    Thanks for the response. My issue is resolved, so I'll post up in case anyone finds this thread in the future and is looking for answers. Unfortunately my resolution won't be very satisfying, since I pulled a co-worker's first generation Core 2 Duo (A1211) MBP out of a closet and swapped my disk into it. The CPU Core temps on this new laptop fluctuate quite a bit, which supports the suspicion that the sensors in my old laptop were dead.
  • tjk Level 7 Level 7 (24,180 points)
    Hi Nate,

    I do not understand, but it sounds like you've worked this out to your satisfaction, and that's what counts. Glad you got it resolved.
  • defined Level 1 Level 1 (0 points)
    Hey, seems i have the same problem. Random shutdowns for no reason,
    lost a lot of work already. can you tell us how you fixed it?
    thanks in advance