i7 iMac - weekly SMC reset required?

Discussion in 'iMac' started by NGL, Apr 24, 2010.

  1. NGL macrumors member

    Joined:
    Feb 28, 2010
    #1
    It's happened twice this month - my CPU fans will suddenly rev up to 4,000 RPM, and iStatPro will show the CPU temperature as "--". The first time it happened, I was worried that the machine got too hot. The second time, I had just sat down at the computer in the morning... the top of it was hardly even warm.
    Both times, after shutting down and rebooting the fans went back to normal, but the computer performed poorly in graphical tasks such as rendering and gaming until I do an SMC reset, which brings it back to normal.

    I haven't installed the recent 27'' iMac SMC update, because I have no need to use the computer in target mode.

    Thoughts?

    -Nick
     
  2. iLog.Genius macrumors 601

    iLog.Genius

    Joined:
    Feb 24, 2009
    Location:
    Toronto, Ontario
    #2
    If you're needing to reset the SMC every week, either there is something wrong with your computer or you have software causing the increased fan speeds.

    1) try a new user and see if the fan speeds change there
    2) do you have any fan control software?
    3) any background processes that might be increasing the load on the CPU which might cause the fans to speed up?
    4) might have to do a clean reinstall to isolate the problem

    If none of those helps you, hardware might be bad.
     
  3. NGL thread starter macrumors member

    Joined:
    Feb 28, 2010
    #3
    Thanks for the reply.

    1) I haven't tried a new user, right now there is only one account
    2) I don't have any fan control software, just iStatPro to monitor the speed
    3) No background processes. It's worth noting that the second time it happened, iStatPro showed my computer was 99% idle. So it's more likely a bad heat sensor than an actual heat problem.

    Now that I think about it, both times it happened I was running Modern Warfare. That can't be coincidence, can it?

    -Nick
     
  4. NGL thread starter macrumors member

    Joined:
    Feb 28, 2010
    #4
    Happened again this evening (2nd time today) while watching a Friends DVD. So that rules it out as a Call of Duty problem. Same issue, CPU fan at around 4k RPM and CPU reading of "--" in iStatPro. Computer was fairly warm on top, but certainly not as hot as it has been, so it's still looking like a funky heat sensor or something.
    Haven't done an SMC reset, just shut down and booted up, which stops the fan and resets the temp reading.
    Might install that SMC update tomorrow, even though it's not supposed to have anything to do with this issue. You never know.

    Any more input would be great.

    -Nick
     
  5. iLog.Genius macrumors 601

    iLog.Genius

    Joined:
    Feb 24, 2009
    Location:
    Toronto, Ontario
    #5
    1) Create a new user (see what activity you get there)
    2) do a reinstall. (The reinstall will of course be the final step, it will either fix it or won't. Either way, you'll know your answer.)
     
  6. NGL thread starter macrumors member

    Joined:
    Feb 28, 2010
    #6
    The problem with creating a new user is that the fan problem could occur once a day, or once a week... and I don't want to use a temporary account for an entire week while all my stuff in on my main account.
    That said, I'll give it a shot since I have no other ideas.

    EDIT: Oh, and what about that recent SMC update? Should I run it just in case?

    EDIT2: The issue never happened for the first few weeks I had the machine... may have started when I did the 10.6.3 update.

    -Nick
     
  7. NGL thread starter macrumors member

    Joined:
    Feb 28, 2010
    #7
    Ok, sorry for all the multi-posts...

    For anyone following the issue / with similar issues:

    Done some sleuthing, and it appears that, in a heat emergency, the computer will first try to cut it's processing by half to deal with the issue. If that doesn't help it shuts itself down.

    So my issue very well may be:

    Faulty heat sensor thinks it's hot > triggers fan at 4000 RPM / triggers 50% performance lock.
    Reboot clears the sensor reading and restores normal fan speed and heat readings, but does NOT reset the 50% performance lock, which explains why Modern Warfare runs like crap until I do an SMC reset.

    Going to reinstall and NOT hit 10.6.3 and see what happens.

    -Nick
     
  8. iLog.Genius macrumors 601

    iLog.Genius

    Joined:
    Feb 24, 2009
    Location:
    Toronto, Ontario
    #8
    You could also try Apple Hardware test to see if anything gets flagged.
     
  9. NGL thread starter macrumors member

    Joined:
    Feb 28, 2010
    #9
    Tried that, everything checked out.
    Wiped the drive and reinstalled Snow Leopard 10.6.2 from the disc, and didn't upgrade to 10.6.3. The next morning I got another CPU fan surge.
    Guess I'll call Applecare. Buying a Mac used to be so simple... (5th 27'' iMac in two months)

    -Nick
     
  10. i7QuadCoreMania macrumors 6502

    Joined:
    Nov 10, 2009
    #10
    Hate you tell you this but the CPU temp sensor connector is loose.

    Do a hardware test the next time it happens with the Applications disk.

    The error code will be cryptic, this is the error code for that:

    TA0P
    Ambient temp sensor
    stand-alone part, located near CPU fan
    Check sensor cable connection to logic board, run CPU fan test, check air flow.


    If you get that code the cpu temp sensor needs to be reseated, cannot do this without taking the Logic board out of the iMac. You'll have to bring it in for service.;)
     
  11. iLog.Genius macrumors 601

    iLog.Genius

    Joined:
    Feb 24, 2009
    Location:
    Toronto, Ontario
    #11
    OP tried the Apple Hardware Test and did not report anything.
     
  12. i7QuadCoreMania macrumors 6502

    Joined:
    Nov 10, 2009
    #12
    I had a similar problem, it is intermittent, you have to catch it when it is happening for the error to show up. I too called Applecare had me reset smc, all that BS did nothing for me, problem would come back.

    Like I told them, I was using a widget, istat nano and noticed the cpu temp was -- when the fans were going crazy, all fans running at full blast.
    Being an IT person by trade, I decided to tackle the problem myself, since my 27" was not infected with the Yellow or deadpixels, wanted to keep this unit if I could.

    I opened up iMacs before, upgraded my 24" previously to upgrade the HDD. Was planning to do a SSD upgrade on my 27" and figured to check out the cpu temp sensor, after looking at the Apple service manual for removal of the logic board, the sensor is on the backside of the board and requires removal of the logic board to access.

    What I found, was a Temp sensor plugged in half way!!! damn cheap Shanghai labor.:mad: reseated all cables, installed my SSD and Bluray drive(come to find BD is useless in OSX)haven't had the problem ever since, quiet and fans always running normals speeds whenever I check it with istat nano.

    While I don't recommend opening up your unit, your symptoms seem too similar. Contact apple to see if anything can be done. But like a car which behaves when the mechanic is around, it's hard to fix if you can't reproduce the problem.:rolleyes:
     
  13. NGL thread starter macrumors member

    Joined:
    Feb 28, 2010
    #13
    Thanks very much for posting, I'm sure that I'm having the same issue as you did.
    Spoke to Applecare this morning, they asked me to bring it in to my local store. From my experiments, they diagnosed a heat sensor issue. When I bring it in to the Apple store tomorrow, I'll ask them to specifically check the seating on the CPU heat sensor.

    -Nick
     

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