13 Replies Latest reply: Dec 22, 2010 8:46 AM by rkaufmann87
D. Ryder Level 1 Level 1 (0 points)
I have a late 2006 Intel iMac (Model ID iMac5,1) that is having trouble powering on. It will not power on unless I unplug it first, plug it back in and then push the power button immediatly. I tried resetting the SMC according to the procedure here: http://support.apple.com/kb/TS1587 (unplug, hold power button for 5 sec, release, plug in) but that did not solve the problem. I have also seen in the forums and elsewhere in the tech library an SMC reset methodology of unplug, hold power button, plug in, release button.

How can you tell if an SMC reset has occurred? Is there something other than a problematic SMC that could be causing my power-on problem? What is the correct SMC reset procedure for my iMac model?

MacBook, iMac 2007, iBook G4 & others, Mac OS X (10.5.8), 3 AirPort Express home network, Time Capsule
  • rkaufmann87 Level 8 Level 8 (49,005 points)
    Here is the correct procedure for doing an SMC reset on an Intel based iMac.


    _SMC RESET_

    • Shut down the computer.
    • Unplug the computer's power cord and all peripherals.
    • Press and hold the power button for 5 seconds.
    • Release the power button.
    • Attach the computers power cable.
    • Press the power button to turn on the computer.

    You can also try doing a PRAM reset.


    _PRAM RESET_

    • Shut down the computer.
    • Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
    • Turn on the computer.
    • Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
    • Hold the keys down until the computer restarts and you hear the startup sound for the second time.
    • Release the keys.
  • WZZZ Level 6 Level 6 (12,700 points)
    How can you tell if an SMC reset has occurred? Is there something other than a problematic SMC that could be causing my power-on problem? What is the correct SMC reset procedure for my iMac model?


    You should see a message about the SMC reset in the logs. Open Console in Utilities and go to system.log. You were using the correct procedure. Might be a good idea to do the reset with all peripherals except keyboard and mouse disconnected.

    You should also do a PRAM reset. At startup hold CMD-Option-P-R together until you hear two more chimes, three total, then let go.

    I'd open Disk Utility in Utilities, highlight the drive and choose Verify. If you get any errors, you will need to boot from the Install Disk and run Disk Repair from there. See "Try Disk Utility"

    http://support.apple.com/kb/TS1417

    You should also run the Hardware Test in Extended. It may be necessary to run it several times before it picks up any errors.

    http://support.apple.com/kb/ht1509
  • D. Ryder Level 1 Level 1 (0 points)
    Having never looked in the System Log before, I'm not sure I know what I'm looking for. However, a search on "system", "management", "reset" and "SMC" turns up nothing that would suggest a reset occurred. Looking at the time capture, I can't see that there's any evidence of an SMC reset, and it sould have been obvious as it was the first thing I did tonight. I did indeed do a reset unplugging everything (including the keyboard).

    So what exactly am I looking for in the log?
  • WZZZ Level 6 Level 6 (12,700 points)
    Sorry for the late reply. Now I'm not certain an SMC reset will be logged; before this, I was assuming it would be. In fact, I did an SMC reset last summer and reviewing my secure log where it would normally show up from that long ago, I see nothing. But if you did it according to that procedure, then I don't see why it wouldn't have taken effect.

    Have you tried the other suggestions above?
  • D. Ryder Level 1 Level 1 (0 points)
    1) SMC Reset using "unplug, hold power for 5, release, plug in": No change

    2) SMC Reset using "unplug, hold power button, plug in, release": Didn't fix it, but it turned the fan on full blast all the time, which is getting kind of annoying.

    3) PRAM Zap: Achieved. No change.

    4) Disk Utility - Verify: No errors, disk is OK.

    So I still have the problem, and now my fan is running full blast, too.
  • WZZZ Level 6 Level 6 (12,700 points)
    Tried running the Hardware Test?
  • den.thed Level 7 Level 7 (25,025 points)
    Question is which fan there are 3 in an Intel iMac, +(HD, CPU and Optical Drive)+ to check download the iStatPro Widget. > http://www.islayer.com/apps/istatpro/

    Or as WZZZ suggested above run the Apple Hardware Test, because it sounds like you have a faulty or disconnected temperature sensor.
  • rkaufmann87 Level 8 Level 8 (49,005 points)
    Reset the SMC once again that should take care of the fan problem. the instructions for an iMac are:




    _SMC RESET_

    • Shut down the computer.
    • Unplug the computer's power cord and all peripherals.
    • Press and hold the power button for 5 seconds.
    • Release the power button.
    • Attach the computers power cable.
    • Press the power button to turn on the computer.
  • D. Ryder Level 1 Level 1 (0 points)
    WZZZ: Apologies, should have mentioned the Hardware Test: 3 passes with no troubles identified.

    rkauffman87: I have repeatedly tried the "correct" SMC reset procedure to no avail. In all cases, I can start up immediately. But let it sit overnight and unplugging and replugging the power cord is necessary (I actually think the "correct" procedure only allows use of the start up button because the machine is unplugged and plugged back in). And I still can't find evidence in the log that an SMC reset has occurred. So even if I'm doing it right, I can't tell definitively that it has happened, unlike the PRAM zap and it's double chimes.

    The fan that is running is the CPU fan.

    Dumb question: isn't the SMC powered by a battery? Is it possible the battery has died?
  • WZZZ Level 6 Level 6 (12,700 points)
    isn't the SMC powered by a battery? Is it possible the battery has died?


    I don't think the SMC is but the PRAM is. There is a PRAM battery; it's a commonly available CR2032 Lithium button battery and its lifetime is around five years. It might be weak or dying. But I don't know if it directly controls the fan behavior. It might be related more to your initial question concerning erratic power on. This article lists what it does control.

    http://support.apple.com/kb/ht1379

    Not sure if this is your model, but just to give you an idea what might be involved in replacing it.

    http://www.ifixit.com/Guide/Repair/Installing-iMac-Intel-20-Inch-EMC-2105-and-21 18-PRAM-Battery/1082/4

    If it's just the CPU fan, it might be a bad sensor, but the Hardware Test, since you ran that 3 times, should have reported that. If you don't already have it or something like it (and you probably do, since you know it's only the CPU fan) I'd get free iStat Pro, so you can see the temps and fan speeds. Although, you seem to be saying the CPU fan is always running fast, even at startup, so that doesn't sound temperature related.

    http://www.islayer.com/apps/istatpro/

    If you can't get to the bottom of this on your own, I think it might be wise to bring it in to an Apple Store and let them run their diagnostics which are far more sophisticated than the Hardware Test; the Hardware Test might be missing something. I don't think they charge for that, but ask first to be sure.
  • D. Ryder Level 1 Level 1 (0 points)
    Solved it. The problem appeared to be that I was not letting be unplugged long enough. I unplugged it, held the button down for 10 seconds, then left it unplugged overnight, and held the button down 10 seconds again. Operations are back to normal now, including the fan.

    I don't know that leaving it unplugged overnight was necessary, but clearly the 30-60 seconds I left it unplugged in previous trials wasn't long enough. I'm an engineer but unfamiliar with the innards of Macs, but from this would guess the SMC gets its power from the power cord directly, and there's at least one capacitor of consequential size as part of the SMC. Unplugging it kills the power, pressing the button discharges the capacitor, and without juice, it forgets and resets to defaults. Not leaving it unplugged long enough causes the power supply to still trickle in power, and pressing the button doesn't drain it all. Hence it doesn't forget and doesn't reset.

    Or I'm full of it.

    Thanks to all who helped.
  • WZZZ Level 6 Level 6 (12,700 points)
    That's very interesting. Thanks for the feedback.
  • rkaufmann87 Level 8 Level 8 (49,005 points)
    Glad you got it figured out and thank you for the star.