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iMac Randomly Shuts Off

2857 Views 7 Replies Latest reply: Oct 23, 2012 12:40 PM by davmax7 RSS
Thehoofbite Calculating status...
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Apr 21, 2012 4:58 PM

I have a 20 inch iMac.  Believe it is the 7,1 model from mid-late 2007.


A while back in started just intermittently shutting off.  Wait a few seconds and it boots back up and all is well again for some random amount of time.


It happens during all sorts of uses.  Simple browsing, working in PS or making a movie, listening to really doesn't matter what I am doing it will happen whenever.


Sometimes it will do it once or twice per day, sometimes it will stay on for a couple of weeks before doing it.


I opened it up and dusted it all out thinking that maybe it's overheating.


Still does it.


All my temps are reading in the 40C range except for the ambien temperature which is around 23-24C.


I don't have a clue what the deal might be. I've worked in PS for hours on end at times and nothing happens but then at other times I will just be browsing the web and it will turn off. 


Is there some sort of system report file I can read to try to figure this out?



  • den.thed Level 7 Level 7 (23,400 points)
    Currently Being Moderated
    Apr 21, 2012 5:22 PM (in response to Thehoofbite)

    Check the RAM, you may have a loose or partially seated module. Remove and reinstall the modules pushing real hard on them with both thumbs to insure that they are fully seated in the slots.


    Then if it is still acting up, run the Extended Apple Hardware Test from the System Disc that came with that iMac. > Intel-based Macs: Using Apple Hardware Test

    iMac, Mac Mini, iPad, iPods, Mac OS X (10.6.8), (10.7.3) Safari, iTunes, iPhoto
  • den.thed Level 7 Level 7 (23,400 points)
    Currently Being Moderated
    May 1, 2012 4:56 PM (in response to Thehoofbite)

    The next time it acts up and you get in going again, go to Applications / Utilities  and open the Consol and check All Massages.


    Run the Extended Test.

  • RalphieRulz Level 1 Level 1 (0 points)
    Currently Being Moderated
    May 3, 2012 10:12 AM (in response to Thehoofbite)

    I am having the same problem. I've replaced the RAM and hard drive. It shuts down usually once or twice a day. I'd appreciate any insight people have.

  • AnilKiran Calculating status...
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    May 3, 2012 10:27 AM (in response to Thehoofbite)

    Run an extended test, this might take a long time. AHT (Apple Hardware Test) is what AASP will do when you give the product for service. Extended test will check each component, you will find some errors if issue with h/w. If not logic board is faulty. Also check for cooling solutions, iMac has major issue with fans. If iMac is over heating, frequent shutdown is common.

  • davmax7 Calculating status...
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    Oct 23, 2012 12:40 PM (in response to Thehoofbite)

    I have an iMac circa 2009. Have been experiencing the same spontaneous shutdowns.


    After much research I found an article by an Apple engineer (sorry, failed to bookmark) which explained the cooling system of the iMac. These computers are not cooled directly by internal fans, rather by ambient ventilation and heat displacement. Internal fans are most efficient when speeds are at factory setting.  The use of any kind of external fan only interferes with the system's cooling machine. Lastly, screen brightness should never be set at or near full brightness as heat from the screen only adds to the general temperature of the machine.


    Implementing these 3 suggestions solved my spontaneous shutdowns. Using Fan Control (not iStat) I saw my CPU, HD, GPU temps drop by almost 10 degrees C. Lion's a tad more spunky. Most importantly, my computer isn't shutting down anymore as if someone had pulled the power cord.


    Over the past several months that I have tried to resolve this problem I have done everything from completely disassembling the machine, cleaning fans, checking heat sensors, switching RAM, power cords, uninstalling suspicious apps, all to no avail. In other words, this has been a long, nerve-wracking process for me. Not understanding at all how an iMac really manages heat displacement and prompted by some misleading suggestions to ramp up fan speeds, I was compounding the heat issue problem.


    This resolution may not work in your case, but it did for me. Please post comments if this helps your shutdown problem.


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