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Sudden restarts and shutdowns on iMac

9414 Views 36 Replies Latest reply: Apr 9, 2009 11:55 AM by dudie RSS
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randmc323 Calculating status...
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Jan 14, 2009 9:51 AM
I recently bought a refurbished iMac from Best Buy. When I inspected the unit after I unpackaged it, nothing appeared wrong externally. Also, the setup and installation of the OS went smoothly. However, after turning it on and browsing the web on Safari, the iMac suddenly shuts down. I thought that the power cord might've had a short in it at first, but have since moved away from that conclusion. Now, whenever I turn on the computer it will boot up fine and then suddenly shutdown or restart.
And as I write this, there is a new symptom: as soon as the iMac loads the desktop, the fans start up really loudly and then the computer shuts down.

Help is much appreciated.
iMac late '08, Mac OS X (10.5.6)
  • rkaufmann87 Level 8 Level 8 (40,505 points)
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    Jan 14, 2009 3:42 PM (in response to randmc323)
    Before taking it back try this, if these don't work call Apple for support. If the machine is covered by AppleCare or is less than 90 days old you are entitled to free phone support. The phone number is in you manual

    Try doing a SMC and PRAM reset by:

    1. Turn off your iMac and unplug everything from it for 30 seconds.

    2. Plug in the power cord, keyboard and mouse only.

    3. Press the power button and immediately hold down the Option, Command, P & R keys until you hear the second gong then release the keys. Your machine will start up normally, then check for the issues you are having.
    Imac Mid 2007 2.8 Core 2 Duo 4 GB RAM, Mac OS X (10.5.6), LaCie 320, 500 and 750 GB Quadra D2's, iPod, Airport Extreme, Airport Express
  • den.thed Level 7 Level 7 (23,325 points)
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    Jan 14, 2009 8:15 PM (in response to randmc323)
    Why not buy a refurbished iMac directly from Apple?

    http://store.apple.com/us/browse/home/specialdeals/mac?mco=MTE3NjY
    17" Early 2006 Core Duo - 2GB RAM -, Mac OS X (10.5.6), - Maxtor FireWire HD's - WD Pocket HD - Epson - 80GB Classic - 2GB Nano
  • _aperture Calculating status...
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    Jan 14, 2009 8:26 PM (in response to randmc323)
    well, i have the same/similar problem - random restarts. and mine is a new 24"/2.8 GHz/10.5.6/iMac bought about 5 months back. problem started about a month back and incidentally a few days after i upgraded to 10.5.6. so, i assumed the issue was with the upgrade. please see the thread http://discussions.apple.com/thread.jspa?threadID=1835711&tstart=0 for my initial experiments. i have since concluded the issue is not 10.5.6.

    i then called apple and they tell me that they have had a couple of similar cases and the issue was the main DC power cable which had to be replaced. they have ordered one for me and am waiting for the part to arrive and for the repair. hopefully, the cable indeed is the issue and the problem will be solved once and for all. will keep you posted.

    you may want to investigate along similar lines...
    24" iMac 2.8 GHz, Intel/Unibody MacBook Pro, Mac OS X (10.5.6)
  • FetterDave Calculating status...
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    Jan 21, 2009 3:56 AM (in response to _aperture)
    Our 24" iMac has recently begun having the sudden restart problem as well. Resetting the PRAM had no effect; I'm taking it to the local Apple Store on Friday and will post again after I talk to the folks there.

    Thank goodness for AppleCare.
    iMac, Mac OS X (10.5.6)
  • _aperture Level 1 Level 1 (0 points)
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    Jan 21, 2009 4:04 AM (in response to _aperture)
    Even after the power cable was replaced, the problem exists. So, now they are going to take it to the service center and observe/diagnose further...
    24" iMac 2.8 GHz, Intel/Unibody MacBook Pro, Mac OS X (10.5.5)
  • Scott Fields Calculating status...
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    Feb 12, 2009 8:11 AM (in response to _aperture)
    Replacing the power cord will not fix it. I work for a AASP and I have been round and round with 3 of these things. I'm almost convinced that the original power supply has a heat issue that causes the voltage regulator chips to overheat and swell up and separate from the board. I will make another pst later today when I have tested this more.
    MacBook 2.16, 4GB RAM, 320GB HD, Mac OS X (10.5.6)
  • nuvo Calculating status...
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    Feb 12, 2009 8:37 AM (in response to Scott Fields)
    We have a long history with this problem. So far 4 out of 10 iMac purchased at the same time had this problem. We have replaced the logic boards - then the machine works for a day or two then fails. We next replace the power supply, works for a day or two then fails. We suspect thermal issues, no help from Apple - then read about the cable harness and that fixed the problem. The next machine that fails we plan to swap the cable first. I just want to note that some of the machines are up and running now for months with just the replacement of the logic board or power supply. Nothing seems to remail consistent but the problem.
    iMac, MacBkPro, MacMini, MacPro, Mac OS X (10.5.6)
  • highcountry Calculating status...
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    Feb 12, 2009 12:17 PM (in response to randmc323)
    I have a 20' iMac purchased less than a year ago. Started having the same problems a few months ago. Would restart at random times, even when in sleep mode. An Apple cert. tech replaced the logic board and power supply. Everything worked for a few months, but now the same issue is back. In addition the fan speed increases dramatically even when the temps are normal. Surprisingly, the tech indicated the the logic board he put in was used and thus may have gone bad again. So it will be back again for another logic board.
    Would be nice if folks posted any successful resolutions to this issue.
  • highcountry Level 1 Level 1 (0 points)
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    Feb 13, 2009 9:41 AM (in response to Scott Fields)
    Scott,

    Have you determined whether you believe the heat from the power supply has damaged the voltage regulator chips? Very interested in your answer. And if so, why not on all iMacs?
  • Bethos Calculating status...
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    Feb 13, 2009 9:48 AM (in response to randmc323)
    I'm having the same problem. iMac was new in August '08. A few weeks ago (Jan '09) it restarted for no reason. Became more and more frequent over a week. First it was a few times a night, then every hour and then every 2-3 mins. Took to apple store - they replaced the power supply. Issue re-appeared in less than 24 hours after repair. Took back to apple store, they checked the internal power supply cable because there was apparently an issue with a previous version of the cable, but I have the updated one. Also said the logs aren't showing anything unusual and the apple store hasn't been able to re-create the issue.
    iMac, Mac OS X (10.5.6)
  • Scott Fields Level 1 Level 1 (5 points)
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    Feb 13, 2009 6:32 PM (in response to highcountry)
    I did find that one of the voltage regulator chips was crispy and the cold solder joints was loose. I replaced the power supply and the computer has been running for 2 days now. I left it running in the sop for the weekend. I will see what has happened on Monday when I return to the office.
    MacBook 2.16GHz 4GB RAM, Mac OS X (10.5.6)
  • highcountry Level 1 Level 1 (0 points)
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    Feb 13, 2009 8:15 PM (in response to Scott Fields)
    Scott,

    Do you believe those regulator chips were damaged by heat from the power supply or the power supply itself not providing adequate or spiked power surges?
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