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  1. #1
    iMac random shutdown

    Member Since
    Oct 26, 2012
    Posts
    9
    iMac random shutdown
    Hello Mac Gurus,

    I have an iMac from 2009 that shuts down itself. The problem started a few weeks back. iMac would just die on itself several times a day. I reinstalled the OS from disk (erased HDD) but it didn't resolve the problem. However, I noticed that most shutdowns were triggered when I tried to install a software or tried to play with the hard drive (like trying to open Disk Utilities).

    After installing the OS, I figured that it would die 7 out of 10 times when i tried to open disk utilities.

    I took it to a local apple store and a genius used MRI (Mac Resource Inspection, I believe) to diagnose the problem. No problem were detected. He then erased the HDD and reinstalled same OS from network. It seemed to resolve the problem but now I have it back in my apt and it still keeps dying on me. Any suggestion ?

    Thanks in advance

  2. #2
    iMac random shutdown
    chscag's Avatar
    Member Since
    Jan 23, 2008
    Location
    Fort Worth, Texas
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    45,176
    Specs:
    27" iMac i5, 3.2 GHz, iPad 3, iPhone 5c, iPhone 6+, 3 iPods, Yosemite
    Sudden shutdowns are almost always due to hardware problems. It could be caused by the power supply in the iMac or even bad memory. If it's intermittent, which most sudden shutdowns are, they're very difficult to find even with diagnostics. And reinstalling the operating system is not going to resolve a hardware problem. What you can try for now is use your iMac on a UPS system to insure it has steady AC power. But even that might not be enough.

  3. #3
    iMac random shutdown

    Member Since
    Oct 26, 2012
    Posts
    9
    Thanks Chscag for the response. With MRI, a genius was able to look at the power drawn by the power supply and it was normal. So I don't know if it is a power supply issue. I do, however, believe that it might be HDD problem.

  4. #4
    iMac random shutdown
    chscag's Avatar
    Member Since
    Jan 23, 2008
    Location
    Fort Worth, Texas
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    45,176
    Specs:
    27" iMac i5, 3.2 GHz, iPad 3, iPhone 5c, iPhone 6+, 3 iPods, Yosemite
    It would be unusual for a hard drive defect to cause the machine to shut down completely. Hard drive problems can cause sudden reboots though. Although I would not rule it out. However, swapping out a hard drive in an iMac is a rather difficult task as the entire display has to be removed in order to get at the inside of the machine.

    Something else that can cause shutdowns is overheating. If for example, the CPU fan in your iMac should quit, the machine would shut down rather quickly to avoid damage.

  5. #5
    iMac random shutdown

    Member Since
    Oct 26, 2012
    Posts
    9
    Good call. It coud be the fan.

    But then again, that doesn't quite explain why it would shutdown when attempting to open disk utilties or install a software. I am confused.

  6. #6
    iMac random shutdown

    Member Since
    Oct 26, 2012
    Posts
    9
    Today I tried playing on garageband. Every time I tried to tune my guitar on garageband, the iMac died. Also it died when I attempted to record sound.

  7. #7
    iMac random shutdown
    chscag's Avatar
    Member Since
    Jan 23, 2008
    Location
    Fort Worth, Texas
    Posts
    45,176
    Specs:
    27" iMac i5, 3.2 GHz, iPad 3, iPhone 5c, iPhone 6+, 3 iPods, Yosemite
    I'm beginning to suspect the hard drive along with you. As I stated before, it would be unusual for the drive to cause a shutdown, but I've seen stranger things happen when something goes wrong. Let's check the hard drive:

    Boot the machine with your install DVD and run Disk Utility from the disk. Do a verify and repair run on the hard drive. Also do something else....

    Download the free iStat Pro monitoring program and get a readout on the three fans in your iMac and the temps.

  8. #8
    iMac random shutdown

    Member Since
    Oct 26, 2012
    Posts
    9
    Thanks Chscag. Following is the reading form istat:


    Optical Drive: 799 rpm
    Hard Drive: 1600 rpm
    CPU Fan: 1199 rpm

  9. #9
    iMac random shutdown
    chscag's Avatar
    Member Since
    Jan 23, 2008
    Location
    Fort Worth, Texas
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    45,176
    Specs:
    27" iMac i5, 3.2 GHz, iPad 3, iPhone 5c, iPhone 6+, 3 iPods, Yosemite
    The Optical drive fan looks normal, and the CPU fan is right on the mark. Your hard drive fan though is spinning harder than it should. Normal spin for that fan should be around 1000 to 1100 RPM. That tells us the drive may be running a bit hot or the drive sensor is off somewhat. It could also be that the drive was busy doing something when you got the reading.

    Did you run Disk Utility to verify the hard drive?

  10. #10
    iMac random shutdown

    Member Since
    Oct 26, 2012
    Posts
    9
    Yes I did verify and repair the disk. No problem was detected in either processes. I look forward to getting more suggestions from you.

    Thank you

  11. #11
    iMac random shutdown
    chscag's Avatar
    Member Since
    Jan 23, 2008
    Location
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    Specs:
    27" iMac i5, 3.2 GHz, iPad 3, iPhone 5c, iPhone 6+, 3 iPods, Yosemite
    I'm about out of suggestions. Random shutdowns is unfortunately one of the hardest things to trouble shoot. But we can try one more thing if you have some time to do it:

    Download the free MemTest for Mac program and run it in extended mode. I know it's a "Shot in the Dark" but sometimes bad or intermittent memory can cause reboots and shutdowns. Let's see what it says.

  12. #12
    iMac random shutdown

    Member Since
    Oct 26, 2012
    Posts
    9
    Thanks again Chscag,

    I ran the Memtest and following is the result:

    memtest all

    Memtest version 4.22 (64-bit)
    Copyright (C) 2004 Charles Cazabon
    Copyright (C) 2004-2008 Tony Scaminaci (Macintosh port)
    Licensed under the GNU General Public License version 2 only

    Mac OS X 10.6.8 (10K549) running in multiuser mode
    Memory Page Size: 4096
    System has 2 Intel core(s) with SSE
    Requested memory: 2227MB (2335453184 bytes)
    Available memory: 2227MB (2335453184 bytes)
    Allocated memory: 2227MB (2335453184 bytes) at local address 0x0000000101000000
    Attempting memory lock... locked successfully
    Partitioning memory into 2 comparison buffers...
    Buffer A: 1113MB (1167726592 bytes) starts at local address 0x0000000101000000
    Buffer B: 1113MB (1167726592 bytes) starts at local address 0x00000001469a1800

    Running 1 test sequence... (CTRL-C to quit)

    Test sequence 1 of 1:

    Running tests on full 2227MB region...
    Stuck Address : ok
    Linear PRN : ok
    Running comparison tests using 1113MB buffers...
    Random Value : ok
    Compare XOR : ok
    Compare SUB : ok
    Compare MUL : ok
    Compare DIV : ok
    Compare OR : ok
    Compare AND : ok
    Sequential Increment: ok
    Solid Bits : ok
    Block Sequential : ok
    Checkerboard : ok
    Bit Spread : ok
    Bit Flip : ok
    Walking Ones : ok
    Walking Zeroes : ok

    All tests passed! Execution time: 1900 seconds.


    System Profiler shows 4GB 1067 MHz DDR3 RAMS.

  13. #13
    iMac random shutdown
    chscag's Avatar
    Member Since
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    Specs:
    27" iMac i5, 3.2 GHz, iPad 3, iPhone 5c, iPhone 6+, 3 iPods, Yosemite
    Looks like the memory is good. Like I said above, I'm out of suggestions... If I can come up with anything that may shed some light on the problem, I'll post back to this same thread. In the meantime maybe someone else has some ideas that may help. You might also post this same problem on the Apple Users Community Forums in their iMac section. Some pretty sharp guys hang out there.

    Here's the LINK.

  14. #14
    iMac random shutdown

    Member Since
    Oct 26, 2012
    Posts
    9
    Thanks chscag for making me more aware of the problem. I will stay tuned.

  15. #15
    iMac random shutdown

    Member Since
    Jan 16, 2013
    Posts
    1
    Unhappy imac shutdowns
    As you can tell by my username I have been experiencing this problem for some time now. I have tried everything you have done. I even replaced the PSU and removed fans to clean them, checked the MLB for capacitor blisters and checked all the heat sensors. My problem started about 7 months ago (iMac 24, early 2009). Shutdowns at first occurred infrequently and usually when I was clicking on something in Chrome. Now the problem is occurring about a dozen times a day, even when I'm not engaging the CPU. It happens when the iMac is cold but more so when temps are up (never over 50 C). I am currently operating from an external HD, with the same problem, so it's not the internal HD.

    I am retired with a lot of time on my hands and I've spent well over a hundred hours trying to resolve the problem. Apple is hiding something from us. There are too many iMacs out there (2006 to 2012) that are experiencing this same shutdown problem. I'm sure you've read many of the discussion threads too.

    I will keep trying to pinpoint the problem. Based on the specific details of my shutdowns, I am now suspecting the video card (mine is not built into the MLB). I'll post again when I narrow down cause to this frustrating (and time-consuming) problem.

    Best of luck.

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