iMac 24inch alu shutting down for no reasons

Discussion in 'iMac' started by virusbeatbox, Feb 4, 2013.

  1. macrumors newbie

    Sep 3, 2012

    I've been having this problem with my 3.5 year old 24-inch aluminum 3.06ghz iMac quite some time now. I have asked this question at 4-5 other Mac/Apple specialized websites but NONE has ever given me a solution or even an answer of what the problem might be.

    The problem is that, when my iMac is booted up for 5-10mins without performing heavy duty, it shuts itself down without any warning or message. It looks like the power cable gets pulled out. I've done a million things already, I'll list them here for the easy of reading:

    - Formatted HDD
    - Full new install of OS X
    - Bought new RAM and replaced them with the old ones
    - PRAM, NVRAM,...
    - Ran Apple Hardware Test many times for hours without any message saying there is a hardware problem
    - Tested the PSU with a multimeter but everything OK

    Noticed that the LED diagnostic leds were burning so I searched the meaning of each light. At iFixit I found out that the fourth led indicates that there is a heat issue. I used compressed air to dust out the iMac and the fans but there wasn'te even any small dust particle in there. I also installed Hardware Monitor to see the temperatures and i saw the Heatsink and GPU was around 70°C before it shutter down.

    So I bought cooling paste and applied on the CPU as well as on the GPU. Then i booted up, saw the 4 leds still were burning. I ran Hardware Monitor to see what the temperature was. All was under or around 20° Celcius and the Heatsink was around 50° Celcius (what i think is a great improvement since previous).
    Still it fell off just like before.

    I really don't have any clue what the problem could be. Could someone please give me some advice to try things? Thanks in advance!!
  2. macrumors 68020


    Aug 13, 2011
    This might be something that you might have tried but didn't list. Do you have the iMac plugged directly into a grounded wall outlet or is it plugged into a power strip/surge protector? Because it doesn't sound like you have any major problems and it might just be that your power source has small fluctuations that could be causing this.
  3. macrumors 6502

    Feb 2, 2013
    Could a Terminal command have been entered by someone (such as sudo shutdown -h M)

    What does the Console Log show prior to it shutting down.
  4. thread starter macrumors newbie

    Sep 3, 2012
    Yes indeed I tried this but forgot to list it. The iMac is plugged into a power strip. I tried to put it into a grounded wall outlet without result.

    No one can access my computer so that kind of command could never been entered by someone.

    I was able to get into the console and get the logs. You can find the logs here:

    Thanks already for taking a look at it!
  5. thread starter macrumors newbie

    Sep 3, 2012
    You can find the logs above here.
  6. thread starter macrumors newbie

    Sep 3, 2012
    Could someone please have a look at the logs? I'm really desperate in what the problem is with my mac :confused:
  7. macrumors 601

    Nov 25, 2012
    United States
    It might cost you a little cash but it would be to your advantage to have Apple do a diagnostic since you say you've been having problems for quite some time. It might be something minor but it could be something major. At least they can tell you what's wrong and if it's cost effective to get it repaired.
  8. macrumors 6502

    Feb 2, 2013
    You probably will have to have it checked by Apple or another Authorized Repair Facility because it looks like it's likely a hardware issue, possibly related to your video card. The symptoms seem to indicate an overheat issue.

    Have you run those logs by anyone over at the Apple Support Forums? Sometimes someone over there is able to answer what the shutdown codes refer to as shown in your logs.
  9. macrumors newbie

    Mar 24, 2013
    Problem ever addressed?

    To the OP, did you ever take your imac into the Apple Store for a diagnostic? If so did they find out what might be causing the shut downs.

    I ask only because I am experiencing the same exact issue with my early 2009 alu Imac (I too have tried all the troubleshooting you listed with no luck either). As one poster mentioned, I have a feeling it might be an issue w/ the graphics card.

    Anyways, let me know if you had any more news to report on this issue. Thanks!
  10. macrumors newbie

    Apr 16, 2014
    Same issue

    Having the same problem with my 2011 21.5 iMac. It's not overheating, though. Took it in to the Apple Store and they couldn't find anything wrong with it after running heavy diagnostics. They reinstalled the OS but it's still shutting down randomly.

    I've tried pretty much all the solutions and this seems to be a very common problem for which Apple simply doesn't have the answer. I know many people have taken their machines in several times with no success at solving the issue.

    Now I'm wondering if it's not some sort of power fluctuation at my house and if a new surge protector/ UPS might help. Currently it's just plugged into a surge protector.
  11. macrumors regular

    Nov 8, 2009
    Claims made without perspective (numbers) can prove almost anything. Let's view numbers for your Mac.

    All electronics are happy even when a UPS in battery backup mode outputs the dirtiest power. For example, power from this 120 volt UPS is 200 volt square waves with a spike of up to 270 volts. Is your household power that dirty? Then you must contact the AC power supplier for a serious human safety issue. But even power that dirty is fine for all electronics ... including your Mac.

    What does the power strip do? It ignores all electrical anomalies until voltage exceeds 330 volts. A number provided with every protector that should never be ignored.

    Ideal voltage for any computer is even when incandescent lights dim to 40% intensity. Is your AC voltage dropping that much? If not, voltage is just fine.

    So, moving on. You have an intermittent. Some better diagnostic procedures can identify a complete defect that causes intermittent failure. One simple tool measures voltages from the power supply. That PSU could be 100% defective and still boot and run a Mac. Did they measure those voltages? Or simply run the machine, see no problem, then declare the defective machine as good?

    Heat is another powerful diagnostic. Many blame heat for failures rather than learn why heat identifies defective hardware. Ideal temperatures for any computer is even a room at 100 degrees F. However, if hardware is completely defective, then it will operate at 70 degrees, fail at 100 degrees, and cause intermittent failures at other times. Best analysis executes hardware diagnostics on hardware while operating the computer at that elevated and normal room temperature.

    In one case, I found a defective video interface. Computer and diagnostic works just fine at 70 degrees. The diagnostic failed when room temperature was raised to 90 degrees. Then one video controller memory location failed continuously. Replaced the defect. Never had another problem for years.

    If a room cannot be heated, another proven technique is to heat individual semiconductors with a hair dryer on high heat. Heat that is not harmful to any semiconductors. And can isolate a defect to a specific and defective IC.

    Examples of how to find defects especially when failures occur intermittently. Numbers provided with each technique to find a defect. Numbers separate proven solutions from speculative recommendations.

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