Model A1225 / Early 2009 / 2.66, 2.93, or 3.06 GHz Core 2 Duo processor

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Why is my iMac randomly shutting down?

imac early 2009 os x 10.7.5 previous shutdown -128

I've done SMC reset several times. Checked temp. Problem is intermittent which is to say, I can't create the conditions for it to shutdown. Always get the same message Previous Shutdown -128. Can't find any code list; so I don't know what -128 means. What could be wrong?

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Can you give us the exact error message besides the code. Sometimes its an app Vs the OS that is to blame here.

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Also can you give us the last three digits of your serial number so we can correctly identify your system.

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iMac "Core 2 Duo" 2.93 24-Inch (Early 2009) A1225

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Which ever apps are open at the time of crash may be the cause. WIth strange behavior the preferred method of software troubleshooting is to delete the .plist files. They are all found in ~/Library/Preferences. You can put them all in the trash, restart then delete them. Of course you'll have to reset all your preferences.

Another cause could be a failing HD. Run Applications/Utilities/Disk Tools:Disk First aid verify disk and repair permissions. If errors are found in the HD you'll have to boot to your repair partition and see if you can fix them… if not you'll need a new HD.

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Yes. Last four of serial: 30TL

Exact message: kernel: Previous Shutdown Cause -128

Every time it happens.

Hey this is excellent information that I was not able to find anywhere else.

I'm gonna follow your suggestions and see how it goes.

Thanks a million.

Cheshire

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Have you added any 3rd party RAM? Can you put the old RAM back and run it for a bit to see if the shutdowns stop?

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Run AHT in extended mode - if it finds no errors from one run do tow more back to back (sometimes -especially if it's an overheat problem one run of AHT is not enough "use" to cause a problem).

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Try running it in Safe Mode (boot with Shift key pressed until the progress bar comes up - about 30 seconds). You will have 'Safe Mode' in red top left of screen if successful.

Is the the iMac now stable? If so, your problem may the same as mine appears to be ie an over-heating GPU (graphics processor unit - video card). To test this, install smcFancontrol which allows you to speed up the CPU/GPU fan (it is shared by both) and see if the extra cooling stops the shutdowns.

The other thing you could try is to disable Quartz Extreme which is OSX's graphics accelerator software. This is for when running in normal mode. My theory is that because QE is disabled in Safe Mode, the GPU does not work anything like as hard as when QE is running and so does not overheat so no shutdowns.

I am about to try these on my iMac and will report back... MW

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