iMac Random Shutdown

It's possible that there is a defective memory module that only occasionally fails, thus causing the random shutdowns. However, tracking that down through tests is almost impossible. Replacing the memory modules is usually a more reliable solution.

It sounds to me like the Apple Store has stepped up to the plate. They are doing what's required. Testing your hardware in search of a cause, but so far nothing has shown up. If you were on their side of this what would your conclusion be?

These instructions must be carried out as an administrator. If you have only one user account, you are the administrator.

This procedure is a diagnostic test. It makes no changes to your data.

Please triple-click anywhere in the line below on this page to select it:

syslog -k Sender kernel -k Message CSeq 'n Cause: -' | tail | awk '/:/{$4=""; print}' | pbcopy

Copy the selected text to the Clipboard by pressing the key combination command-C.

Launch the built-in Terminal application in any of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad. Click Utilities, then Terminal in the icon grid.

Paste into the Terminal window by pressing the key combination command-V. I've tested these instructions only with the Safari web browser. If you use another browser, you may have to press the return key after pasting.

Wait for a new line ending in a dollar sign ($) to appear below what you entered.

The output of the command will be automatically copied to the Clipboard. If the command produced no output, the Clipboard will be empty. Paste into a reply to this message.

The Terminal window doesn't show the output. Please don't copy anything from there.

Whenever an anonymous stranger asks you to execute commands in Terminal you should be very wary, Terminal is an effective attack vector, if used with malicious intent or insufficient knowledge it can cripple your Mac. If you do not understand what the code to be entered does then do not enter it. Ensure that that the person who posts it leaves a method of contact for you to use in the event that something goes wrong, and always backup your Mac before executing the code that is posted.

Thanks for the advice

That's not advice.

But it's your advice or don't you recognize your own writing?

After it restarts, does a dialog box resembling the following appear?

• If it does, click the Report... button, copy the entire text of the report, and paste it in a reply.
• If it does not, read the following:

Find the Console app - it is in your Utilities folder and looks like this

You can find it by selecting Utilities from the Finder's Go menu.

Open Console.

If the log list column on the left is not already displayed, show the log list by selecting Show Log List from Console's View menu. Click the "reveal triangles" adjacent to User Diagnostic Reports and System Diagnostic Reports.

Select the most recent crash or kernel panic report. They have names ending in .crash or .panic, respectively. Copy and Paste the text of the report in a reply to this discussion.

Most of the entries will be cryptic but will contain information you might consider personal such as your Mac's name. If you do not want that information to appear, delete or obscure it when posting your reply. Leave enough information so that the entries can be deciphered.

I have the exact same problem with five trips to the Apple Store and they cannot reproduce the problem. I have been advised on this same forum that it is either a bad power supply or logic board. I did not purchase apple care so I cannot get repair paid for. I am right with you in being totally disgusted with Apple service and support. I think there are many others with the same problem, I have seen this on the forums. If you find a solution let me know.