Q: 27-inch / 27" iMac Random Shut down

It's not a heat problem. Don't make your Mac more noisy by running higher fan speeds. I've experienced the 16GB problem from within 5 minutes of a cold start.

Ive noticed that 8GB new RAM alone works well and so does adding your factory RAM to this to make 12GB. But its still not perfect. At least 1 shutdown a month.

Interesting observation. Random shut downs 100% of the time when Safari is running and Im actively controlling the magic mouse. Another discussion page had indicated much success running Google Chrome. Hey presto... I havent noticed the problem since.

So Im now happily web browsing / playing Starcraft II for hours on end with 16GB and no issue.

NB - a software update has just been release for Safari. Its too soon to check if they have corrected the problem. Also dont both with the apple hardware test (passes every time) its probably software - a safari / bluetooth controller problem

Add me to the list. My 27" iMac 2.66 i5 with 8GB of RAM randomly dies, but then restarts. Almost always happens while running photoshop, but doesn't always happen while using photoshop. Totally random, and only maybe once or twice a month.

I am confident to say that the new ddr3 1333 16Gb Apple memory by Mushkin (976647A) with Hynix chips are working as they should. After working on After Effects with 72% of the 16Gb used to render three layers of Rotobrushed 1080p AVCHD footage, I can safely say, buy this ram to solve your problem. Plus it's inexpensive now.

Well folks, I have encountered some good news and bad news.

I am one of the people who posted early in the thread - more than a year ago now. A recap: i5 27" iMac, 8GB factory-installed RAM. I was experiencing sudden shutdowns at random times (with various programs, no one app in particular), trouble waking it from sleep, and lockups on some user-initiated shutdowns.

I brought it into the Apple store (reluctantly) and they all seemed to be shooting in the dark. They had the computer for several days, and initially tried to tell me they couldn't replicate the issue (even though the guy taking it in WAS able to replicate the power issues while I was standing there.) I made a stink and they ended up replacing the power supply (661-5468) and an optical data cable (922-9159).

The work definitely improved the situation (or was part of an amazing coincidence), because I didn't see another random shutdown for the past year. I did see some flakiness on user-initiated shutdowns (I'd ask it to shut down, it would seem to be doing so, but then after the desktop disappeared, the blue screen with the rotating clocky thing would just sit with the clocky thing spinning forever.) But no random shutdowns, which is awesome because this is a work machine and I hate losing my work.

Well, today - almost exactly one year later - I was editing an HD clip in Adobe Premiere Pro CS5. I attempted to random-access a video clip in the preview pane and *BAM* the machine went totally dark. Whoa! I was surprised of course, but as soon as I could get the machine back up I made sure to repeat the action to make sure it was repeatable - and yes, it happened the second time too. And the third time. With various video clips, and so on.

Now, I realize Premiere Pro isn't to blame, but it may serve as an interesting diagnostic tool. (Those of you who don't have it, there is a 30-day trial version on Adobe's site.)

Here is a sequence I have found to reliably cause a shutdown in my i5 iMac 27. I know this is really convoluted, but it's the first time I've found one that's 100% repeatable (for me, anyway):

1. Make sure ALL programs are shut down, and all your work is saved. Triple-check, because it's about to go away!!

2. Open Adobe Premiere Pro CS5

3. Create a new project - give it any name

4. For "sequence type", I doubt it matters, but choose HDV/720p25.

5. From the editing workspace, choose "File-Import" and import a high-def MOV video clip (if you don't have any, grab a NASA clip from here: http://www.nasa.gov/multimedia/hd/)

6. Once the clip is imported, drag the clip onto your timeline (the clip should be in the 'project' window in the upper-left.) .. and drop it onto one of the "video" tracks at 0:00

7. In the "sequence preview" pane (upper right), you should now see the first frame of your video clip.

8. At the bottom of this pane, there's a drop-down that sets your zoom ratio. Set it to 75%. A scrollbar should appear just beneath the video frame (and just above the drop-down you used.)

9. Press the "play" button at the base of the preview pane

10a. Bid a quick "nighty-night" to your iMac, and then:

10b. While the clip is playing in the preview window, use the scroll bar I referred to in #8.

(10b is the point where mine shuts down every time.)

On one of the reboots, I was given an error dump. Rather than clutter up the post, I've uploaded the error text to my web site: http://www.zigzaglens.com/imac-crash-dump.html

Would be interested to hear if this is repeatable with any of you, and/or what you think it might mean.

Thanks, and good luck....

I just removed 4 GB & am now running on 12 GB of RAM.  I'm hoping this could solve my problem until I have the money to purchase new Samsung RAM.  I need all of it for editing videos & music.

Hello all,

I'm sad to report that I'm yet another casualty of random shutdowns, here are my details:

Imac 27 i5 with 4gb originally, upgraded to 16gb little over a week ago (purchased ram from crucial)

It didn't happen right away after the upgarde, only the last couple of days, and it doesn't seem to be related to heat. I'm running istat and I set the fan to run at medium, brought the temp down to 35 degrees while idle, then I cranked up photoshop to finish a project I was working on only for the imac to shut down again.

It's funny because it only happened while running Photoshop or any other Adobe suite program, but when I played Bioshock it didn't act up at all, and I had all settings cranked up to max.

There's a gremlin in my mac ,

When I get home I'll contact Apple and see what they can do for me, good think I got the Applecare extended deal, hopefully it pays off now. In the meantime I'll also try removing 4gb and see if the problem persists with 12 and report back if that did the trick...

I think this will be my last time posting on this thread. I use 16Gb Mushkin Apple ram with Hynix chips. Get ram with Hynix chips to solve your random shut down problem.

Sounds promising, since so far you seem to have gone about 3 weeks without incident, but as I mentioned in my post, it took a little while, almost a month before I experienced the shutdowns since upgrading. I've already sent the Crucial RAM back for a refund, but I'd like to be 100% certain before ordering the Mushkin/Hynix RAM. If you do get a random shutdown in the next week or so, it'd be good if you let us know. I'm hopeful that it doesn't happen but I'd rather err on the side of caution.

Tank9

I have the same Mushkin RAM that you started out with S121 976647A  16 GB worth. I'm having the exact same issue with Parallel 6 with Windows 7  (I know don't say it!)  and also using Aperture 3. Shuts down totally, prior to installing this RAM I had 8 GB of Apple (Samsung) without a single crash since last Sept.

Who did you speak with to exchange the memory, was it the resaler or Mushkin?

Summer 2010 iMac i7 16 GB 2 TB

It's not the same Mushkin memory I had in the first place. I talked with Mushkin and the rep said that he has heard of the random shutdown issue with the 2010 iMac. In order to remedy the issue, they are now using Hynix chips. I ordered directly from Mushkin and got an RMA from them. Make sure you leave them a note that you need the ones with Hynix chips just in case when you do an RMA.

I have  pushed my iMac very hard. Before, I couldn't manage with Maya 2011 or After Effects CS5 not shutting down the computer, but now it dosen't.

@DeltaHorse It has already been over a month without incident. I waited a week before posting a message about the RMA 16Gb Mushkin Hynix ram.

Anyone else having success with this specific Mushkin memory: http://www.mushkin.com/Memory/Apple/976647A.aspx

I just had my 5th shutdown, while computer was sitting idle!  (but doing large backup using crashplan, admittedly), and now i'm fed up and wanting to get some resolution. I don't know if Crucial will take back my RAM but at this point I don't care.

I've had the same exact issue that you discribed. I contacted Mushkin, setup an RMA and I just returned the memory. Hopefully they will send  Mushkin Hynix Enhanced 2x4GB ram, I also think they're aware of the issue

with the current Mushkin  S121 976647A memory with the 27" i7 macs.

I had no problems with crashing/shutdowns prior to installing the Mushkin memory. My iMac runs for weeks before a restart or shutdown.

We'll see what happens with the new memory when it get here. 

THANKS Tank9 for your suggestion about the Hynix memory, I did as you said when comunicating with Mushkin

also Mushkin was very easy to deal with. I sent the info on late Saturday and had a response first thing this morning. All I needed to do was email them a copy of the invoice of the purchase. Before I had my coffee I had a response from them with an RMA number, so far very good service from Mushkin