27-inch / 27" iMac Random Shut down

SPECS:____________________________________________________________________________
• 27" 2.8 GHz Intel Core i7 / 8gig / 1TB
• OS 10.6.3 (about to update to 10.6.4)
• All firmware updates have been applied according to software update
• 3 external drives: 1-320 gig 800fw / 1-TB USB 2.0 / 1-500gig USB 2.0

INFORMATION:____________________________________________________________________

I've been running with this configuration ( 3 extra drives) since approximately December with no issues. Out of the blue... only running Aperture and Safari - my iMac JUST SHUTS off- WITHOUTwarning. It acted as though I was running a MacBook and the battery going dead/asleep. That's how random and sudden it shut down - NO WARNING. I did have the iMac asleep for about three hours before coming back to it to start working again when it shut down, but it should have even been cool.

I only started reading around on the web to see of other incidents after this random shut down this evening, but I can't find anything specific. I've found A LOT of similar things - all seemingly related to "HEAT."

And heat seems to be a certain issue recently - in the last day or two. Today I noticed my top back side to be hot, which isn't uncommon, however, it became so hot I really wasn't able to keep my hand on the top back. I've also noticed A LOT of spinning beach balls, and lots of processor delay! Heat??

There are NO energy saver pref's set to automatically shut it down. The power was and is firmly set. There are no network settings, nor access to the iMac to have it shut down. It is not shared with anyone on the network.

SUMMARY:___________________________________________________________________________

• Today, I grabbed a couple temp / monitor widgets and am trying to watch the data. All components seem to be at/around/below 140 degrees F with ambient air at 77 degrees. I don't know numbers, but that all seems reasonable.
• Going to update to OS 10.6.4 (doubt that's it!!)
• I'm going to run the hardware test from my disc to see if ANYTHING. 8-p
• AND... I'm going to call Apple to set up a case. It's still full under warranty, and I have 2 more years of AppleCare on it. But there's been too many things pointing to hardware to call this a software issue.

I've dodged all the display issues with my iMac, but now.. I'm a bit hacked knowing how much I spent on this thing, with the initial DELAYS I went through, ordering it before it had even been released!

?? QUESTION ??_____________________________________________________________________

So, has anyone else been having this issue, heard of a solution, seen anything on Apple's website of known issues ??

Barry
( Grumbling bout my Mac)

Which one of twelve??, Mac OS X (10.5.6), ever hear Newton?!! ;-) One of those, too!

Posted on Jun 22, 2010 8:59 PM

534 replies

Tank9

Level 1

0 points

Mar 18, 2011 2:51 AM in response to peterwillem

I sold the original ram.

Mar 18, 2011 8:28 AM in response to Tank9

That is a pity. Maybe you can make a deal with your memory reseller to exchange 2 x 4 G for 2 x2 G.
Better is sell the whole lot and buy Samsung ram if you really need the whole 16 G.

peterwillem

Mar 20, 2011 8:35 AM in response to peterwillem

Well, its just been over a week since I downgraded from 16GB to 12GB. I have 2 x 4GB Mushkin ram in BANK 0/DIMM0 and BANK 1/DIMM0 - then the factory 2 x 2GB Samsung Ram in BANK 0/DIMM1 and BANK 1/DIMM1.

This configuration appear to be stable with no mysterious shut downs. Hopefully, this will continue.

Regards,

Tony

rseijas

Level 2

186 points

Mar 21, 2011 3:00 PM in response to Anthony Godin

It's been a week and a half since my last random shutdown, and I did nothing but re-seat my Crucial RAM. I'm still running all 16GB and I have not shut down my iMac at all. I was ready to pull the trigger on some OWC RAM but I'm holding off for now. So far, so good.

MattOC

Level 1

0 points

Mar 23, 2011 12:04 PM in response to Berry with an A

I had this happen once last week, and now for a second time this week. 27" 2.93 Core i7 .

Funny thing is that its been running fine with same hardware specs (same RAM) since the week after I got it and put in new RAM (been a month now) but now problems out of the blue?

12 GB RAM - built in 4 GB, plus 2x4 GB from Crucial. I'll have to go back and re-read but maybe Crucial RAM is culprit? I did the re-seat and we'll see what happens. Since it goes a week w/out issues, its hard to diagnose.

cgrey001

Level 1

0 points

Mar 23, 2011 4:50 PM in response to MattOC

I upgraded to 16GB of Crucial RAM when I received my iMac at the beginning of March 2011. I have had two random shutdowns while only using Safari. The iMac has been running continuously the whole time. I did a SMC reset after the first shutdown. I just ordered Samsung Memory from OWC per everyone's recommendation. I hope this resolves the problem.

Mar 25, 2011 9:56 AM in response to Dextercitox

I too am having this issue with a 27in iMac 2.8 i5. We have 16GB of 3rd party ram installed by our Apple Dealer. I too am able to reproduce the issue with a 1.5GB Photoshop file in CS5.
Opening the file and transforming one layer by sizing it and dragging it around.
However, I found something interesting. Very Interesting.
In the performance prefs, I had the tile size set to 128k. Changing the tile size to 1024k seems to have removed the issue. I can not get the problem to repeat itself with 1024k tiles. But as soon as I switch back to 128k, BOOM. Instant off shutdown.
To me, this would point to a RAM issue since the block size change would be related to memory allocation. I still have not seen if this will happen with 8GB or 12GB. I'm still in the troubleshooting process. This machine has already been in twice. First time, they found nothing and pointed to a Wacom driver issue. Well, I have removed the Wacom and uninstalled the driver, so it's not that.
Next time it went in, they replaced the power supply. It was making a buzzing sound when the machine was off. That buzzing sounds is a lot quieter and the machine was good for about 2 weeks and then started again. Now that we are able to replicate it, I feel like I am able to say with confidence that it can be tracked down.
I'll post again when I learn more.
-Scott

Mar 25, 2011 11:52 AM in response to Scott Griswold

Just a follow up. I was consistently able to reproduce this problem when running CS5 with 128k tiles. With 1024k tiles set, I was never able to get it to shut down.
I swapped in some OWC brand ram that we have in another i3 iMac which is the same speed. It has 16GB in it now and is running perfectly. NO shutdown so far no matter what I try.
Will hope to get the other ram replaced by our Apple Dealer.
I still think there is something else going on here, as there seems to be a lot of factors at play. But RAM is certainly the most suspect component with this problem.

MattOC

Level 1

0 points

Mar 25, 2011 12:10 PM in response to Scott Griswold

I would love to have a test to make this a reproducable shutdown to test. I'm not sure I understand the 'tiles' - I have CS5 suite - can you tell me where you found that?

Mar 25, 2011 1:02 PM in response to MattOC

If you go to the CS5 preferences and select the performance section. The same place you set the amount of memory that Photoshop uses. On the right side of the window in the History & Caches area, you can get the cache levels and the cache tile size. Switch it from the default 128k to 1024k.
I'm not sure that really fixes the issue, but it certainly seemed to lessen the frequency or avoids it as I was unable to get it to shutdown with it set that way. Swapping the ram out seems to have fixed it for either setting, but will stick with 1024 tiles anyway since it is more efficient for the files we work on.
Best of luck.

Mar 25, 2011 1:19 PM in response to MattOC

Matt,
the way we were able to reproduce it was with a large file with many layers. The file was a CMYK .PSD file with the following dimensions.
48.25x24.25 at 300PPI.
It contained 14 layers. Most contained a small amount of data. Probably an inch or 2 square.
But 2 or 3 of the layers contained larger elements that covered 30-40% of the layer.
In order to reproduce the error, we would click on the large layer, press command-T to free transform
and then start dragging the sizing handles around. We would also reposition the object and then do some more resizing. Doing that for about 30-60 seconds would result in a shutdown.
This would happen with no background applications running. Just photoshop with this one file open.
But again, it only happened with 128k cache tiles. Keep in mind when switching cache tile size, you need to quit and restart PS for the change to take place.
Hope this helps.
-Scott

rseijas

Level 2

186 points

Mar 25, 2011 8:00 PM in response to Tank9

Well, I went a week and a half with no random shutdowns, same old 16GB of Crucial RAM, and then tonight I had two shutdowns within 10 minutes. Safari and Mail.app were the only things I had running. The second time I had an external USB drive mounted, but not the first time. Looks like OWC is getting my order.

Mar 25, 2011 10:21 PM in response to Berry with an A

I have been spending my whole Saturday reading this entire topic...thanks for all the info!! I bought a 27"iMac December 30 2010 and random shut downs began about a month later. I have 16gig of ram (hynix). I did the Apple Hardware Test and this error occurred:
"Alert! Apple Hardware Test has detected an error.
4MEM/9/40000000:0xb731f718"

It has been getting "repaired" over the last 6 working days and the technician seems to be having trouble finding what is wrong with it. He says he has tested the RAM, and that it is fine. Now he says something about replacing the logic board or power supply. We'll see what happens. This really ***, I just wanna get back to making some music! Now I'm stuck with a Macbook for now:(

Mar 26, 2011 2:07 AM in response to stefanbelieves

Now he says something about replacing the logic board or power supply. We'll see what happens.

If you read all the posts/threads about this subject you will notice that this has been done several times before by other Apple repair shops but to no avail.
Only remedy so far is using Samsung ram for 16 G or downgrade to 12 or 14 G.

peterwillem

NBChick

Level 1

10 points

Mar 26, 2011 3:24 AM in response to peterwillem

Even 12 and 14GB doesn't mean it will work. I was using 12 with iRam (Avant) and factory Hynix RAM and it did shut downs.

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27-inch / 27" iMac Random Shut down