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

Good News.

I installed the Samsung RAM that Apple sent me to replace my malfunctioning RAM on Jul 17. As of Jul 22 my computer is running perfectly. I have not experienced a single black screen shutdown. I've also noticed the fan runs smoother and quieter than before. Ever since the RAM replacement, the machine runs solid regardless the application or OS (I run Bootcamp also). I'll continue to monitor the performance, but initial feedback is replacing the malfunctioning RAM chips with Samsung solved the problem.

I've bought my first Apple iMac in Jan 2011. Now that Apple solved my random black screen shutdowns, I'm fast learning why people who convert to Apple, stay with Apple.

I've been using 16GB of replacement RAM I ordered from Crucial.com and was experiencing the random shutdown issue at least once a week. Even with only Safari and Mail open it would happen. As an interim solution I yanked out 2 of the 4 replacement RAM modules and reinstalled the factory modules, dropping my total RAM back down to 12GB.

2 X 2GB (Factory RAM)

2 X 4GB (Crucial)

No random shutdowns in almost 2 weeks. Honestly, for my purposes the 12GB is plenty (even "overkill"), but I paid for the full 16GB aftermarket RAM and I want to use it. I am contacting Crucial and seeing about returning 2 or the 4 modules I bought. I will then look for two 4GB modules of Samsung RAM to get back to the full 16GB.

Replacement RAM definitely solved my problem. I installed the Samsung RAM on Jul 17 (21 days ago) and have not experienced a SINGLE random black screen shutdown.

You may remember from my previous posts I experienced at least one and often many random black screen shutdowns daily before Apple replaced my RAM.

My machine runs smooth and seems faster. I've also noticed the fan doesn't run as hot or loudly as it used to.

If you experience random black screen shutdowns running 16Gb of RAM and the RAM is not Samsung, replace your RAM with Samsung and it will more than likely solve your problem.

I will be ordering from OWC, who sells Samsung RAM,  as soon as Crucial refunds my money for their faulty RAM.

Looks like Crucial is having issues with ALL their Mac RAM. The MacBook Pro's are having similar issues:

http://forum.crucial.com/t5/Apple-Mac-Memory/bd-p/Apple

Crucial used to be a great resource for upgrading Macs, but now they just can't be trusted. That's sad.

Just picked my iMac up from the apple store where I took it for repair after calling about my ongoing, intermittent shutdown problem. They kept it a week and "cannot duplicate" so did nothing.

Just so you guys with all the fancy configs know, mine is a simple from the factory late 2009 iMac 2.66 Ghz i5 4GB memory, standard install except for Microsoft Office and Finale.  Hooked up to a nice UPS. I am not a power user, and this problem has been plaguing me almost from the start.  Sometimes I'm working on it, sometimes I'm not and suddenly it just shuts down.  I finally decided to confront them about it and got nowhere.  So I really doubt it has anything to do with power use, modified configs, large amounts of ram (mine gets plenty hot with this modest configuration) -- I'm guessing it is a pervasive hardware problem with a standard component.  I'm on extended warrantee, and had been following this thread once in a while to see if any resolution had been achieved.

So I broke down and brought mine in to no avail.  I wonder what will happen when it goes kaput after the extended warrantee runs out?  I've held on to my PC just in case!

Another two weeks have passes since yanking out half the Crucial RAM. Not a single shutdown or hiccup of any kind since then. Pretty obvious where the problem lies! I posted on the Curcial support forums too.

Now I'm just waitng and waiting and waiting for my RMA from Crucial.

My 27" iMac suffered from random shutdowns. Traced it to a faulty power cord.

Just to add to this, I recently upgraded my mid'2010 i3 iMac from it's stock 4GB to 4x4GB of Corsair RAM.. Since the upgrade I'd been suffering a shutdown about once a day.. After reading through this entire thread, I pulled one bank out, and re-installed the factory 2x2GB sticks, so now running with 12GB.. It's been good as gold so far

Hi, I think you shouldn't just reduce the RAM, better put Samsung RAM (the whole 16) if your machine is in waranty Apple should give you 4GB of samsung Ram for free, and you send them back the original one (the other 3 should be samsung also)

I had originally 16 GB i7 27'' and the iMac was shutting down once a week, later once a day, and then every 2 hours. My applestore agreed to send me 16 GB of Samsung (and mail the original back to them) at no cost. Not a single shutdown since then. THIS IS AN ISSUE APPLE SHOULD SOLVE!

I think this is a Crucial issue, not an Apple issue. If the iMacs all function normally with Samsung RAM but gag on Crucial RAM, it's clearly a Crucial issue.

Acturally its Everybodies issue, Its Crucials, OCW, Mushkin, Apple, etc, problem. I am assuming here, but I can only guess that Apple sent the wrong specs over to the ram manufacturers, so they ended up producing ram that causes this issue at 16gb. However what ever the issue was, it has been fixed.  It doesn't matter what brand of ram you have, if you experience this problem, contact the manufacturer of the ram. From this forum, all brands know of the issue and are working with customers to replace the problem ram. Personally I have 16gb of Mushkin, after experienceing this problem, and them sending out replacements I have gone without a signal unexpected shutdown.

So if you have an issue, it takes 5 mins to track down the manufacturers phone number, and about another 5 mins on the phone.

Samsung seems to have gotten it right. Mushkin also seems to have it right. Crucial screwed the pooch though, and OWC is just a reseller, no?

Somebody on the Crucial support forum claims that OSX 10.7 Lion cured this malady. Does anybody have experience with Lion fixing this random shutdown issue with 16MB of RAM installed? Seems hokey to me that someone claims this fixes the problem, but stranger things have happened. Until somebody else confirms this I'm assuming the guy posting on the Crucial site is a plant or a fanboy with an agenda.

Ever since I upgraded from Lion 7.0 to 7.0.1 I've been having shutdown problems again (been running great the past eyar since I installed the Samsung RAM that Apple sent me).

If I remove two sticks (bringing it down to 8GB) it runs fine (just very slow because I run a lot of server development apps).  I'm super-swamped with work, but will be likely brining it in for repair soon.  In another thread a guy seems to ahve the same problem.  They replaced his logic board, but he's still having issues.

...sigh =\