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

Actually, what I have seen so far is three different kinds of causes to the sudden shutdown syndrome.

1 - incompatible RAM with 16GB installed. Reducing to a total 14GB helped.

2 - Bad power supply - often accompanied by faint sparkling noise - replacing power supply helped.

3 - iMac with unknown problem as the one I am currently sitting in front of. I have replaced the logicboard, the power supply, the harddisk, the ram and nothing so far has eliminated the cause.

Even worse, I CAN make it shutdown when I open iTunes and browse around (without even playing a song). It shuts down every time. It also does this on a clean system with just a few songs imported freshly from CD.

The console/log attribute "previous shutdown cause" always is -128, which means the SMC doesnt know why it shut down.

I am pressing apple to take the imac back for refund as no one seems to be able to find a fix.

I think I would be having Apple replace that iMac, unfortunately it sounds like a Monday Mac. You really have nothing left to replace!  I went through two sets of memory before this one worked  fine, this was of no fault of Apple though, just bad chips on the memory stick. Mushkin was able to resolve the issue.

Good luck with getting Apple to exchange,  hopefully you have warranty or extended warranty.

Just to add my own confusion to the issue - got 2 i7 iMacs one of them has the shutdown problem and the other one doesn't.  Both have 16GB Crucial memory which I have tried in all the possible combinations and the iMac that shuts down still does with the other being unaffected.  Both are run on APC UPSs (power here in Spain is not the best I have ever encountered).  The offending iMac has been to the local Apple agent and they weren't able to reproduce the problem so I am now starting the process with Apple for a warranty replacement/repair (don't care which).

Irritatingly the iMac that doesn't shut down is now with Apple because it has the wobbly screen/hangs on screen-saver problem.

Just wanted to report that I've had no problems so far with the ram I purchased from macsales.com. So it looks like OWC and Mushkin are the safe bets here, although it seems evident from the last poster's comments that the issue isn't necessarily related to the brand of third party RAM used. In any case, I'm glad to finally have the full 16GB upgrade without the hassle. Good thing about macsales.com is they deliver internationally and their customer service is very good.

I've been running with 16 GB for about a month now, with no random shutdowns. I have manually done a few shutdowns my self, but so far I have not ran into any issue.. So it seams the solution to this 16gb issue, is Either it has to be samsung, or Hynix branded chips (Which Mushkin and OCW i believe uses).  I would contact Crucial and talk with them, since it sounds like you just need to get replacement ram.

All 8 modules work perfectly in any combination for one of the iMacs so for me at least it may well not be a memory related problem.

Dear all,

I have an iMac 27" i7 16GB Ram, same problem of shutting down.

I have been using USB keyboard+mouse (bluetooth off) for a while and the problem persisted, even increased in frequency.

The shop where I got the iMac agreed to mail me SAMSUNG memory then I mailed the defective back to them.

Since then everything is running good, no shut downs anymore!

I have yet to have a shut down since taking out a memory stick in late April, about 2 & 1/2 months.  This confirms to me that it is indeed the RAM.  Looking to purchase more now.

I have a question.  I have OWC RAM in my Mac, which supposedly has a warranty.  How can I go about replacing that RAM?  I don't think I should have to pay another $200 bucks for something that shouldn't have been a problem to begin with.

Well from what I could see on their website, the ram has a lifetime warranty on it. So If you are having this problem, I would just call them up, explain the problem your having and state that you would like to return the defective ram for the new stuff. At most you might just have to pay shipping to ship your defective ram back to them.

if your mac is still on warranty you should not pay anything, the shop where you got it should give you new RAM (I got Samsung) for your computer. it'll take 5 minutes to replace it.

BTW, apple should change all the defective Rams are around, as they did with the G4 ibook batteries some years ago that they were getting fire spontaneously.

I'm disappointed to report I too added my name to the list in hopes if enough of us complained, Apple would correct the problem.

Like others, I experience random shutdowns regardless of application in Mac or Windows (Bootcamp) and independent of memory configuration. Shutdowns are more common on Windows when I run my CAD program, but still occur randomly and frequently on the Mac side.

I bought my maching Dec 2010 and experienced random shutdowns the first day and at least once/day everday since. This is a rude awakening for a 20-year windows veteran who decided to convert to Mac.

One thing I've noticed is after each random shutdown, I am able to reboot easily and immediately. If I re-open the application(s) I opened before the crash, the Mac mysteriously remembers where I was (all applications) even if I was logged in to a webpage.

I use a USB Passport for backup (to share files with my Windows side). After a random shutdown, the drive disappears and it takes a couple minutes for the iMac to find it again.

I'm severely disappointed in my new and expensive iMac (still paying for it) and patiently await a solution.

Here are my system specs.

Model Name:    iMac

  Model Identifier:    iMac11,3

  Processor Name:    Intel Core i7

  Processor Speed:    2.93 GHz

  Number Of Processors:    1

  Total Number Of Cores:    4

  L2 Cache (per core):    256 KB

  L3 Cache:    8 MB

  Memory:    16 GB

  Processor Interconnect Speed:    4.8 GT/s

  Boot ROM Version:    IM112.0057.B00

  SMC Version (system):    1.59f2

How did you get 16 GB of ram. Did you add it yourself, or was it apple provided? If you added it yourself, what was the brand? And like many of us, If you added it yourself, Call up the manufacture (OCW, Mushkin for example). Explain the problem your having and they should be able to send you ram that wont cause the shutdown.

If the ram was apple provided, I would contact apple and mention the problem (and this disscussion), chances are they probably will just swap out the ram.

It would be nice to know who's at fault. Is it the manufacture's, trying to create cheap ram? Or Did apple give faulty information? At least at the moment there does seam to be a fix, its just a matter of getting the defective ram off the 'shelves'...

I've installed 16 GB Mushkin Hynix memory, been running for over a month now, (installed around 3rd June)

The only restart is to install updates. I've had this computer for almost 1 year, purchased on-line 18 Aug. I have not had a single issue except for the memory which is really no fault of Apple or Mushkin. Mushkin was quick to resolve the issue, it took two shipments of memory but in the end I was happy with the service.

If your computer(s) are having issue with the memory that shipped WITH IT then you need to contact Apple directly. Memory can go bad, i.e. power serge, faulty components. Please keep in mind that Apple has fewer faulty components and a higher standard then the industry norm.  This is why we pay more, if you would like a $500 computer then by a Dell or other crap from the big box stores. I've been working in this industry for the past 16 years, done warranty repair for Apple, HP, Compaq, Dell, Motorola, the best is Apple! Sure they're not without

fault but they are better then $500 boat anchors.

The 16GB of RAM came with the computer I ordered. I did not install it myself, but I remember when I first received the machine it only showed 8GB even though 16GB was installed. I called tech support who talked me through reseating the RAM. After reseating the RAM, they system showed 16GB and later that day, I experienced the first random black screen shutdown.

Upon the members in this forums advice, I contacted Apple and they sent me replacement RAM (Samsung) which I installed today. I'll test the computer to see if it sustains. As I reported previously, I experienced multiple random black screen shutdowns daily. I'm hopeful the new and more compatible RAM will alleviate the problems.

I'll report back periodically.