Random iMac 27" 2011 freezes.

[Konzaleso]

So, iMac keeps crashing and freezing.
Most of crashes happen when using Win7 64bit in Bootcamp, sometimes machine freezes to WELCOME text, sometimes it takes 1-2 hours.
I have reinstalled windows, formatted drive, re-made bootcamp partition, used diffremt bootcamp versions and different drivers/updates. Nothing. It still happens.

OsX side crashes are rare, but still there, mostly while watching flash videos on full-screen.

One common thing with these crashes is, that when it happens, iMac starts causing really loud, buzzing sound. And sound comes from speakers, or whatever is plugged into audio-jack at the moment.
And no, its not the normal iMac memory-fail or general failure sound. This sound is slightly different every time, and it comes even if there is no sound playing when crash happens.

So, does anyone have even slightest idea, what could be the problem. Machine is less than month old and I haven't seen crash-free day in past 2 weeks.

Konzaleso

 

[jkmags]

I have 1 question, I see you already looked at the memory but is it the original 4 or have added more? If you added memory to your iMac have you tried removing the added memory and only running with the original 4? If that fixes your issue then try just your new memory in your iMac, it seems our iMacs can be picky with ram and what memory slot they are in when matching pairs.

 

[Konzaleso]

Aye, added 8gb more Ram. I switched cards to different slots while trying to resolve this problem. I'll try removing extra RAM once I get back from work and see if it works.

Konzaleso

 

[leman]

Was it Corsair ValueSelect RAM, by any chance?

I have a very similar problem with my iMac: it freezes randomly, when I play WoW. Same symptoms as in your description. Didn't try it with Windows yet. All memory tests report no errors. I also contacted the AAPL Express Lane and the support guy told me its Blizzard's error when the iMac crashes while using their software (which is honestly a ridiculous answer, because there should be NO hard crashes/freezes, no matter how buggy the client software is. Hard crash always indicates problems in either OS kernel software or the hardware).

I have since then removed the additional RAM and left the machine with the stock 4GB. So far I had no crashes, but I can't say for sure yet, because the problem was so random (sometimes I could run the game for hours before it froze, sometimes it did so after few minutes).

 

[Konzaleso]

Okay, problem seems to be solved. It was RAM after all.
I was using 2x4gb Crucial Kit, removed it and TADAAAH! No freezes.

I'll try with only 1 extra RAM tomorrow, see if it works.

God damnit, give me back my 12gb of RAM

 

[jkmags]

you could try the 8 gig in the top slots and the 4 in the bottom, basically switching the slots. I have heard some success by mixing up the order... or maybe 8 gig more for 16,.. though this would suck if that didnt work.

Im glad you were able to find the cause, random locks can be the hardest to troubleshoot.


John

 

[AppleNewton]

I have tried with the stock memory and additional ram from Corsair and Crucial -- the Corsair ram is NOT valueselect ram.
It is the same in the 15" MacBook Pro and I tried themin both machines. iMac never fails randomly freeze/lock-up forcing a hard shut down with no cursor movement.

Even on the stock Ram it did lock up once or twice. Reloading the OS a few times never resolved it either.
So I'm not sure if its the Hardware or Software. all RAM tests pass, tried the memory in my MBP (Corsair), the ram works great and never experienced crashing at all on the 15" only on the iMac.


Send your bug reports to:
tattoo@apple.com and kevino@apple.com they are currently compiling these lock-up/freeze/crashing issues to determine what the issue or root cause of the problem could be.

 

[Konzaleso]

Installed one 4gb RAM card into iMac today, and got no crashes.
So, problem must be with the dual-channeling or just in the second card, which matters not, 8gb is more than enough for my needs

Problem finally solved. Thanks for all replies Cheers!

Konzaleso