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Old Feb 7, 2013, 11:50 PM   #1
The Monkey
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New 27" iMac RAM Problem - won't recognize more than 16GB

I got my late 2012 27" iMac with 8GB RAM. I purchased 16GB of the recommended Crucial RAM (using the Crucial configurator). After installing the RAM with the Apple RAM, 24GB appeared in system information. However, after shutting down and restarting from a cold boot, it only reported 16GB. After playing around with the slots a bit, I could get it to recognize any 2 RAM chips, but never all 4.

So I figured the brands weren't getting along. Ordered 16GB more of the Crucial RAM and same thing is happening. It won't recognize more than 2 RAM chips. The weird thing is that it is not isolated to one slot. Each slot seems capable of recognizing the RAM, but once more than 2 are populated, only 2 are recognized and the other 2 are reporting empty. I have repeatedly tried to make sure they are seated right, and am now running out of ideas other than I may have a hardware issue. The only thing that is keeping me very slightly optimistic is that each port seems to be functional, just not all at the same time. Maybe I'm doing something wrong.

ANY HELP WOULD BE GREATLY APPRECIATED.

The Crucial RAM is model # CT2C8G3S160BM

The iMac is a 3.4 GHz i7.

Last edited by The Monkey; Feb 22, 2013 at 08:21 PM. Reason: ssspellling
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Old Feb 8, 2013, 12:05 AM   #2
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That seems odd. I bought the same 16gigs of RAM and installed it with the factory 8 and have not had a single issue. I swapped locations of the factory RAM so the crucial sticks are first. Did you make sure all the sticks are seated firmly? I seem to remember that it took some effort to push them into their seat. I also did notice that the pairings are staggered, so check to see if you have matched pairs in "About This Mac" It'll show you clearly how the sticks are installed. I have read that these computers are not happy with unmatched pairs of RAM sticks. If everything looks happy, you might have some hardware issues, and despite having aftermarket RAM, Apple should take care of it.
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Old Feb 8, 2013, 12:16 AM   #3
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I agree it's really odd. I'm going to try to seat them once again as I know that is really the most common problem. Any tricks? These seem a little finicky about seating (i.e., they seem to be in but maybe aren't). Sometimes I don't hear an audible "cick," they just sort of slide in, but seem to be trued up. Very frustrating.
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Old Feb 8, 2013, 01:39 AM   #4
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Well, simplest first. I've tried enough reseating etc. for now. Always possible I got bad RAM so I ordered another 16GB kit. We'll see. But I also tried putting the original 4GB chips back in with the Crucial RAM and they weren't recognized.

Not fun.
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Old Feb 8, 2013, 02:27 AM   #5
BigMac25
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Ordered crucial 32gb of ram from newegg, no problems installing and recognizing all the ram. I would have apple check it out.
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Old Feb 8, 2013, 02:28 AM   #6
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Originally Posted by BigMac25 View Post
Ordered crucial 32gb of ram from newegg, no problems installing and recognizing all the ram. I would have apple check it out.
My guess is you're right. Such a PITA, but first world problems and such...
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Old Feb 8, 2013, 04:45 AM   #7
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Why didn't you just get 32? it's under 200$.
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Old Feb 8, 2013, 06:42 AM   #8
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Why didn't you just get 32? it's under 200$.
Helpful.
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Old Feb 8, 2013, 07:42 AM   #9
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Have you tried a PRAM and/or SMC reset?
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Old Feb 8, 2013, 07:57 AM   #10
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Yes, thanks, both. But I'm going to try again today. It's weird; almost as if whatever the BIOS equivalent is is limiting total RAM to 16GB. Of course, it could very easily just be hardware failure.

Is there any way to find out if the max RAM has somehow been limited?
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Old Feb 8, 2013, 08:44 AM   #11
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Originally Posted by daneoni View Post
Have you tried a PRAM and/or SMC reset?
Further to this, I flushed the PRAM but only once. Crucial email support just recommended doing it 3 times, so I will do that later today.
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Old Feb 8, 2013, 10:22 AM   #12
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How did you come up with that RAM model? When I check Crucial's configurator for a 2 x 8GB (16GB) kit for the late 2012 27" iMac, I get part # CT3650282. In fact, Crucial didn't recognize the part number you quoted when I did a search on their site.

This is the page that shows the compatible memory:

http://www.crucial.com/store/listpar...%20Late%202012)

Are both sets of Crucial RAM producing the same effect when installed with the original Apple RAM? In System profiler, do the same sockets always show as filled and empty, or does that change each time you swap the DIMMs?
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Old Feb 8, 2013, 10:28 AM   #13
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How did you come up with that RAM model? When I check Crucial's configurator for a 2 x 8GB (16GB) kit for the late 2012 27" iMac, I get part # CT3650282. In fact, Crucial didn't recognize the part number you quoted when I did a search on their site.

This is the page that shows the compatible memory:

http://www.crucial.com/store/listpar...%20Late%202012)

Are both sets of Crucial RAM producing the same effect when installed with the original Apple RAM? In System profiler, do the same sockets always show as filled and empty, or does that change each time you swap the DIMMs?
The Crucial model numbering system is a mess. I believe the part # you show is actually the same part, but Crucial uses certain of its part #s to link to certain machine usage for problem tracking etc. This is what I've gleaned from the Crucial website. But it is certainly far from clear and easy. Regardless, I used Crucial to configure the chips and the part number I gave above is the one that I received. I then ordered the exact same from Amazon. I just did it again through Crucial, and the part # was the one you showed above.

And I can find no consistency with respect to the problem. When all are filled, it appears that DIMM0 is always shown empty. But if I just fill those, leaving the others truly empty, then everything works fine. I need to make a more organized sheet of my trial and error, though. Maybe some pattern will emerge.

And both sets of RAM appear to be producing the same effect, but I will confirm that again just to be certain.

EDIT: For those interested, here's a thread over at Crucial's forums that explains the reason for different part #s for the same memory: http://forum.crucial.com/t5/Apple-Ma...es/td-p/111512

Last edited by The Monkey; Feb 8, 2013 at 10:35 AM.
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Old Feb 8, 2013, 01:47 PM   #14
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Hopefully you are not that far from an Apple store. If so, I would perform the SMC reset and flush the PRAM, maybe more than once.

Place the factory RAM into the iMac, check that it is in the original slots 0, 2.

Take the unit to the Genius Bar and have them install the 32GB of memory and witness this issue. I think that there is a failed part in your iMac.

If you're not close to a B&M store, I'm afraid that you're looking at a return/exchange.
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Old Feb 8, 2013, 02:34 PM   #15
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Thanks for the advice. I'm afraid you're right. The thing to do is bring it in. I'm in NYC, so it's not a big deal, though inconvenient.

On a side note, if you purchased a unit at an Apple store, can you exchange it at a different Apple store?
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Old Feb 8, 2013, 03:21 PM   #16
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The memory controller is in the CPU chip. There are no active components between the RAM sockets and CPU, only the circuit traces. The fact that all four sockets work in pairs indicates there are no physical connection issues between the sockets and the memory controller logic for each socket.

It looks to me that that the memory controller is having an issue with that particular Crucial RAM. It could be a problem with the internal organization of the chips on each module, i.e., two physical DIMMs can look like four modules. It could also be an issue with the memory loading, and the memory controller not being able to handle four DIMMs, which would indicate a defective CPU. A quick look at the Intel communities indicates that the 3770 CPU memory controller can have issues with particular memory modules and memory socket configurations. The 3770 can handle both 1.35v and 1.50v RAM.

If you could get a couple of Apple DDR3 SODIMMs to install with the original ones, even from an MBP, it would settle the loading question.
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Old Feb 8, 2013, 03:23 PM   #17
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good advice, thanks.
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Old Feb 13, 2013, 01:21 AM   #18
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Just an update. Got 2 new sticks from Crucial. Same problem. Time to go to the Store I guess.
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Old Feb 13, 2013, 01:33 AM   #19
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Quote:
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Just an update. Got 2 new sticks from Crucial. Same problem. Time to go to the Store I guess.
Yup - how old is the machine (Within the 14 day exchange period?)? They'll run the AHT, and see what's wrong. I hope you get a replacement on the spot; and TBH, you should be pushing for one. 32GB is supported.
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Old Feb 13, 2013, 01:52 AM   #20
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Took delivery about a month ago.

----------

I guess my other question here is do I call AppleCare first or just bring it to the store? I have the big SSD so I doubt they'll just be able to do a swap.
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Old Feb 13, 2013, 01:56 AM   #21
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Took delivery about a month ago.

----------

I guess my other question here is do I call AppleCare first or just bring it to the store? I have the big SSD so I doubt they'll just be able to do a swap.
Oh it's a CTO? You should make a genius appointment for an exact time, take it in, then yes they can't replace CTO right there and then. Given the supply constraints, you'd have to wait however long the wait time is (few weeks?)
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Old Feb 20, 2013, 11:11 PM   #22
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Just an update. Went to the Genius bar and replicated the problem. But of course they had no Apple-certified RAM in house so we reached an impasse as to whether it was the Crucial memory or the logic board or something else. So I bought some more Apple RAM, popped it in, same problem. I'm going to call AppleCare and try to get them to replace the machine.

This stinks.
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Old Feb 21, 2013, 12:57 PM   #23
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What does Apple Hardware Test say?
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Old Feb 21, 2013, 01:19 PM   #24
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Thanks for the link. Will run it tonight and report back. It passed using Apple RAM only (and only in 2 slots) at the Apple Store and ran into a problem running (I think) when loaded up with the Crucial RAM, but this of course gets back to the third party out for them.
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Old Feb 21, 2013, 11:48 PM   #25
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What does Apple Hardware Test say?

Hmm. Not good. Seems to be hanging at probing hardware.
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