Problem with 16GB on 2010 iMac 27" i5 & i7.

I'm having the same issue. Just throwing in my RAM purchase for another data point. I purchased (4) 4GB SODIMMs for a 16GB upgrade but due to 1 DOA stick, I ran with 8GB for at least a week with no trouble. Here is the RAM:

G.SKILL 4GB 204-Pin DDR3 SO-DIMM DDR3 1333 (PC3 10600) Laptop Memory Model F3-10600CL9S-4GBSQ
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231341

When I put all 4 sticks in, I started getting the random power-off events. Each time I installed the memory, I reset the SMC, PRAM, etc., booted to single-user mode and ran memtestosx until I no longer felt comfortable stressing out my machine. Each time, no problems were found. If heat were an issue, this test would have caused it. Every time I have an event, it seems to just be with normal use (web page browsing, etc.) and not with running VMware, etc. so it doesn't follow memory failure patterns that I have seen in the past.

I'm looking at the list mentioned (Hynix, Micron & Samsung) and wonder if anyone has picked up any more info as to why they work. Is it the chip configuration or something similar causing this?

Again, I may have had a different issue than you, but the OWC RAM I had was Micron. Replacing my system solved the problem, but that is a difficult route to pursue.

Although I could duplicate the issue in the store, the store could not replace the type of machine I had. The online store couldn't find documentation from the store itself, and wanted more tests done. If I didn't return my RAM soon, then I lost the ability to return.

I had one other option because I purchased it through my company's Apple rep. They managed to convince the online store to return it. I had second thoughts about having Apple incur all the trouble, but was relieved when it finally solved my issue.

If I were you, I would go for Samsung memory.

Thanks. After I posted, I went to OWC and purchased 16GB of the Samsung (Apple factory) memory. I'm hoping that this solves my problem. I'm hanging on to my original 2GB Samsung SODIMMs just in case I end up with the 12GB workaround.

Maybe it's due to the fact that the original Apple ram is CL7 while most other 3rd party RAM chips are CL9? I found this on the net:

http://everythingapple.blogspot.com/2009/11/ddr3-1333-mhz-works-in-new-quad-imac s.html

I second the opinion of Den go to OWC I just got 2 of 4gig and left the 2 of 2 gig that came with the imac and the ram is from OWC and it works like a charm I got 12 gigs and its perfect.

your probably not using the ram that is mac specified.

it all depends if your machine is the late 2010 iMac 27 and 21 inch or the Late 2009 iMac 27 inch like mine if you get the wrong specified ram it would not work you have to look at your specs and if it is either late 2009 or july 2010 imac.

I got the NuRam one which they sell its cheaper than their branded OWC and it works perfect on my machine I wanted to post a screen capture but it does not post correctly
/Users/Tony/Desktop/Screen shot 2010-11-28 at 9.26.50 AM.png/Users/Tony/Desktop/Screen shot 2010-11-28 at 9.27.39 AM.png

Bad RAM perhaps?

I upgraded from 2x2GB to 4x4GB OCZ Memory SODIMM DDR3,1333-8GB KIT,
model: OCZ3M13338GK. €153,- per kit.

http://oi55.tinypic.com/261m0pt.jpg

http://oi56.tinypic.com/313hz7t.jpg

ps what is the forum code to show a link as an picture?

I have not bought it yet. Going to buy the quad i7 in the christmas period, hoping for discounts in the Singapore online apple shop. So the RAMs in the link that I have provided would be able to work on the latest imac?

Same problem here with iMac 21" i5 2010.

I had the freezing/blocking/shutdown issue with 2x2 Apple + 4x4 OWC (hynix) = 12Gb
After reading other threads, I removed the Apple RAM, reducing my total RAM to 8Gb, all from OWC. It worked like a charm, never failed for month.

Then I decided to buy the same brand from OWC ( http://eshop.macsales.com/item/Other%20World%20Computing/1333DDR3S08S/) to try to get to 16Gb. I installed it yesterday (01/19/2011), it crashed this morning...

Just a couple of info: OS is up to date, no SSD, no Photoshop. And I cannot reproduce the problem at will... it's always after a while (sometimes several hours, sometimes several days)

I can't bring myself to go to the Genius Bar as I cannot reproduce the issue...
Don't really know what to do at that point.

Seems that only Samsung RAM is valid to use 16 GB.

Other users haven't problem using 2 x 2 GB Samsung (Apple) + 2 x 4 GB of other RAM (OWC, Crucial, etc.) But you have problems with this total amount of 12 GB, isn't it? That's new! What kind of RAM do you have from Apple? Is Samsung? Other? Perhaps this is the problem.

I think the best solution today is to use only Samsung RAM.

The Apple RAM is from Hynix.

Now I need to update my post. I bought a total of 16 GB from OWC (4 x 4 GB) but in two separate purchases. The reference online is the same for both but I realized today that the first batch (2x4 GB) bought in August 2010 is Hynix and the second batch (2x4 GB) bought in January 2011 is ... well I don't know... it says "OHDI2 D9LCK".

State 1: OWC Hynix 2x4 GB + Apple Hynix 2x2 GB= fail
State 2: OWC Hynix 2x4 GB = ok for month
State 3: OWC Hynix 2x4 GB + OWC 01/2011 2x4 GB = fail
State 4: Apple Hynix 2x2 GB + OWC 01/2011 2x4 GB = trying now... will keep you updated!

Darn.. it just crashed this morning 😟
So to recap, here are my results so far:

State 1: OWC Hynix 2x4 GB + Apple Hynix 2x2 GB= fail
State 2: OWC Hynix 2x4 GB = ok for month
State 3: OWC Hynix 2x4 GB + OWC 01/2011 2x4 GB = fail
State 4: Apple Hynix 2x2 GB + OWC 01/2011 2x4 GB = fail

I will contact OWC and try to see if they can exchange the first batch of RAM with a newer one so that I could try a full 16 GB with the exact same type/brand/model of RAM... wish me luck!
To be continued...

@Arno,

Since the problem has been resolved, you need to contact OWC to get the RAM replaced with the revised RAM chips (I would replace all 4 chips with the same new chips since you bought them all from OWC anyway). When I've had to replace RAM with them in the past, I just cross-ship the RAM and have them cover shipping both ways (you might have to ask them to offer that).

Thanks Jeff.C I did just that and OWC sent me an RMA, with a UPS prepaid postage to return the old batch. Once they receive it, they are going to send me a replacement with a newer batch. I must say I'm very impressed with OWC!
As soon as I receive the new ones, I'll post my results here..