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Late 2015 27" iMac 64GB RAM Problems

Steve Sherrick

Steve Sherrick

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On my iMac 27" I recently started having kernel panics and began the process of checking RAM through Apple diagnostics. Thought I identified a bad module through this process and had OWC replace the "bad" module. The new one they sent seem to flag the Diagnostics as well. So I went through a thorough RAM installation process as this has been known to help when things get quirky like this.

- First I tested each 16GB RAM module. Each one passed diagnostics
- Then I tested each slot with that known good module. Those also passed.
- Then each time I installed a new module, I did an NVRAM reset and a PRAM reset. I would check to make sure the new module showed up in RAM view.
- After all were installed I then ran the Apple Diagnostics again and was presented with the PPM003 memory module error.

OWC has been helpful, but have admitted that they have seen some machines from that late 2015 batch that are quirky with RAM. People send the RAM back and it checks out fine in their test machines.

Wondering if anyone else here has the late 2015 iMac with OWC 64GB RAM upgrade and has run diagnostics to see if it comes up with any issues. Perhaps I got a temperamental iMac.

For anyone with this same config, would love to compare notes.

Here's some other info about my config:
iMac Retina 5K 27" Late 2015
4GH Intel i7
AMD Radeon R9 M395X 4GB
OS 10.11.3


4GH
 
The machine seems to run very smooth with 32GB which Apple Diagnostics passes with no problems. There seems to be something about the combo of 48 or 64GB of RAM with this machine. Very unfortunate. Seems that some run just fine, including the ones they have at OWC.
 
You still under warranty/applecare? Just get the computer replaced/repaired. It's supposed to support 64GB.
 
Same results if you juggle the modules around between the slots? If it works fine with 32GB in there, then you swap those two modules for the other two modules, does it still work fine?

If it works juggling modules around and only errors out with PPM003 with 3 or 4 modules installed, regardless of which one is left out, I'm betting you have a faulty slot. Time to claim on the AppleCare.
 
Jeff, would it be possible for a faulty slot to pass the test when it has a single stick of RAM in there? In other words, can the faulty slot rear its ugly head when more RAM is involved in other slots? I tested each slot with a single stick to see if I could find the bad slot but they all passed and I did that with each stick too and each one passed. It seemed the only way I could make it not pass was exceeding the 32GB.
 
I also have one of the latest retina 27" iMacs (4 GHZ) and it had the same issue. Usually caused during render on some longer length projects. Talked with apple and problem got escalated to their caretaker level support which I think is tier 4. Anyway, long and the short of it was that they said anything more than 32gb wasn't actually supported (I was running 64, then 48, then back to stock 32). Haven't had any panics since going back to 32. Unfortunately for me, I couldn't find a solution that allowed my mac to run 64, and apple wouldn't replace it because anything more than 32 isn't supported by them and I couldn't get the problem to replicate with 32 in the computer..
 
Nevin Thomas said:
I also have one of the latest retina 27" iMacs (4 GHZ) and it had the same issue. Usually caused during render on some longer length projects. Talked with apple and problem got escalated to their caretaker level support which I think is tier 4. Anyway, long and the short of it was that they said anything more than 32gb wasn't actually supported (I was running 64, then 48, then back to stock 32). Haven't had any panics since going back to 32. Unfortunately for me, I couldn't find a solution that allowed my mac to run 64, and apple wouldn't replace it because anything more than 32 isn't supported by them and I couldn't get the problem to replicate with 32 in the computer..
Click to expand...
Interesting, sounds like we may have got slightly different machines than the ones OWC has or ours have strange quirks in the hardware. OWC says there's no reason the iMac can't handle it, at least in theory.
 
Hi Steve,
just came across your post and I am also suffering the same issue you had or are still having with your 64GB OWC memory in your 5k iMac. My specs are the same as yours, a top spec iMac maxed out with 64GB OWC memory. The first batch of memory was fine for 2 months but then the iMac wouldn't boot due to memory error. 3 beeps on startup. This was returned to OWC who replaced it with a new memory set. This 2nd set now has the iMac randomly shutting down without warning and randomly freezing. Mouse cursor moves but nothing is clickable. None of these symptoms are present when I remove the OWC memory and put the 8GB Apple supplied memory back in. At this rate I'll be asking for a refund. Asking for another replacement is time consuming as I'm in the UK, and it takes ages.

I was was wondering if you ever resolved your similar issue, or did you just have to put up with it. Be interesting to know how you got on.

Thanks.
Ian
 
Hi Ian. I had to finally roll back to 32GB and give up on 64GB. If I hadn't been experiencing any peculiar behavior and got those errors in the diagnostics I would probably just write it off as Apple Diagnostics seeing an exceeded spec for that given machine and flagging it. But like you, I had issues that went away when I went back to the approved max amount of RAM. A bit frustrating as OWC says all their machines handle 64GB just fine. You may want to have them look into this further as it's clearly not an isolated incident with my iMac.
 
Thanks Steve, I have flagged it with OWC and await their response. I may have to follow your example and remove two of the 16GB modules to see if it sorts iselft out. Not ideal though.
 
Ian, I'd be curious if this solves it for you. If it does, then that means that either some of the Late 2015 iMacs are different in some way or there's an issue on the OWC side.
 
Hi, Steve
I have same 64gb RAM issue in my iMac 2015 late i7-4ghz 512gSSD AMD M390 2GB
but my situation is very strange cause all Ram module are passed the Apple diagnostic
Imac will automatically reboot after over night sleeping or reboot unexpectedly when play video in youtube
I restore all the system but it always reboot unexpectedly even I swap all RAM module in different slot.
if you got some solution , please post

Gary
 
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