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10900K iMac Crashes Frequently

I also have an OWC RAM kit for my Early 2008 MacPro (which I'm still using :P). One pair of the RAM sticks caused an issue with a blank screen on startup and flashing power light. I removed the RAM pairs one by one to find the offending set, and ever since I took it out the computer has been OK. I even got a replacement for those faulty RAM sticks from OWC under warranty, but after a few weeks the computer started showing errors again until I took the new sticks out. I basically just left them out from that time on, as I'm not sure if it's the OWC RAM causing the issue or those specific RAM slots or something else. Basically I've just been living with a bit less RAM in this machine rather than fight it.
 
Given what OWC told you, I'd try getting them to replace some or all of the RAM you have. If you don't get a set that works properly, eventually they'll have to refund you.

Also, it appears that B&H has Crucial RAM in stock - https://www.bhphotovideo.com/c/product/1600342-REG/crucial_ct2k32g4sfd8266_2_32gb_ddr4_2666_sodimm_1_2v.html (here's a 2x32GB kit).
 
This sounds like a hardware defect.

I have a couple of self-built PCs that never crash. I also have a few Macs (including a 2019 Mac Pro) that never crash. You shouldn’t have to put up with this.

Back in the day, I had a MacBook Pro that *did* consistently crash. Apple couldn’t find anything wrong with it. I had to be very persistent for them to give me a new one. My advice is don’t back down.
 
Thanks everyone. I'm going to go through the replacement song and dance once more with OWC. I'll try to get onto level 2 support with Apple as well.

@Symfoniq - my last computer was a PC I built myself that never crashed, so you can imagine my chagrin about this going on for so long without a resolution!
 
I feel for you going through this - really shouldn't happen. I had a bad OWC stick several years ago - I think it was with the original 2009 27" iMac. They sent a replacement very quickly and it worked fine after.

At the very least, if another set from OWC doesn't fix the problem, you'll have more data to give to Apple and hopefully get to the bottom of things that way.
 
Have you run the memory diagnostics yourself?

If you hold down D (might have to use a wired keyboard) on restart you’ll get to Diagnostics and can run the memory test from there.

You could also test the RAM with Rember:
I've run Rember maybe 10-15 times, mostly on the different sets of OWC RAM which sometimes passed and sometimes failed, and a handful of times with the Timetec RAM which always passed.
 
Sorry to bump this, but the saga continues...

I took the iMac in to the Genius Bar a few weeks ago and left it overnight. They ran their diagnostics and told me the only failing component was the RAM (my 128 GB OWC kit.) I ordered another brand of RAM from Amazon (Timetec) and it seemed to resolve the problem for about a week, but then I got a couple kernel panics with it installed. OWC support won't let me return the RAM I bought from them, saying "under Magnuson-Moss Warranty Act the memory would have to be replaced three times for the same issue before it could be deemed a lemon and a refund offered." So they are putting me through the same series of troubleshooting steps I went through with them before I took it to the Apple Store. The latest was to restore some disk permissions via the internet recovery option. I did that with the Timetec RAM installed and it was okay today.

Tonight when I tried to reinstall my four OWC DIMMs (so I can return the Timetec kit) the computer wouldn't boot. I tried several combinations of slots and eventually got it to boot with only the second from the top slot and the bottom slot installed. When I tried all four DIMMs again it wouldn't boot, so I went back to the two slots mentioned above. It wouldn't boot on the first try, but I fiddled with them and it eventually booted, so at the moment I'm only running with 64GB installed.

Needless to say I'm very frustrated and wondering if I should figure out a way to cut my losses and get rid of this computer. It seems to me that there might be some bad RAM slots. Maybe I can get Apple to replace it, but at this point I feel like nobody can help me get to the bottom of this. Apple blames OWC, OWC blames Apple...

Suggestions welcome.
This sounds almost identical to what a friend of mine went through. In the end we -mostly- solved it by replacing a single stick of the OWC RAM... and found the unfriendly stick through rigorous testing on multiple combinations of the sticks, just like you did. Apple support was basically useless and suggested pretty much everything except for this (nothing worked that they suggested). the system is much more stable now after replacing that one stick (keep in mind all the RAM passed diagnostics)... the system is not perfect though and still has a kernel panic every now and then. But before it was panicking anywhere from every 5 to 30 minutes at times. I think some of these machines are just not too friendly with maxed out with OWC / 3rd party, or there is a defect with the slots that causes these problems with certain sticks of RAM. hard to say! Having seen what he went through I would probably tell people to avoid this particular iMac.
 
I thought memory had to be installed in matched pairs though. I didn’t think it was wise to mix and match different manufacturers’ sticks together.

I really hope you get it sorted. I can imagine this sort of thing is enough to put you off Macs for life.
 
This sounds almost identical to what a friend of mine went through. In the end we -mostly- solved it by replacing a single stick of the OWC RAM... and found the unfriendly stick through rigorous testing on multiple combinations of the sticks, just like you did. Apple support was basically useless and suggested pretty much everything except for this (nothing worked that they suggested). the system is much more stable now after replacing that one stick (keep in mind all the RAM passed diagnostics)... the system is not perfect though and still has a kernel panic every now and then. But before it was panicking anywhere from every 5 to 30 minutes at times. I think some of these machines are just not too friendly with maxed out with OWC / 3rd party, or there is a defect with the slots that causes these problems with certain sticks of RAM. hard to say! Having seen what he went through I would probably tell people to avoid this particular iMac.
Thanks for your post. This is my fear — that even if I can get Apple to replace the computer it might not solve the issue entirely. A kernel panic once in a blue moon isn't the end of the world, but it's exactly what you hope to avoid when you pay the premium for a Mac.
 
Mine has been okay since I got the latest round of replacement sticks from OWC about two weeks ago. I'm using all 4 slots. But who knows.
FYI, I have the 8-core version of this iMac.
Also bought in Dec 2020.
Also bought 128GB of RAM from OWC.
Got kernel panics frequently.
Realized it happened less if all slots weren't full.
Also went through the process of replacing for all four sticks through OWC's replacement policy.
With replaced RAM, crashes happen less frequently, but still happen. Which is why I'm back to searching the internet for similar stories in search of a solution.
Very frustrating.

Edit: two full kernel panics in the last 30 minutes. I will try pulling out one stick.
You might try replacing them all again with OWC. If you go through 3 replacements and the issue persists you could get a refund (under lemon law) and try another brand like Crucial. I feel for you, this kind of absurdity is exactly what you hope to avoid when buying a new Mac.
 
Thanks, Jeremy. Keep us posted how your system performs as time goes by. You don't have any OWC in your system anymore?

I temporarily thought the replacement cured my issues. I don't know if what's cropping up is something like a heat issue with this particular RAM when all four slots are full (just a wild guess) or some other reason. But it seems more stable when it's just three slots full at random, with three sticks picked also at random. But when all four are together, that's when the trouble starts.

I might just try to sell one of the sticks of 32GB as they all seem to work fine on their own. To UPS the sticks back to OWC from Canada with insurance, I think it cost me like $50 US. But if it takes three replacements to get your money back, I might keep that an option.

I wanted a 128GB system to eliminate the complexity of a VEPro network, but I think 96GB is where I'll have to stay.
I'm still using OWC. I tried a different brand (Timetec) but it didn't work out. OWC paid for shipping the second time I had to replace with them. I'll post any updates as they happen.
 
Just a thought....but maybe try just putting the Apple Ram back in (you probably just have 8GB) and see if it happens. If it doesn't, then you know it's a Ram issue. If it does crash, then you have some ammo for taking the iMac back to Apple for a replacement.
 
I also have an OWC RAM kit for my Early 2008 MacPro (which I'm still using :P). One pair of the RAM sticks caused an issue with a blank screen on startup and flashing power light. I removed the RAM pairs one by one to find the offending set, and ever since I took it out the computer has been OK. I even got a replacement for those faulty RAM sticks from OWC under warranty, but after a few weeks the computer started showing errors again until I took the new sticks out. I basically just left them out from that time on, as I'm not sure if it's the OWC RAM causing the issue or those specific RAM slots or something else. Basically I've just been living with a bit less RAM in this machine rather than fight it.
I was literally recalling the exact scenario on my 2008 Mac Pro. I methodically paired various combinations of sticks (including with the Apple Ram to have enough to test with) to pinpoint the faulty hardware. Ended up using less for years until a new Mac in 2015. I’m on a 2019 iMac now, and still using OWC (64 gb) so clearly I got a bit of confidence back.
 
I'm still using OWC. I tried a different brand (Timetec) but it didn't work out. OWC paid for shipping the second time I had to replace with them. I'll post any updates as they happen.
I’m curious if there is a potential pattern emerging, as it seems others are reporting issues with select configurations of the 2020 iMac and OWC sticks. Did anyone else get this impression? A faulty manufacturing run is not entirely out of the question.

I’ve had all kinds of weirdness from things ordered, replaced and defective this past lockdown year. I’ve made less sense as a person as well, lol.

Given you haven’t reported issues in a few weeks, please do let us know if you think the saga is over. These kinds of discussions definitely can help point to potential patterns, and benefit others with similar setups.
 
It's been about 3 weeks since I installed the 3rd round of modules from OWC and I haven't had any panics during that stretch. I don't want to jinx it, but it seems to be resolved.

From what others have reported there does seem to be a pattern with iMacs and RAM expansion, particularly with OWC memory. But it's hard to say if RAM manufacturers or Apple are to blame. Of course Apple won't take any responsibility for 3rd party RAM. This whole saga in addition to a recent fiasco with Time Machine really put me off from buying another Mac.
 
It's been about 3 weeks since I installed the 3rd round of modules from OWC and I haven't had any panics during that stretch. I don't want to jinx it, but it seems to be resolved.

From what others have reported there does seem to be a pattern with iMacs and RAM expansion, particularly with OWC memory. But it's hard to say if RAM manufacturers or Apple are to blame. Of course Apple won't take any responsibility for 3rd party RAM. This whole saga in addition to a recent fiasco with Time Machine really put me off from buying another Mac.
I'm glad you seem to have gotten the RAM problem sorted.

I hear you on Time Machine. I can't go more than a year or two without having to do a complete volume rebuild (the Time Machine backup becomes corrupted). I don't really trust Time Machine these days, so I use Carbon Copy Cloner, which is as fantastic as Time Machine is frustrating.
 
I'm glad you seem to have gotten the RAM problem sorted.

I hear you on Time Machine. I can't go more than a year or two without having to do a complete volume rebuild (the Time Machine backup becomes corrupted). I don't really trust Time Machine these days, so I use Carbon Copy Cloner, which is as fantastic as Time Machine is frustrating.
+1000 to this - I've relied on Carbon Copy Cloner for years, and it's been fantastic. It scales from very basic (back up this one drive to this other drive) to very complex (back up this drive when I connect this backup drive, then back up this volume to this folder (but ignore these subfolders), then back up this third volume, and also remind me when I haven't run the backup job in over two weeks).

I haven't used Time Machine in several years, mainly because my existing backups work so well. The current version of Carbon Copy Cloner can work very much like Time Machine (with versioning, etc) if you need that, as well.
 
Ram is crucial for Mac's, they use Kingston but charge way to much for memory expansions.
So buy the same type of Kingston memory and run without any trouble.
At least that is what I've done with all my Mac's (iMac, Mini,...) and also do for the iMacs
of my customers. Haven't had a RAM issue in decades. (Really, no joking or bragging).
But this applies to Windows machines also : Kingston is a proven quality label for RAM,
and I'm glad I always use or advise to use this brand. Keeps me and my clients happy...
 
Ram is crucial for Mac's, they use Kingston but charge way to much for memory expansions.
So buy the same type of Kingston memory and run without any trouble.
At least that is what I've done with all my Mac's (iMac, Mini,...) and also do for the iMacs
of my customers. Haven't had a RAM issue in decades. (Really, no joking or bragging).
But this applies to Windows machines also : Kingston is a proven quality label for RAM,
and I'm glad I always use or advise to use this brand. Keeps me and my clients happy...
Kingston sells good RAM, but Apple does not source their memory from Kingston.
 
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