Problem with RAM upgrade on Precision 3660 Tower

I have the same problem, I tried a few different manufacturers and none works. I spoke to Dell.com and they told me I must use their original memory cards. I bought two 16gb from them and it turned out that they do not work in dual channel ... you can use them only in slots 1 and 3 or 2 and 4 but they work in single channel. I spoke to dell again and no one has an answer to my questions ... that's stupid

The systems use to be a bit picky about the ram, but this is the first time I see troubles with Crucial. It's one of the usually recommended alternatives

Dang, this is a big issue then, that Dell needs to fix ASAP. So you have tried Kingston? Like the one I referenced in the above post? and it did not work?

Kingston PN: KCP548UD8-32

Chalk up another one.  I just tried to install a Crucial 2x32 GB DDR5 kit (CT2K32G48C40U5) and got the 2/5 amber/white light code.  I checked the Crucial website before purchasing two days ago and this was the kit recommended.  In my case, it's two sticks of RAM and I have a hard time believing two sticks of Crucial RAM are defective out of the same package.  I've used Crucial for years and never had a problem until now.  Time to have a conversation with Dell.

+1 unhappy user.  Just bought a brand new Precision 7920.  Replaced factory RAM with 24 x 32GB Kingston modules.  No POST.  Machine would only boot with 8 of the 24 sticks installed (oddly, in the wrong slots, so that I was stuck with a 2DPC config).  

RMA'd all modules back to Kingston: luck was no better with the replacement sticks.  Then I switched to Samsung for my 3rd attempt: the machine still won't take more than 256 GB.  No final decision yet but very frustrated.

Benchmarks I performed on the two bootable configs (256 GB from Kingston, then 256 GB from Samsung) came in at about 40% of expected performance.

During endless Googling, read that some bad boards or CPUs will "drop" a channel when they malfunction.  That's my current theory but who knows.

@blakeu , did you try also all these combinations ?

All the 32GB ones, yes.  No dice.  After talking to Dell support, though, they offered to send a field person with a replacement motherboard.  Perhaps there was no RAM/system incompatibility after all?  I might post again if/when the system is working.

Well, that would be a way better outcome, if it's due to a mb defect. The majority of us don't add ram that quickly or at all, so if there's a defect it would lie dormant

My vendor replaced the 32GB crucial kit with another 32GB kit from crucial. As expected this kit also doesn't work. Its very disapointing. I'll try to contact crucial and/or Dell. Maybe a solution can be found but I think the one says it's a problem of the other one.

now I had a call with Dell. As expected they say that the ram is not compatible. Only ram with 4400mhz is supported... so there is no help from Dell side.

I also had a support chat with crucial. They are sure that the ram is compatible (I gave them the specs of the original Dell ram: SK Hynix HMCG66MEBUA081N). After trying some troubleshooting we found no solution. Now this issue is forwarded to their internal team and then I should get a feedback.

Unfortunately, I gave up and after many unhelpful conversations with Dell, I decided to buy two memory cards from them that finally work. It seems that dell wants to be like an apple and make us use only parts from them...

Just following up on my earlier comments.  Dell has finished performing the 7920 motherboard replacement on site & I am having much better luck with the new unit.  All 24 32GB DIMMs are now POSTing OK and recognized by Windows, for a total of 768 GB (actually 766.66 GB after hardware 'reservations').  Here is the memory kit I used, for those interested:

• Samsung M393A4K40BB1-CRC 24x32GB

There was a lot of doubt right up to the end, since the Precision 7920 manual makes no reference to 2400 MHz RAM (only 2666 MHz and higher).  But if the two Xeon Silver CPUs installed are going to clock the memory down to 2400 MHz, anyway, the 2400 MHz sticks made sense to me.  With the new board, they are working.

Now that we know the motherboard was at fault, there was probably no compatibility issue with the 3200 MHz Kingston RAM that I started out with.  My take-away is that, despite suspicions I was starting to have about Dell, they have to buy memory from the same places we do (Samsung in this case).  Their PCs should be upgradeable like anyone else's.  Don't believe otherwise.

Of course, they sold me a faulty board originally, alas, but obviously they've stood by the warranty as well as the on-site support agreement (which, by the way, I got for free as part of a promotion).  Good luck, upgraders!

I guess this is not true. I bought the official 32GB DDR5 module from Dell and those are 4800MHz! And they work.

BTW. The same problem as you, bought the 3660 with 16GB (2*8) and ordered the Crucial 2*32GB Kit as mentioned on the compatibility site and got the 2/5 amber/withe flashing. Kingston Ram (2*32GB) is not working as well.

My conclusion: Dell 3660 does only support the original Dell Memory module  

I know that it's not true. Also the installed 2*8 GB modules are 4800MHz modules. The support simply had no clue of it.