Please post more details about your setup.
What make and model RAM? Are all the modules matched or did you buy some later? Check the labels on each stick - are they all the same version numbers? Different version numbers indicate different DIMM manufacturers and different controllers (e.g. Samsung or Hynix), which can sometimes produce instability.
What are you running the RAM on, XMP profiles? Any adjustment of RAM voltage? What version firmware BIOS? What is your OC configuration? The more info you post, the more likely you are to get replies... 🙂
While I don't have first-hand experience of this problem on Ryzen (are you running TR2 or TR3?) myself and a few friends have put together some useful reading.
Welcome to the wonderful world of timings and voltages. Is your RAM the Corsair Vengeance LPX Black 256GB 3200MHz 8x32GB kit? (CMK256GX4M8E3200C16)
Those modules' advertised timings are CAS 16-20-20-38 at 1.35V, on X399 you'll probably need to tweak. Either run a higher CL to achieve 3200 MHz, or run slower frequencies with tighter CL.
AIUI with Ryzen it's in your interest to keep frequency as high as possible and run higher CAS latency because CCX bandwidth is tied to memory speed.
The ROG Zenith Extreme Alpha was advertised as supporting 8x DDR4-3600 up to 128 GB max, so you're pushing the envelope quite a bit. I know a few people have got 256 GB working but with quite increased CL timings - e.g. https://benchlife.info/rog-zenith-extreme-support-32gb-non-ecc-ddr4-reach-256gb-01212019/ , CL20 (CL20-19-19- 43)
I've read that Vengeance LPX RAM can be problematic for a couple of reasons; some people suggest the older LPX is better optimised for Intel, although the Vengeance RGB variant apparently works better with AMD. Take that with a pinch of salt. Others seem to run ADATA, Hynix or Samsung fairly happily. Is your RAM on the QVL for the board? Any reason for not buying Crucial/G.Skill/Geil etc?
Running 8x32 sticks is definitely going to tax the IMC :). You might be unlucky with the RAM and motherboard combo so you'll need to compensate on the memory timings. Get the freeware version of Thaiphoon Burner and read the module info to see whether your RAM is B-Die / E-Die. If you've not lucked out with B-Die you may not be able to push it quite as hard.
Have you tried slightly increasing the SOC voltage? And what CL, T (1T/2T) and voltages is the XMP/DOCP profile setting?
I'd try adjusting the SOC voltage very slightly (1.10 or 1.15 V max) and bump the RAM voltage slightly to 1.35 or 1.4 V and start with a slower frequency (2666, 2800, 2933), then try looser timings and dial in from there.
The Ryzen DRAM Calculator app will probably save you lots of time. Also check whether RAM Power Down Mode is disabled in the BIOS.
This topic really interested me as I'm planning my own Ryzen build. From discussions with a few friends (with considerably more Ryzen experience) and my own research, I've put together some links below for reference. Some useful stuff covering TR 2 and 3 series RAM stability and a handy reddit post with jargon demystifiers.
- https://www.techpowerup.com/download/ryzen-timing-checker/ (retired but still occasionally useful)
- https://adoredtv.com/community/postid/1456/ (and full thread, https://adoredtv.com/community/hardware-forum-hardware-forum/getting-ram-stable-on-picky-ryzen-syste...)
Very interested to hear how you get on. Also welcome other people's thoughts if I've suggested anything odd, I've been i7 and i9 for a while now so I'm reeducating myself as well!