new beta bios for X399 is up on ASRock site

Ok, running the 3.33A too now. For now they removed the additional performance boost options from the first TR Gen. 

I've got low grade B-Die Samsung which only achieves CL16 instead of 14 @ 3200MHz and I've never had much problem with stability as long as I used DRAM Calculator. No difference in stability for me between all previous STABLE BIOS versions. I have not tested the previous beta that people reported as buggy, but I am on 3.33A now.

Hi and welcome.
RyZEN Dram Calculator is the main tool to reach stability on ZEN* platform.
Plus in the thread I'll link you will find also a custom profile for TM5 (to test for stability of RAM.
https://www.overclock.net/forum/13-amd-general/1640919-dram-calculator-ryzena-1-4-0-1-overclocking-dram-am4.html

Basically now nearly every set of modules provides good results, but I personally would look for the Samsung B-Die modules.

FabienC44 wrote: Thanks SoniC ! Reading your last sentence, I hope that my MB isn't defective :/

Don't give up - my "golden" memory also would not want to run with the "stock XMP" setting and required fine-tunning with the help of RyZEN DRAM Calculator but I finally reached the 3200 CL14 stable with nicely tuned timings :)

Seems that HX430C15PB3K4 is Hynix M-die (according to the ASRock memory compatibility charts) and with two pieces it should run 3000 stable.
I assume that with the newest UEFI/BIOS it also should run 4x 8GB stable.

RyZEN DRAM Calc to the rescue! Run it, press "R-XMP",
Start with Threadripper 1gen, then select either Hynix MFR OR some sites name this kit as Hynix CJR -- you need to test by yourself using the Thaiphoon burner which kit is this exactly (or d/l latest AIDA64 to check).
Then Profile V1, Memory rank 1 (as these are single rank at least according to my knowledge), then frequency 3000 and dimm modules '2'.

Then press calculate safe.
Do a few shots with your mobile- do shots from main, advanced and power supply pages.
Then go to your UEFI, load default values, save and reboot into UEFI again. Upgrade UEFI to the newest (I use the 3.33 beta and it is fine on my X399 FPG), let it reboot with safe timings, and boot to UEFI again. If you are on a <2.10 release then do not forget to use the Bridge BIOS before going to 3.x.

Back in UEFI start with most conservative values (at first we need to make sure that the speed is holding, then we can tune it up)
with that I mean -- e.g.:
use tRFC (alt) values (&round it up) -> 356.6=357
Everything else set to Recommended values except :
Gear down to disabled, Command Rate 2T
Apply them and let it reboot.
If it is in a boot loop then reset CMOS and boot into UEFI again.

Before trying alternative values set everything as it was before the clear CMOS EXCEPT Memory clear - leave it enabled.

I don't know why but the calc recommends disabling it at first but my system is in a boot loop when set to disabled.
So try this before cycling through alternative values.
If you have more problems you can post in the RyZEN DRAM Calc thread... there are a lot experts and gurus with knowledge far beyond my imagination.
But before doing that - read read and read once again,
you will get your rig stable eventually (and learn a whole lot about the memory (sub)timings additionally

i am looking at the QVL list of X399 Taichi

i plan to get a Threadripper 2950x

Can someone explain to me how to read the DIMM Socket Support?

I am looking at this particular model
CMW32GX4M4D3000C16

if its 2, does it mean it has only been tested with 2 sticks? or it's guranteed to work with 2 sticks only.

meaning can i buy a 4x8 kit, is it at my own risk?