Z790 Taichi XMP unstable @6800mhz

Hi all,

Specs:
i7-13700K (stock NO OC)
Asrock Z790 Taichi
MSI RTX 4090 Gaming X Trio
Samsung 980 Pro 1TB
Corsair HX1500i (2022 model)
G-Skill F5-6800J3445G16GX2-TZ5RK

I had a couple of game crashes so i checked data log within Windows 10 and i suspected RAM issue.

I run full Memtest86 with XMP profile and within 10 sec had 3 errors.
Then i loaded "optimal defaults" in BIOS to run RAM frequency at INTEL default, run full Memtest86 again NO errors = PASS.

Then i loaded XMP again this time i lowered RAM frequency from 6800 to 6000mhz, run full Memtest86 again NO errors = PASS.

The RAM i have is on Asrock QVL list ---- G-Skill F5-6800J3445G16GX2-TZ5RK

So what is causing this board not to run my RAM stable at the advertised speed of 6800mhz? Yes i can play games but they did crash i can surf internet i tested GPU with 3Dmark no issues tested CPU with Cinebench zero issues with XMP and optimized default. Do i need to change certain settings in BIOS other then simple enable XMP?

Thanks in advance

RLGL wrote: XMP is an overclock. There is no guarantee it will work. You may have to relax the timings a bit or settle for a lower speed.

That's true however 6800mhz isn't that high of an overclock i mean i understand if your using 7200mhz + kits thats a different story.

Regardless its weird when i set XMP but at 6600mhz it also fails Memtest86 albeit after 1.5 hours, XMP 6800mhz fails under 1 minute.

Upon further research as others had similar issues you can buy a 7200mhz kit on the boards QVL list and do -----> minus 400mhz and magically it passes Memtest86. So i did the same from 6800 to 6400mhz and it passed. It seems manufacturers LIE about the speeds just so they can brag! Made a thread on another site:

https://www.overclock.net/threads/help-with-6800mhz-xmp-on-z790-mb-solved.1805765/

And only Gigabyte seems to acknowledge the minus 400mhz to make it work!
Common clearly something wrong with the BIOS because if it was a faulty KIT i would have errors even at default. Anyway ive loaded optimal defaults THEN enable XMP but at 6400mhz tested it with FULL Memtest86=PASS, Prime95 (torture test for memory controller and ram option) 1 hour = PASS, OCCT memory test 1 hour = PASS after that i changed the CAS timings from CL34-45-45-108 -> CL30-39-39-(39)-79. Done again all the tests all is passed. No tweaking the voltage it was set to 1.40v ram volt.

If people have similar issues as mine TRY to enable XMP BUT lower RAM frequency by 400mhz regardless of the kit could be 6000mhz becomes 5600mhz, 7200 becomes 6800mhz etc etc.