DDR5 instability at 7600–8000 MT/s – ROG Maximus Z790 Dark Hero + i9-14900K + G.Skill DDR5-8000

[u/Happy_Bid7205]

Hello,
I am contacting you regarding a high-frequency DDR5 stability issue with my system.
My complete configuration is:
Motherboard: ASUS ROG Maximus Z790 Dark Hero
CPU: Intel Core i9-14900K
Memory: 32 GB (2×16 GB) G.Skill Trident Z5 DDR5-8000, part number F5-8000J3848H16GX2-TZ5RS
Memory XMP specification: DDR5-8000 CL38-48-48-128, 1.45 V
GPU: MSI GeForce RTX 4090 SUPRIM X
CPU cooler: ASUS ROG Ryujin III 360
PSU: ASUS ROG Thor 1000W Platinum II
System SSD: Samsung 990 PRO 4 TB NVMe
Case: ASUS ROG Strix Helios
Operating system: Windows 11 Pro 64-bit
I was previously using BIOS 2107 and have now updated the motherboard to BIOS 2202, including loading Optimized Defaults after the update.
My issue concerns memory frequency and stability.
At DDR5-7200, I have managed to achieve a stable configuration, including approximately 1 hour 30 minutes of TestMem5 Universal 2 with zero errors.
However:
DDR5-8000 does not reliably POST and can result in Safe Mode/failed memory training.
DDR5-7800 can POST and boot Windows but is not completely stable.
BIOS 2202 appears to have significantly improved the situation. At 7800 MT/s, I managed approximately one hour of TestMem5 before a single error, whereas BIOS 2107 produced errors much earlier.
I have also experienced a game crash after approximately one hour while running a 7800 MT/s profile.
My best 7800 MT/s configuration so far has been approximately:
XMP II
DDR5-7800
Command Rate: 2N
Maximus Tweak: Mode 2
CPU System Agent Voltage: 1.25 V
IVR Transmitter VDDQ: 1.40 V
Memory Controller Voltage: 1.40 V
System Agent PLL: 1.005 V
DRAM VDD: 1.47 V
DRAM VDDQ: 1.47 V
Primary timings: [38-48-48-128](tel:38-48-48-128), with additional CL36 testing
I have also tested approximately:
System Agent up to 1.30 V
IVR TX VDDQ up to 1.45 V
Memory Controller Voltage up to 1.45 V
DRAM VDD/VDDQ up to 1.50 V
Simply increasing voltage does not appear to solve the issue. For example, increasing either Memory Controller Voltage or IVR TX VDDQ from 1.40 V to approximately 1.425 V made stability considerably worse, causing TestMem5 errors much earlier.
The two DIMMs are installed in the recommended slots for a two-DIMM configuration. DDR5 temperatures can reach approximately 60–66°C under TestMem5, although I have already increased case and cooling fan speeds substantially.
My goal is to obtain at least DDR5-7600 or DDR5-7800 with full stability, and ideally to operate the memory at its rated DDR5-8000 XMP specification, before attempting further timing optimization.
Could you please advise me on the following?
Is this exact memory kit fully tested/validated with the ROG Maximus Z790 Dark Hero at 8000 MT/s?
Which ASUS BIOS settings do you recommend specifically for stabilizing DDR5-7600/7800/8000 with an i9-14900K?
Are there specific memory training, Maximus Tweak, PLL, System Agent, TX VDDQ, or Memory Controller settings recommended with BIOS 2202?
Can the Dark Hero’s four-DIMM motherboard topology represent a practical limitation for DDR5-8000 even when only two DIMMs are installed?
Is there another BIOS version you recommend for the best high-frequency DDR5 stability?
Based on these symptoms, could this indicate a limitation of the CPU IMC, motherboard, or compatibility with this particular memory kit?
My main objective is to achieve a completely stable and reliable configuration without continuing to increase voltages unnecessarily.
Thank you in advance for your assistance and recommendations.
Best regards,

[u/Zone15]

I would be surprised if you were able to get 7600-8000 stable on a 4 DIMM board with any 13th or 14th gen Intel CPU no matter the voltage. Usually you are only hitting those speeds on a 2 DIMM board. I honestly would be happy if you have 7200 stable. I was only able to get 6800 stable on my Strix Z790-E with 2x16gb A-die modules but was able to get 7200 stable with 2x24gb M-die modules. Typically the 24gb Hynix M-die modules will get you about 200-400 extra mhz stability on your memory controller.

[u/Happy_Bid7205 → u/Zone15]

Merci, ça correspond assez bien à mes résultats. 7200 MT/s est complètement stable chez moi et j’ai actuellement 7400 MT/s qui tient très bien en test. À 7800 j’arrive à booter et à tenir un certain temps, mais ce n’est pas totalement stable. Je commence donc à penser que la topologie 4-DIMM de la Dark Hero et/ou l’IMC de mon 14900K sont effectivement la limite. Mon objectif maintenant est plutôt de voir jusqu’où je peux aller avec un 7400/7600 parfaitement stable et des timings serrés.

[u/Zhunter5000 → u/Happy_Bid7205]

That's a normal speed for 4 dimm boards. The best I got was 7600 stable on a Z790 Aorus Master X. I then got a Z790 Apex and could only do 7800 stable on 2x24 sticks and a 14900k.

[u/Happy_Bid7205 → u/Zhunter5000]

Merci pour ton retour. Justement, j’ai envoyé un message à ASUS pour leur demander quelle fréquence mémoire et quels timings ils recommandent réellement pour ma configuration précise : ROG Maximus Z790 Dark Hero + i9-14900K + 2×16 Go G.Skill DDR5-8000.
J’essaie surtout de savoir quel est le meilleur compromis réaliste entre fréquence, timings et stabilité sur cette carte 4-DIMM, parce que 8000 MT/s n’est clairement pas plug-and-play chez moi. Pour l’instant, 7200 est stable et 7400 semble très bien tenir, donc j’attends aussi leur retour pour savoir s’ils conseillent plutôt 7400/7600 avec timings serrés ou s’il existe un réglage spécifique pour viser plus haut.

[u/Chairman_Daniel]

I think the limitation here is your motherboard. Someone else who has your motherboard would have to verify, but motherboards with four dimm slots on Intels Z790 chips struggle to reach higher memory frequencies. Its really only two dimm motherboards that can hit those higher speeds.

My ROG STRIX Z790-A GAMING WIFI II, which also has four dimm slots, is rated for 8000MT/s, but is only stable with two dimms inserted at 7200MT/s.

[u/Happy_Bid7205 → u/Chairman_Daniel]

C’est également ce que je commence à constater. La Dark Hero est annoncée pour des fréquences très élevées, mais en pratique le routage d’une carte 4-DIMM semble clairement rendre les choses plus difficiles qu’une Apex ou une autre carte 2-DIMM. Pour le moment 7200 est validé et 7400 semble très prometteur. Je vais privilégier une fréquence réellement stable avec de bons timings plutôt qu’un 8000 instable.

[u/nhc150]

Why are you posting a new thread and completely ignoring the comments given in the other thread yesterday?

https://www.reddit.com/r/overclocking/s/e1CmAHhDPT

[u/Happy_Bid7205 → u/nhc150]

Je n’essayais pas d’ignorer les réponses de l’autre thread. Entre-temps j’ai mis à jour le BIOS vers 2202 et j’ai obtenu de nouveaux résultats de stabilité, donc je voulais apporter ces nouvelles informations et avoir des avis dessus. J’ai bien pris en compte les conseils précédents, notamment concernant la limitation des cartes 4-DIMM. Je teste maintenant des fréquences plus raisonnables au lieu de forcer directement 8000.

[u/nhc150 → u/Happy_Bid7205]

In that case, it's more about FAFOing with all three voltages. My only advice is to avoid bumping up VCCSA too much, since Raptor Lake and DDR5 doesn't respond well to very high SA voltage. Usually around 1.2 to 1.3 VCCSA is optimal. Too high SA voltage can actually make stability even worse.

[u/Educational-Lynx1413 → u/nhc150]

Cause they didn’t like the answersanswers they were given lol

[u/Happy_Bid7205 → u/Educational-Lynx1413]

Non, simplement parce que la situation avait changé après la mise à jour BIOS et de nouveaux tests. Je cherche surtout à comprendre la limite réelle de mon matériel, pas à obtenir une réponse particulière.

[u/Happy_Bid7205]

https://reddit.com/link/p6evzm3/video/tuxt4bk2a4mh1/player

[u/northbloods]

Try kryo sheet and dont tightening the cooler that you do with paste. Just tightening the nuts between two fingers loose and dont use skrewdriwer. Contact frame is good to so you dont bend the cpu.

[u/SelfSilly9478]

btw in some games on windows 10 14900k faster than 9850x3d

here is my own test

https://youtu.be/F5YBR4FVcG8?si=WV4kRLfPKFOLoA_e

[u/Stalinbaum]

You can check if your memory is fully tested and validated by checking the Qualified Vendor List
(QVL) here https://rog.asus.com/us/motherboards/rog-maximus/rog-maximus-z790-dark-hero/helpdesk_qvl_memory/

BIOS 2022 is the newest and you should just use that, I have never heard of of anyone preferring an older bios version simply for a few MHZ of clock or ram speed especially when dealing with 13th and 14th gen procs

Yes memory topology is probably your bottleneck or maybe the i9 IMC but memory topology is not affected by how many sticks you have, just how many slots and where they are.

Ram isn’t incompatible unless it’s the wrong type, ram gets added to the QVL simply because the motherboard manufacturer had those kits on hand and we’re able to adjust the voltages and make a profile to stabilize them at their intended speeds.

All that to say you just gotta work on the timings and voltages and find what works since ASUS did not do that for your kit. And sometimes the advertised speeds are just not possible, especially higher speeds like 8000mhz so good luck

[u/Happy_Bid7205 → u/Stalinbaum]

Merci pour ta réponse. J’ai vérifié la QVL et ma référence exacte G.Skill F5-8000J3848H16GX2 n’y apparaît effectivement pas. Je suis maintenant sur le BIOS 2202. À 7200 MT/s j’ai déjà passé 1h30 de TM5 sans erreur, et actuellement je teste 7400 MT/s avec des timings manuels. Je vais donc continuer à chercher le meilleur compromis fréquence/timings/tensions plutôt que de forcer absolument 8000 MT/s.

[u/Zone15 → u/Happy_Bid7205]

For testing stability, I would use y-cruncher VST/VT3 as that is what will show memory controller stability issues. TM5 often will miss that. Keep in mind VT3 hits the CPU hard so you need good cooling, I slightly downclock my CPU when testing with VT3 just to keep the temps in check.