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DDR5 ECC UDIMMs with CROSSHAIR X670E EXTREME and Ryzen 9 7950X?

Level 8
The official specs says that CROSSHAIR X670E EXTREME supports ECC memory and so does Ryzen 9 7950X. It took a while to find a vendor with DDR5 ECC UDIMMs in stock, but I finally got the Kingston Server Premier DDR5 4800MT/s ECC UDIMMs last week and the system I put together last night doesn’t work.

Relevant parts of the build:

[TH="class: _3TNkDptlyGOiWXvdX_acOB"]Component[/TH]
[TH="class: _3TNkDptlyGOiWXvdX_acOB"]Product[/TH]

ProcessorAMD Ryzen 9 7950X
RAMKingston Server Premier DDR5 4800MT/s ECC UDIMM
Power supplyCORSAIR AX1600i Digital ATX Power Supply

With peripherals connected, I observed the following:

  • No display output, although the USB-C-to-HDMI dongle LED is on.
  • USB optical mouse laser is off (no power).
  • USB keyboard LEDs are off (no power).
  • Front panel USB-C port can charge my phone.

Q-Codes observed during startup with the DIMMs in slots A2, B2, A2 + B2, or all the slots:

[TH="class: _3TNkDptlyGOiWXvdX_acOB"]Q-Code[/TH]
[TH="class: _3TNkDptlyGOiWXvdX_acOB"]Meaning[/TH]
[TH="class: _3TNkDptlyGOiWXvdX_acOB"]Duration[/TH]

00Not usedSplit second
C1(unknown; not in MB documentation’s Q-Code table)Split second
46(unknown; not in MB documentation’s Q-Code table)Split second
91Driver connecting is startedSplit second
00Not usedSplit second
15Pre-memory System Agent initialization is started60 seconds
00Not usedSplit second
CC(unknown; not in MB documentation’s Q-Code table)Split second
00Not usedSplit second
00Not usedSplit second
99Super IO initializationFinal state (forever)

I checked ASUS’ general troubleshooting page (Intel-specific rows removed):

[TH="class: _3TNkDptlyGOiWXvdX_acOB"]AMD Motherboard Q-Codes[/TH]
[TH="class: _3TNkDptlyGOiWXvdX_acOB"]CPU abnormal[/TH]
[TH="class: _3TNkDptlyGOiWXvdX_acOB"]Memory abnormal[/TH]
[TH="class: _3TNkDptlyGOiWXvdX_acOB"]Graphic Card abnormal[/TH]
[TH="class: _3TNkDptlyGOiWXvdX_acOB"]Others abnormal[/TH]

B0, 99, 15, 53✔️✔️
00, 19, 30, 40, 55✔️✔️✔️
A0, A2Boot up device abnormal
B2External device abnormal
A9Boot into the BIOS
AABoot into the system

It seems like I should focus on either CPU or memory.

I’ve already attempted these troubleshooting steps:

[TH="class: _3TNkDptlyGOiWXvdX_acOB"]Component[/TH]
[TH="class: _3TNkDptlyGOiWXvdX_acOB"]Action[/TH]
[TH="class: _3TNkDptlyGOiWXvdX_acOB"]Result[/TH]

PSUConnect all the connectors.Already double-checked that they were all connected.
CPUCheck for dirtThis what what I did before putting the CPU in.
CPUCheck for broken pins (not applicable to AM5 CPUs now, but applicable to the MD socket)I took the fan and heatsink off and removed the CPU to inspect the pins in motherboard CPU socket. They look fine to me.
RAMCheck for dirtAlready vacuumed the motherboard and inspected the RAM modules themselves.
RAMTry the different configurations.Slots A2 and B2 alone or together and all four slots exhibit the behavior I described. Using either slots A1 or B1, though, result in a Q-Code C5, which is not documented, but they also non-recommended memory configurations. And just for completeness, no RAM modules installed results in a near-instantaneous Q-Code of 10 (PEI Core is started).
PeripheralsRemove all peripherals.Already tried with and without.
Clear the CMOS.No changes to symptoms.
Switch BIOS (on dual-BIOS boards).No changes to symptoms.

From Googling Q-Code 99-related issues, one commenter noted that it’s probably storage-related. But installing the PCIe 5.0 M.2 adapter (which comes with the motherboard) with a stick of memory didn’t change the outcome.

I plan to substitute the RAM kit next. I already have a RAM kit on the motherboard’s QVL in my shopping cart (CORSAIR CMT32GX5M2B6000Z30K) which can ship in a few days and would still be within my RMA period. If that doesn’t work, I’m not sure what to do.

If RAM incompatibility is the real problem, is there any expectation of RAM support being expanded with new BIOS updates? There is a post about a similar issue on a different forum and about different motherboard manufacturer, but it mentions that:
I had to update the BIOS from 1.03 to 1.09 for it to POST with the new RAM.

Edit: added BIOS note

Level 8
Now I am able to get the board to start and the USB4 port to output something. I can see the hardware properties in the UEFI BIOS. The fix was not obvious to me but I had to flash the board with the latest BIOS update. Thanks to a kind stranger for suggesting it.

This was not a PSU, CPU, nor RAM problem, but a MB BIOS problem.