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Journeyman III

5800x3D not POSTing if any RAM stick is installed in slots 3 or 4


RTX 3080
2x16 GB Trident Z Neo DDR4 RAM (3600 MHz, 18-22-22-42)

I was upgrading from a 3700x to a 5800x3D. I updated the BIOS to the latest, version 1J with a release date of May 2023, which is newer than the version which explicitly calls out support for the 5800x3D. The computer does not POST if there is any RAM present in slots 3 or 4. Specifically, the mobo has slots A1, A2, B1, B2. If I have either stick of RAM in channel B, it doesn't post and all I get is a solid red CPU light on the mobo. When I drop the 3700x back in, it boots just fine with both sticks. With the 5800x3D, I can boot with either stick of RAM in either of slots A1 and A2.

Things I've tried:

I bought a second 5800x3D from amazon, I currently have both in my possession. Both CPU's exhibit identical behavior - does not boot with any RAM in channel B
I swapped out for a different pair of RAM. Same problem, does not boot with any RAM in channel B
Shorted CMOS jumper on mobo to reset BIOS to default, no change in behavior
From default BIOS state, booted with one stick of RAM, explicitly set RAM speed to 3200 MHz, and inserted second stick. No boot.
Cleaned the CPU socket with isopropyl alcohol and sprayed down with compressed air. Reseated both 5800x3Ds multiple times, no boot.

My thoughts:

Because it boots just fine with 3700x, I know the slots on the mobo are fine.
It seems unlikely to me that both 5800x3D are both defective in the same way. Did my mobo somehow fry the second memory channel?
I initiated a return with Amazon on the first CPU and I don't feel great doing an RMA on 2 CPU, but I didn't pay $300 to kill my dual channel RAM. If I need to buy a new motherboard, I would rather just upgrade to AM5 and get a different CPU. 

What do?

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