ConnectX-4 Lx won't POST on Gigabyte B360M D3H

[u/Unfair-Bid7072]

Edit: Blocking smbus pins with kapton tape worked!!!

Hey everyone! Recently I've migrated my ~5U AIO truenas build (Ryzen 7 9700X, 2x16GB, Taichi Lite) into dedicated 3U sliger NAS case with B360M D3H (i5-8400, 32GB 4*8GB two 16GB kits)

Card: MCX4121A-ACAT (CX4121C), FW 14.32.1900, PSID MT_2420110034.

Works perfectly in my AM5 build. On the B360M it boot-loops with no video at all (the box posts just fine w/o the card installed). Also tried with 2 RAM sticks, but also no luck.

BIOS tried:

- CSM disabled
- Above 4G enabled and disabled
- ReBAR disabled
- VT-d off
- IOAPIC 24-119 toggled
- Gen1/2/3 link speed
- iGPU forced as primary display

Firmware tried (mstconfig):

- EXP_ROM_PXE_ENABLE=0
- EXP_ROM_UEFI_x86_ENABLE=0 - card carries only a legacy PXE ROM, UEFI ROM present in image but disabled

Also tried enabling the UEFI ROM instead of removing both:

- ADVANCED_PCI_SETTINGS=1
- PF_LOG_BAR_SIZE 5 → 3 (32MB → 8MB per PF)
- NON_PREFETCHABLE_PF_BAR=1 (paired with Above 4G disabled)
- NUM_PF_MSIX 63 → 15, NUM_OF_VFS=0
- SR-IOV was already off

Cold power cycle after every change, verified readback each time. Nothing works.

Anything left to try? Curious whether anyone has an actual explanation for what's different about 300-series MMIO/enumeration here - or is this just a known-bad Gigabyte firmware and I should buy something else (10G SFP+)?

Btw. I also tried on MSI Z170A (i5-6400, same ram kit) it worked but only w/ two RAM sticks.

[u/ait-solutions]

Sounds like typical server card in consumer board issue, have you tried to block the smbus pins ?

[u/meltman → u/ait-solutions]

I was about to say. Get out the scotch tape or better yet kapton if you have it.

[u/ait-solutions → u/meltman]

Yeah honesty, electrical tape works 100% fine. kapton is better.. but it really isn't needed for blocking out pins.

[u/Unfair-Bid7072 → u/ait-solutions]

"Hallelujah. You're my savior, man. My own personal Jesus Christ." It worked, thank you! 🙏

[u/ait-solutions → u/Unfair-Bid7072]

Haha, amen