Question RX 6600 XT not working in x16 slot on new B660 mobo

Sep 15, 2022
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TL;DR resolution, in case it helps anyone later:

PowerColor Fighter RX 6600 XT does not work in 4.0 x16 slot on the following motherboards:
  • MSI MAG B660M MORTAR WIFI DDR4
  • MSI PRO B660M-A DDR4
Gigabyte RTX 3060 Ti EAGLE works in the Mortar motherboard.





============== original post ===============================================

  • GPU: RX 6600 XT (1 month old)
  • Mobo: MSI B660M Mortar (new)
  • CPU: i3-12100f (new)
Symptoms:
  • RX installed in 4.0 x16 slot works fine via generic video modes (in bios, in Windows without AMD drivers, in Linux with nomodeset)
  • With AMD drivers loaded and RX in x16 slot = black screen in Windows or Linux
  • RX in 3.0 x4 slot works fine with and without drivers
  • RX works fine in 3.0 x16 slot in my previous mobo+cpu (B360M DS3H / i3-8100) - has worked fine for a month
  • RTX 1060 works fine in new board in 4.0 x16 slot
Information:
What I have done:
  • Updated bios and motherboard drivers
  • Used DDU to remove all video drivers (that's how I discovered it works fine without drivers)
  • Tried both latest adrenaline driver (22.8.2) and latest "Pro edition" driver (22.Q2).
  • Set the PCI slot explicitly to 4.0 and 3.0 and 2.0 instead of auto (per some older threads)
  • Pared the system down to just the cpu, gpu, one ram stick, and no drives booting on a live USB - problem persists
  • I put a ticket in with MSI this morning. Haven't heard back yet.
A lot of similar issues found in these forums and elsewhere - many never resolved. I think I've tried the things that worked for others.


Question: Does the 1060 working definitively rule out a motherboard / CPU defect?

Any other suggestions?



Side note - my first time buying a CPU with no onboard graphics - boy I wish I'd spent the extra $15 for debugging!
 
Last edited:
Sep 15, 2022
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brand and model of the psu?
Seasonic X-750

Which works fine under stress testing / benchmarking / gaming with the RX in the old mobo, and supported stress testing/benchmarking of the RX in the x4 slot in the B660, so it not supporting idle power in the x16 slot seems unlikely.

I might run a stress test with the 1060 in the B660 x16 slot since I've only run the system at idle in that slot.

ETA: The new mobo takes two CPU power connectors where the old one takes one, so that's the one PSU-related difference I can think of.
 
Sep 15, 2022
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Sounds like one of those cases where PCie 4 GPU does not want to work on certain motherboards despite all components being fine. The only thing you haven't tried is updating GPU's VBIOS (if possible).
Any thoughts on whether the issue is more likely the GPU or the mobo?

It's a lower-end GPU (PowerColor) and higher-end mobo, so I'm inclined to blame the GPU.

GPU just barely still in return window, and mobo easily returnable.

Also - is this mainly an AMD GPU problem? Past similar posts seem to be AMDs
 
Sep 15, 2022
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Can you set your bios to say the slot is x8? If I recall that’s the pci e speed that card works at.
Yeah it's an x8 card.

Haven't seen a way to set that in bios but I'll look again when I boot it up later.

Just inspected the CPU socket pins and they look fine.
 
Sep 15, 2022
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The RX 6600 XT can only use x8, set it down in BIOS and try rebooting.
The manufacturer requires a x16 size slot for its length, however the GPU is hard-wired at the factory for x8 lanes.
 
Sep 15, 2022
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Added TL;DR at top of original post, but here's the further investigation and resolution:

Tried RX board in MSI PRO B660M-A DDR4 , same failure mode as with the MSI Mortar.

They are very similar boards so I guess they have the same incompatibility, but this gave a strong indication that the original motherboard wasn't broken.

Replaced the PowerColor RX 6600 XT with a Gigabyte 3060 Ti and it works fine.
 
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