MP 7,1 RTX 3090 Founders Edition in 2019 Mac Pro

[Stairway]

I had been running my 7,1 Mac Pro with a single W6800X (non-duo) MPX card in slot 1. I added an RTX 3090 FE into slot 3, and connect the aux power connectors (2 x 8-pin). When I try to boot, the power supply amber light comes on, and the top amber light is flashing the code for "PCIe card error". Then I replace the slot 1 card with my W5700X MPX card, and the machine boots without issue.

Before I start playing around with card swaps, I figured I'd ask here first --- does this sound like a power draw issue when using the 6800X MPX card? Something else?

Thanks!

 

[Stairway]

UPDATE: Moving the RTX 3090 card from Slot 3 to Slot 4, fixed the problem; system now boots without issue when then the 6800X MPX module is in Slot 1.

 

[startergo]

That is interesting. Slots 1 and 3 are supposed to be independent 16 lanes slots:

• As explained above, slots 1 & 3 each have 16 lanes of PCIe 3.0 directly linked to the CPU. Indeed, as these slots are meant to host the graphics cards, you don't want them to have to share the bandwidth with other devices.
• Slots 2 and 4 share 8 lanes of PCIe 3.0 with the MPX connector. These 2 slots are used to provide PCIe bandwidth to the Thunderbolt ports that are available on the card. If you connect a "simple" graphics card only to slot 1 or 3, slots 2 and 4 should be available to provide 8 lanes of PCIe 3.0, that will be part of the 2 pools.

So you only get 8 lanes in slot 4. What is it showing in the Graphics under About this Mac?

Mac Pro (2019 - Intel): Limits and possibilities of PCIe slots

The 2019 Mac Pro allows to connect PCIe cards. Apple gives some recommendations on how to install and configure them. But below are some more recommendations. How to open the "Expansion Slot Util...

softron.zendesk.com

 

[Stairway]

In System Report, bothe video cards show up as x16.