z790-e gaming only boots from one GPU

[renatojf]

Hey guys, recently built a brand new machine and I have 2 gpus (4060 and 4090).

If I plug the monitor cable in the 4090, it boots fine. If I plug the cable on the 4060, it simply doesn't boot and I am stuck with no signal on the monitor. The computer turns on.. all lights, butt no signal from the 4060 😞

If I unplug the 4090 from the PSU, than it boots from the 4060.

I ran out of ideas. Anyone knows what could be wrong?

[renatojf]

I really need some help here 😞
I tried configuring the BIOS primary display to AUTO, PEG and PCIe. None work. There doesn't seem to be an option to forcefully chose GPU2 as the primary one, so I am kinda lost here. If this can't be done, my whole setup is lost 

[Nate152 · Accepted solution]

Hello renatojf

This looks to be a limitation of the motherboard.

The ROG Strix Z690-E Gaming Wifi has three pcie x16 slots.

The first pcie x16 slot operates at x16. (Using the M.2_1 slot drops it to x8)

The second and third pcie x16 slots operate at x4 from the chipset.

Nvidia gpu's need at least x8 lanes to function.

[renatojf]

Hey @Nate152 thank you so much for your reply! It definitely makes sense, but I am still trying to understand what's going on. Technically, the PCIe 5 16x top slott only shares lanes with the m2 slot. And if I unplug the top slot, the bottom PCIe 4x works, cuz my setup boots from the 4060.

Do you think it is sharing lanes, even tho it is not specified on the manual? I am confused on how it is possible than for the GPU that requires 8x lanes, work under the 4x slot if the first one is unplugged

[Nate152]

That confused me too because normally Nvidia GPU's need x8 pcie lanes to run.

This is a good question to ask Nvidia, they have an online chat.

Click the link and scroll down to the middle "Live Chat".

Support Home Page | NVIDIA (custhelp.com)

[renatojf]

Just spent 30 min with them on the chat @Nate152 

They are clueless as well. Technically it only works on x8 and shouldn't work on x4. Which makes me believe the Asus manual is wrong or shady for this MOBO. It definitely share lanes between x16 and x4 slots, or else I wouldn't see it booting from slot 4.0 x4 with a 4060

They told me to contact MSI support which I don't think will help at all