Swapping Titan and GTX 780. Bios won't boot.

[JulioCayetano]

Hi,

We're installing a new workstation today, a threadripper 2990wx, and everything seems to be working as expected. But:
We're using an old Nvidia Titan GPU from our other workstation (AMD 1950X). It seems to work fine in the new 2990wx as it was doing in the 1950X. Now, we're trying to install in the 1950X WS, an old Nvidia GTX 780 (that was working perfectly in an Intel i7-5960X workstation until this morning) to substitute the Titan GPU that was installed. The big issue is that  the 1950X won't boot now with the GTX 780 installed, not even get to the BIOS.
If we install the Titan again in the 1950X WS, it will boot and get to windows normally.

Specs of the 1950X WS:
AMD threadripper 1950X, no OC.
Asus ROG Strix x399-e gaming
128mb DDR4 gskill f4 3000ghz CL14
PSU Prime Ultra 1000 titanium
Cooler CPU noctua NH-u14s TR4
Case corsair Carbide 600Q

Can anyone help us a bit with any ideas of what is happening? We have tried to reset the MoBo memory (CRT RAM I think it was called), shortcircuiting a couple of pins on the MoBo following instructions on manual, but it won't work.

 Thank in advance for your help!

[Juraj]

Interesting thing is, that when you google (GTX 780 won't post for example) you'll get million of results. Looks pretty common.

One wild guess from me, if you already tried multiple PCI-e slots is to set those slots to exact lanes configuration your card is. IE:

1) Put back your Titan if you can't boot without any GPU (if you can ignore this step)
2) Go to your PCI-e slots configuration and set them up from "auto" to what your exact 780 model is (x8 or x16 probably). Try to seat it into that slot.

[JulioCayetano]

Thanks for the idea Juraj,

We've already tried a couple of PCI-E slots, of course, no difference. But, those two we've tested were equal (16x I think). The MoBo gives a Q-code error 94, that the manual says it's related to PCI slots, so you may have your point about that. Tomorrow morning I'll give it a try when back to office.
Thanks!

[JulioCayetano]

Good morning,

We just gave a try to Juraj´s idea and it seems to  work. I didn´t find the way to adjust the speed of a specific slot, so we just changed the general PCI-E CPU link mode from Auto to Gen2, and voila, the PC will post normally with the GTX 780 installed.

This is the exact parameter in our Asus MoBo: Advance/ onboard devices configuration/ CPU PCIE link mode: "Auto" to "Gen2".

Not sure what this means though, are we gonna lose much speed when working in MAX´s viewport, Photoshop, etc.? Should we  change back to Auto or Gen3 and try to tweak other parameters?

Thanks!

[Juraj]

While I can't vouch for why your particular 780 would work under 2.0gen protocol, it shouldn't bother you. It is still using up to 16 lanes and the practical difference should be less than 0.01perc. That is with gaming, the difference in Viewport or PS should non-existent.

[JulioCayetano]

Sounds good enough for us, no gaming expected.

Thanks a lot!