Dual GPU not working on x399 Taichi

happyferret wrote: Hi noktek, I was having the exact same issue (except with 2x 1080Ti) last Friday, and spent more than 8 hours fighting with it until uncovering your post: you are not alone. I am running linux, but have the exact same problem of the second GPU being detected, but in my case not being usable by CUDA. I have a "beefier" power supply (1200W gold Seasonic), and have had a very strange reactions to switching power cables around in the computer: - I usually cannot use both cards (more than 99% of the time). - However, sometimes, after I stop the machine, and switch cables around inside, I can get ONE boot where both cards are detected and can be used by CUDA. This does not last until the next reboot, and has worked oince when both cables were plugged with two cables each (and therefore no PSU power to the motherboard), and ONCE when the motherboard was plugged to the PSU (and therefore one of the GPU was connected to only one power cable (in this case, the detected card was under-powered in a way, but was detected and usable). I am sorry if this is confusing, I can elaborate: TL;DR: I can SOMETIMES get both cards to work, but it seems completely random, is very rare, and does not last after a reboot. I am extremely confused. I have updated the BIOS to the latest patch (November 7), but this did not help. I suspect that it is not a power problem, but cannot find what seems to have any effect on this problem. Thanks to anyone with new ideas, I would love to have the two GPUs actually work together :-)

happyferret, is there any chance you would be willing to try W10?  Please flesh out your specifications with drives, memory, SSDs and anything else.  I suspect you you are well aware of how to run W10, but will be glad to give you some pointers if needed.  Thanks and enjoy, John.

EDIT:  Fun User ID!


Edited by MisterJ - 20 Nov 2017 at 5:00am

An HX 1200i should be enough for a TR system and two video cards. This PSU's +12V rail is capable of 100A output. If the PC is drawing over 100A from the +12V rail just booting and at idle, so much for power efficiency of TR:

http://www.corsair.com/en-us/hxi-series-hx1200i-high-performance-atx-power-supply-1200-watt-80-plus-platinum-certified-psu

Switching to single rail will skip the need to balance the power on the +12V rails, but just starting and running the PC should not cause that much of a power draw. 40A on a rail might be a limitation for the CPU, which could interfere with the PCIe lanes, just a thought. But the CPU here has multiple power sources/connections.

I would start over by clearing the CMOS/UEFI, connect all the PSU cables to the board as required, and use one video card. Possibly starting with the 780 alone in the board. Once one card is working normally, add the other. If you've never tried the 780 by itself, that's what I would try now.

I'm wondering if the VBIOS in the 780 SC is UEFI/GOP compatible. It should be if it is an EVGA video card, EVGA went to UEFI compatible VBIOS starting with the 700 series. The 1080Ti will have a UEFI/GOP compatible VBIOS. Since you use a 960 Pro NVMe SSD as the OS drive, the Windows 10 installation should be UEFI booting by default. Windows 10 installed via a USB flash drive?

You lost me on "If i remove uninstall the 780 it then shows up as VGA adapter displaying no errors." That's the Device Manager entry, correct? I assume that is before you restarted the PC? Or does that ghost entry remain after a restart?

I wonder if this issue is related to the early Window 10 RS1 versions and the IOMMU option being enabled, not being compatible. Obviously the Windows 10 installation boots, so you are either using a Windows 10 RS2 version, or have IOMMU disabled.

So the driver version is identical for both video cards? During the installation, are you prompted to select which card is the target of the installation? Or do both cards just get the driver installed? No errors from the installer during or after the driver installation process?

What happens if you run the NVIDIA Control Panel software with both cards in the PC? Can you check how many PCIe lanes are being used by the 780 with that or other software? If you've used two different video cards like this in the past, is there anything you've had to do to get them working?

Usually two video cards don't have a problem with the amount of memory Windows needs to deal with both cards. The UEFI option to change that is usually called Top Of Lower Usable Dram, or TOLUD, setting it to Dynamic. If and where that option is in your board's UEFI, I'm not sure, usually in the Chipset Configuration screen, but could be elsewhere with X399.

Try to keep an open mind about the mother board being the problem. We see that being blamed for issues all the time, and when a new board fixes nothing, which we also see all too often, it's more than just a waste of time.

noktek, I think you need more power, perhaps 1000 Watts.  Hopefully others will comment.  I have 850 W with one video card and a lot less storage.  The CPU can use close to 200 W under load.  I assume drives are TB (Terra Bytes).  Can you borrow a heftier power supply to try or return yours for credit?  If you test with more power and still have problems, then perhaps you have a MB problem and need to talk to ASRock.  I get drivers from only the vendor who makes the product, not other sites.  Have you looked here: http://www.nvidia.com/Download/Find.aspx
Enjoy, John.

hi guys thanks for all the suggestions, it was a hard day of trial and error and nothing accomplished: