Can't detect second GTX 970 for SLI

[thordurroth]

HARDWARE
Gigabyte GTX 970
MSI GTX 970
Gigabyte Z68X-UD3P (SLI support, 1 Pcie x16 slot and 1 Pcie x8 slot)
i7-2600k (16 Pcie lanes)
750W power supply

The problem
I don't get the option to enable SLI in the NVIDIA Control Panel.
I only see one graphics card under the display adapters in the device manager.

What I know

• 
  ■ I have tried putting both cards in both slots, one at the time and both at the same time.
  ■ The card in the x16 slot works 100% of the time. Does not matter which one is in it or whether there is a card in the x8 slot.
  ■ It never works to connect the monitor to a card in the x8 slot.
  ■ The Gigabyte card has a light that turns on when it is in the x8 slot, even though the power connectors are not plugged in
  ■ Gpuz tells me that the x16 slot is running @ x8 event though there is no card in the x8 slot even though I use the rendering
  ■ I have tried turning off secure boot in the BIOS

Questions
What could I do more?
If the bridge were broken would the card in the x8 slot appear in the device manager?
How can I know if the x8 slot is broken? Should I be able to run a single GPU from the x8 (leave the x16 empty)?

 

[EquineHero]

HARDWARE
Gigabyte GTX 970
MSI GTX 970
Gigabyte Z68X-UD3P (SLI support, 1 Pcie x16 slot and 1 Pcie x8 slot)
i7-2600k (16 Pcie lanes)
750W power supply

The problem
I don't get the option to enable SLI in the NVIDIA Control Panel.
I only see one graphics card under the display adapters in the device manager.

What I know

• 
  ■ I have tried putting both cards in both slots, one at the time and both at the same time.
  ■ The card in the x16 slot works 100% of the time. Does not matter which one is in it or whether there is a card in the x8 slot.
  ■ It never works to connect the monitor to a card in the x8 slot.
  ■ The Gigabyte card has a light that turns on when it is in the x8 slot, even though the power connectors are not plugged in
  ■ Gpuz tells me that the x16 slot is running @ x8 event though there is no card in the x8 slot even though I use the rendering
  ■ I have tried turning off secure boot in the BIOS

Questions
What could I do more?
If the bridge were broken would the card in the x8 slot appear in the device manager?
How can I know if the x8 slot is broken? Should I be able to run a single GPU from the x8 (leave the x16 empty)?

The i7 2600K only has 16 PCIE lanes. That's probably the problem - get a CPU that has more than 16. My Xeon has 20 and I can SLI on a supported board just fine.

It also might be that your CPU only supports PCI-e revision 2.0, where SLI on the Maxwell cards needs 3.0 to work.

 

[thordurroth]

[
The i7 2600K only has 16 PCIE lanes. That's probably the problem - get a CPU that has more than 16. My Xeon has 20 and I can SLI on a supported board just fine.

It also might be that your CPU only supports PCI-e revision 2.0, where SLI on the Maxwell cards needs 3.0 to work.

Thanks for the reply,

However should the graphics card not appear in the device manager even though the sli isn't working?

The following is from the motherboard spec site: "When the PCIEX8 slot is populated, the PCIEX16 slot will operate at up to x8 mode." so I would assume 16 lanes on the cpu should be enough, I'm not using any other pcie slots.

I have read forum posts from people who did gtx970 sli with an i7-2600k. Also the pcie revision is both backwards and forward compatible.

 

[EquineHero]

[
The i7 2600K only has 16 PCIE lanes. That's probably the problem - get a CPU that has more than 16. My Xeon has 20 and I can SLI on a supported board just fine.

It also might be that your CPU only supports PCI-e revision 2.0, where SLI on the Maxwell cards needs 3.0 to work.

Thanks for the reply,

However should the graphics card not appear in the device manager even though the sli isn't working?

The following is from the motherboard spec site: "When the PCIEX8 slot is populated, the PCIEX16 slot will operate at up to x8 mode." so I would assume 16 lanes on the cpu should be enough, I'm not using any other pcie slots.

I have read forum posts from people who did gtx970 sli with an i7-2600k. Also the pcie revision is both backwards and forward compatible.

Yes, but your CPU only supports up to PCI-e 2.0. Motherboard support doesn't matter when your CPU doesn't support it.

If it doesn't show up in device manager the slot is likely broken.

 

[thordurroth]

[
The i7 2600K only has 16 PCIE lanes. That's probably the problem - get a CPU that has more than 16. My Xeon has 20 and I can SLI on a supported board just fine.

It also might be that your CPU only supports PCI-e revision 2.0, where SLI on the Maxwell cards needs 3.0 to work.

Thanks for the reply,

However should the graphics card not appear in the device manager even though the sli isn't working?

The following is from the motherboard spec site: "When the PCIEX8 slot is populated, the PCIEX16 slot will operate at up to x8 mode." so I would assume 16 lanes on the cpu should be enough, I'm not using any other pcie slots.

I have read forum posts from people who did gtx970 sli with an i7-2600k. Also the pcie revision is both backwards and forward compatible.

Yes, but your CPU only supports up to PCI-e 2.0. Motherboard support doesn't matter when your CPU doesn't support it.

If it doesn't show up in device manager the slot is likely broken.

Yeah, the slot might be broken :/ I'm gonna investigate that hint further. I've never put anything in it before but both my original GPU and memory died on my 2 years after I bought them.

If a CPU only supports PCI-e 2.0 then the Gpu and mobo just adjust to that speed. Should not be a problem. It is just a matter of data rate not actual compatibility.

 

[EquineHero]

[
The i7 2600K only has 16 PCIE lanes. That's probably the problem - get a CPU that has more than 16. My Xeon has 20 and I can SLI on a supported board just fine.

It also might be that your CPU only supports PCI-e revision 2.0, where SLI on the Maxwell cards needs 3.0 to work.

Thanks for the reply,

However should the graphics card not appear in the device manager even though the sli isn't working?

The following is from the motherboard spec site: "When the PCIEX8 slot is populated, the PCIEX16 slot will operate at up to x8 mode." so I would assume 16 lanes on the cpu should be enough, I'm not using any other pcie slots.

I have read forum posts from people who did gtx970 sli with an i7-2600k. Also the pcie revision is both backwards and forward compatible.

Yes, but your CPU only supports up to PCI-e 2.0. Motherboard support doesn't matter when your CPU doesn't support it.

If it doesn't show up in device manager the slot is likely broken.

Yeah, the slot might be broken :/ I'm gonna investigate that hint further. I've never put anything in it before but both my original GPU and memory died on my 2 years after I bought them.

If a CPU only supports PCI-e 2.0 then the Gpu and mobo just adjust to that speed. Should not be a problem. It is just a matter of data rate not actual compatibility.

A PCI-e 3.0 card running at 8x is running at the same data rate as a 16x 2.0 card...think about that...