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Z77 Extreme 4 PCI-E: Lane Problem
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ranton View Drop Down
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    Posted: 18 Jun 2015 at 4:17am
Hello everybody,

for a few days now, i have major issues with my system. Games started crashing whenever SLI was activated (i got two gtx770). Today i found out, that the first gpu runs on 8 lanes, while the second only runs on 2!

I tried both GPUs in the PCIE Slot 2, which is the first one for GPUS. They both ran on x16 there.
Then i tried the same on the PCIE Slot 3, which then only provided 4 lanes in single GPU mode, which cant be right.

Before i send my motherboard back under warranty, are there any other suggestions? I tried resetting the bios, made an update to it and even installed a fresh OS, which had the same problem. So i guess its no driver problem. I also tried setting the PCIE mode for the slot in the uefi.

And for your information, it used to work for over a year so far.
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Hello and welcome to the forums Smile

Before you send the board off I would try reseating the CPU after cleaning the landing pads on it off carefully. Also have a look for any bent pins in the CPU socket. The PCIE lanes are on the CPU so if there is a problem with lanes that's where I would look first Wink

If that is of no help then it sounds like it could well be a warranty situation though it could also be the CPU, especially if it is overclocked at a high vcore.
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Originally posted by ranton ranton wrote:

Hello everybody,

for a few days now, i have major issues with my system. Games started crashing whenever SLI was activated (i got two gtx770). Today i found out, that the first gpu runs on 8 lanes, while the second only runs on 2!

I tried both GPUs in the PCIE Slot 2, which is the first one for GPUS. They both ran on x16 there.
Then i tried the same on the PCIE Slot 3, which then only provided 4 lanes in single GPU mode, which cant be right.

Before i send my motherboard back under warranty, are there any other suggestions? I tried resetting the bios, made an update to it and even installed a fresh OS, which had the same problem. So i guess its no driver problem. I also tried setting the PCIE mode for the slot in the uefi.

And for your information, it used to work for over a year so far.


What program is telling you that your cards are running at x8 and x2? Is that constantly or under load, or at idle?

The PCIE3 slot is electrically X8.

If both cards worked at x16 by themselves, maybe your SLI bridge is bad. Could also be a power supply problem.
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Hello there,

i dont think its a problem with the cpu, as i has not been moved for almost a year. And it was only slightly overclocked but undervolted.

I am using nvidiaInspector to check the lanes. I first thought of the bridge myself, but the pcie3 slot only gives me x4 when in single mode, which is too low also.

I will try reseating the cpu and changing the bridge.


I also just checked, im a bit confused: It seems like the first graphics card is the one running on x2 whilst the second runs on x8. Am i right if i assume that the first should be the one on the pcie2 slot?

http://img.techpowerup.org/150618/nvidia_20150618_095142.png
http://img.techpowerup.org/150618/nvidia_20150618_095212.png


Edit:

As you notice on the screenshots, i am using an older driver atm, thats because i knew this one worked for me.


Edited by ranton - 18 Jun 2015 at 3:55pm
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That is odd for sure. Can you try with another PSU as Parsec suggested? Also what happens if you stress the cards with SLI active, does the lane usage change or remain as it is in your screenshots? GPUz has a stress option designed to force the GPU/s into maximum PCIE mode, if you can post up some screenshots of this in action that may help to pin down the issue.
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Alright, pretty mixed results here..

I dont have another psu here to test.
I activated sli now, tried the gpuz test, but only the x8 card did anything. The x2 card just idled.
Then i tried fluidmark and made card two physx card. Now both did what they where supposed to, but card two stayed at x2. This sounds a lot like the sli bridge is faulty, doesnt it? Ill have to get a new one and try that out.
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Alright guys, this is one of those things.

I just wanted to double check the cards, put both out, only one back in in pcie3.
Suddently x8. Second card, same result. In pcie2 x16.

Put both in, both on x8, sli working perfectly.

I havent changed a thing, neither hardware nor software. But it works.
It may actually just have been some stupid piece of dust on some contact or something.

Thanks a lot for your support and have nice days!
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Glad you got it sorted Thumbs Up

Poor contact, the bane of electronics Pinch
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Thanks for providing the update, regardless of what the fix was.

That is a great example of what can and does happen. I was ready to guess that one of your cards was bad, running at x2, but that was not the situation.
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