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GTX780 ACX SC unstable performance on MVIE Slot 3(B2)

MetroRat
Level 7
I have experienced some issue with this motherboard. The third PICE slot from the top, aka PCIe 3.0/20_x8_B2, is causing any graphic card that sit on it performing poorly. I noticed this issue when my two GTX780s in SLI configuration, installed on slot 1 and slot 3 as Asus suggested, gave me poor performance in a random pattern. 2 out of 10 system restarts its benchmark results would go very low than it should, meanwhile the CPU would also be busy occupied by system interrupts, making browsing the internet painfully slow. To narrow down the cause of this issue, I reconfigured the SLI to slot 1 and slot 4(at a disadvantage of not using the native PICe lanes of the chipset) and restarted and tested the system for 10 times. Everything turned out to be fine which eliminates the possibility of bad graphic card/driver. Then I put a single graphic card on slot 1 and tested 10 times, no problem. However, when I put the same card on slot 3 and tested it for 10 times, the poor performance issue appeared again in the same pattern as it was in SLI slot1 and slot3 configuration.

Does anybody here have this kind of issue also? Or should I contact the seller for a replacement?

BTW:My power source is AX1200i, and I'm testing it using dual EVGA ACX 780SC with the case open to keep them under 75 celsius degree.
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HiVizMan
Level 40
RMA the motherboard as it is clear you have a PCIe lane that is not functioning correctly.

But before you do so, please go into BIOS and set the PCIe lanes to Gen2 from auto and see if that fixes the issue for you.
To help us help you - please provide as much information about your system and the problem as possible.

Shamino
Moderator
hi you should try to see if gen3.0 instability first
go bios System agent, nb pcie set links speeds from auto to gen2

Sorry to hijack the thread but I'm experiencing a similar issue with my Maximus VI Extreme: Titans in slot 1 and 3 (following the recommendation in the user guide) and a sound card (Phoebus) in slot 5. Horrible performance/stability issue when running game/bench with link speed set to auto. I was thinking it was related to the sound card but the issue remains event when it's not installed.

I followed your advice and set link speed to gen2 and now everything is working perfectly.

Could it be a simple issue that will be corrected with an updated bios (currently running BIOS 0605) or should I simply RMA the board with the reseller?

MetroRat
Level 7
Thanks for your advices. Unfortunately, the problem persists after setting PCIe to gen2. The seller being very amiable, a replacement is already on the way. I will update whether the new one performs differently as soon as it arrives.

HiVizMan
Level 40
Cheers metro let us know how it goes please.
To help us help you - please provide as much information about your system and the problem as possible.

Shamino
Moderator
you can try setting in tweakers paradise clock crossing vboot, clock crossing reset and clock crossing voltage all to 1.55v

Shamino wrote:
you can try setting in tweakers paradise clock crossing vboot, clock crossing reset and clock crossing voltage all to 1.55v


Thanks for you help. I just tried with clock crossing vboot, reset and voltage all at 1.55v and all cards are detected properly (2x graphics card + 1x soundcard) but SLI performance is really bad (choppy, major slowdowns) when everything is set to auto again.

Looks like HiVizMan is right about the issue with a PCIe lane that is not functioning correctly.

Update: I have requested an RMA from the reseller (They are always good about this kind of issues) but while I'm waiting for confirmation, I'll try other suggestions.

MetroRat
Level 7
My replacement board has just arrived. It doesn't work well either. At first I almost thought this board was ok, when it gave me a fair score on Heaven 4.0 with a single GTX 780 ACX SC on slot 3. However, after I restarted and benchmarked the computer for the 7th time, things began to go wrong: more and more frequently, when the computer restarted, it gave no video signal output with the on board VGA_LED in red. Though without video signal, it could still load windows 8 and perform normal shutdown when I pressed the power button. On the other hand, in dual card configuration(slot 1 and slot 3), the card on slot 1 worked well and always gave me signal output, but half the time after restart the second card on slot 3 would go missing on the Nvidia Control Panel.

Later, I spent 2 hours and tested each graphic card individually on slot 1, slot 3, and slot 4 for 10 times. It turned out that things would only go wrong on slot 3.

I am done with experimenting for the moment, and using SLI in slot 1 and slot 4 to get by. Hope some smart guy would stumble upon this thread and help me figure it out.

HiVizMan
Level 40
Hello mate - I have bumped this up to the BIOS and engineers to look at.
To help us help you - please provide as much information about your system and the problem as possible.