Second PCIe 16X crashing, when system is overclocked

[psolord]

Hey guys.

So I have this very weird problem, which I didn't notice before. I believe it belongs in this sub-forum, since it has to do with system instability with specific GPU setup.

After getting a GTX 970 for my primary rig, I installed my 7950 crossfire on my secondary rig, which now has the following specs.

Case: Thermaltake Armor
Mobo: MSI Big Bang Trinergy
RAM : 2X4GB G.Skill Ripjaws DDR3-2000 PC3 16000 CL 9-11-9-29 1.60v
CPU : Intel Core i7-860
CPU cooler : Noctua NH U12P SE2
GPU : 2X Gigabyte Radeon 7950 Windforce 3 rev 2.0
PSU : Enermax Galaxy 850W

I've been too caught up with testing and playing with the GTX 970 but now I decided to have some benchmarkig fun on the i7-860+7950 cfx system and to my surprise I found out that the system is crashing/halting/freezing when it is overclocked and crossfire is enabled.

I know that dual gpu takes more cpu resources, both because of the dual gpu itself, but also due to the higher performance the system is putting out, but this is not such a case.


I tested both cards on the first slot, when the cpu is running at 4Ghz and they worked fine. On the other hand both cards crash when they are installed one by one, on the second PCIe 16X slot. Actually it's mostly a freeze, that keeps showing the screen I was seeing, but the sound plays normally, although in a loop. The freeze occurs 5 seconds into any dual gpu test.

Still when the system is running at stock clocks, everything is fine.

The settings I am using for 4Ghz are the following.



I am sure you will notice that I am running QPI higher than I should, but believe it or not, my system actually LIKES the QPI at this setting. It has never crashed with a single card, it completed OCCT, it managed 20 runs of Linx and in general it's very stable for the workloads I need it to be.

With a lower QPI setting, it is LESS stable, but I am not sure if thing change in dual gpu mode. This of course will be one of the first thing to try other than reducing clock speed/cpu base frequency until it gets stable.

Keep in mind that this motherboard has a NF200 chip, if that is important. Still it worked fine with my 5850cfx and 570sli configurations years back.

I also thought that there maybe some weird incompatibility with Windows 8.1, because I had Windows 7 before.

In any case, if you can think of something while I try to figure this out, please let me know.

 

[ShintaiDK]

When you overclock via the BLCK you also overclock PCIe and other busses.

 

[2is]

When you overclock via the BLCK you also overclock PCIe and other busses.

iirc, that applies to Sandy Bridge and newer CPU's.

 

[ShintaiDK]

iirc, that applies to Sandy Bridge and newer CPU's.

http://www.anandtech.com/show/2832/19

 

[2is]

I stand corrected, thanks for the link

 

[iiiankiii]

Wait a sec. I remember overclocking an i5 750 just fine. Yes, you over clock thru the blck but the pcie freq was locked. I was using a 2x radeon 6850 with the CPU over clocked to 3.6ghz just fine.

 

[psolord]

Well there is a setting in the pic above, that shows PCIe frequency at 100Mhz.

Still this must not be the problem, because it is the second slot that is crashing.

Whatever I do with the first slot, the system remains stable.

Unfortunately I saw something worrisome today. I started decreasing clocks and voltages, until I reached stock values and the system was still unstable, whereas it was stable before.

I am beginning to fear some deeper damage on the second slot, or the associated circuitry. It is very clean though. No dirt signs anywhere.

Will do more testing come Monday.

Thanks for your time guys.

 

[ShintaiDK]

You may have killed the NF200 chip by PCIe overclocking.

In terms of your PCIe frequency adjustment. The x16 lanes coming out of the CPU is still controlled by the BLCK.