View Full Version : Twin 7950 GT KOs in SLI = blank screen

03-29-07, 11:45 AM
My Voodoo died so I built my own machine to replace it. I did cannablize the DVD and DVD RW as well as the two SATA Baracuda drives. Here's the rest:

Antec 900 case
EVGA 680i SLI Mobo
Creative Soundblaster X-FI Fatal1ty SB
2x 7950 GT KO 512M EVGA Video boards
2x 1G K-Byte RAM (rated at 800 which I belive is the 1033MHz FSB speed)

Now, after getting this machine up and running, and using it for about 2 weeks, the old hard drives began to flake out and one of them just just completely failed. Seeing the writing on the wall, I bought a new Western Digital 320G hardrive and installed it. Initially I tried to copy the OS from the old drive to the new one and do a repair install but, the results were quite poor. So, I finally scratch installed the system on the new drive. I got the drivers all installed, the video cards looked fat dumb and happy and then the fun began:

Enable SLI: blank screen.
Power down via 4s hold on the power button and bring it back up. On other machines I've built, when first starting SLI I have had the screen go blank and then recover on a reboot. However, this time, I got the Windows splash screen, but at video mode changeover: blank screen.
Power down and bring it up in safe mode.
Reboot to normal mode: splash screen... blank screen.
Power down and bring it up in safe mode.
Reinstall drivers.
Power down and bring it up in normal mode: splash screen... Logon!
Enable SLI: Blank screen.
Rinse repeat with safe mode and driver reinstall.
Updated drivers. Enabled SLI: Blank screen.
Rinse repeat with sae mode and driver reinstall.
Powered up normal. checked the MoBo BIOs (there was a warning on the NVIDIA web site) all good and up to date. Enable SLI: blank screen.
Got the bright idea of trying another port on the video card and crashed my machine hot plugging the video cables (I work as a test engineer and have yet to see problems with hot plugging cables on video... then again, I test machines worth many multiples of what my home machine is worth). System recovered so I extended the screen to port 2 and the primary screen froze... eventually the system crashed down, then came up to BSOD. Crashed, BSOD... repeat ad nauseum.

At this point I went to bed and figured I'd have to do a scratch install today. yes, I know, hot plugging the cable is risky but, honestly, I really have done a LOT of hot plugging in test at work and have only seen problems hot plugging cards ;> NOT cables... well, wait, there was one very delicate communcations card we worked with (crypto), but, that's another post. Long and short is that the hardware worked fine until I added the hard drive and set it up. Thing seemed quite stable after installing the new drivers, so long as I didn't start SLI. I'm willing to accept that I may have set a circuit bad by swapping the cable on the video card and that likely is the BSOD issue. I'll try yet another scratch install tonight in hopes of fixing -that- issue... having said that, I'll take any advice I can get.

03-30-07, 09:52 AM
Forgot some information of minor, ok major, importance: I'm running Windows XP Pro. Note that this did work before I replaced the hard drive, so, I can't see why enabling SLI won't work now.

Update: scratch installed the system again last night and have it up and running fine save that it still blanks the screen when I enable SLI.

03-31-07, 11:48 AM
you might want to wait a bit when the screen goes blank. it should come back.

04-02-07, 10:26 AM
I now have a clue, and I don't like it.

First off, I got a reply from tech support and as usual they have little or no clue. The suggestion from tech support was to try the second card as 'sometimes the video switches to the secondary card'... this I have never seen and doubted seriously but, gave it a try: no dice. All 4 ports, in fact, were black after going into SLI mode. I rebooted the machine and came up in safe mode where I downloaded 93.71 and loaded those drivers after uninstalling the cards. That was Saturday night.

Sunday, I ran my machine in single card mode. The machine was on for about 12 hours but, I played Vanguard for only about 5 hours. About midnight last night I came in to try Wintons suggestion of enabling SLI and walking away from the black screen... essentially, giving it time to sort itself out. When I enabled SLI, the screen blanked, blinked, the monitor lost connection and just as I was about to get up and walk away... the screen came back to life! I powered down, and then brought it back up as if to prove I was not imagining things and I'll be darned if it didn't come up and, as a bonus, I got the little balloon saying I was in SLI mode.

Note: I did nothing different than anything I've tried before accept possibly letting it be on for a long time before trying it (and I'm pretty sure I've had it on this long before when it failed). What this tells me is that these cards likely have a thermal issue (we all know these cards run more hot than we'd like). What I mean is that after being on for 12 hours, the machine finally decided to enable SLI successfully. Now, I'm not saying NVIDIA has a thermal problem, I'm saying that the combination of the NVIDIA chipset on the EVGA 7950 GT KO is likely at thermal risk... I'll see over the next few weeks and months as I run the cards. So far I've not noted any indications that I'm running anything but in the green, thermally speaking and I've been impressed with the Antec 900s ability to conduct heat out of the case (so far).

Thanks for the assists here folks!