Twin 6800 GTs in SLi

Question

Hi folks,
I've got myself the  ASUS K8N-SLi Deluxe board and have popped two of these in it:
http://www.scan.co.uk/Products/ProductInfo.asp?WebProductID=154668
(MSI 6800 GTs)
after *alot* of testing & playing and mucking about I still cannot get them to work satisfactorily in SLi mode.
Picture Shows it best (Far Cry)
Link
There is distortion of one half of the screen (Show GPU balancing is enabled to show that it is the output of one card).
This distortion is not seen when captured direct from DirectX (Fraps)
Link (Warning: large Files, sorry)
Board is the A8N-SLi Deluxe (BIOS REV 1002), Athlon Fx55, MSI Gf6800GT x 2, 550W PSU
tried:
swapping cards round,
cards individually (fine)
dicking around with memory (dual channel on and off etc)
unplugging all optical drives / fans to free up power
nvidia drivers 69 - 71.20 (no change)
E-Z Plug is in place, E-Z Selector configured for dual cards, SLi connector in both orientations
other apps (HL2) show similar, although seem to implement SLi in another way, as the interferance appears in a different fashion on the screen (flickering on and off, scrolling up / down the screen)
at lower resolutions, the effect is not quite so bad and appears as simply a distortion on the lower half of the screen when the cursor is moved over / there is movement on screen.
In Single card mode everything is fine also
If you run a game in SLi mode, BUT windowed, there is also no distortion effect.
Some other people are having this problem:
Anantech Forums
(Last Starfighter is me
and
Link
but Asus insist that the fault lies with the MSI cards:
Quote
Dear Alex,
This is more likely to be related to the graphics cards themselves. Try the latest Nvidia drivers or check with MSI.
UK Technical Support
PLEASE DO NOT REMOVE PREVIOUS MAILS
WHEN REPLYING AS WE CANNOT GUARANTEE YOU
WILL ALWAYS GET THE SAME PERSON RESPONDING
Any ideas chaps?

Answer 1

[Whoops - lagging a bit. This is for the pre-PSU posts.]
Alex - *Weird*. Looks like the final presentation blit is sorting everything out. I'm hazy on how some of SLi works with this kind of thing. It's also possible that in full screen mode the app is trying to do something which the driver can't handle in SLi - overlays or some kind of palette fiddling, maybe? Just a thought. I don't know if there's a way to fiddle the driver settings to disable the caps for something like that, which might help. (I'm guessing, I don't know my way around nVidia drivers.)
Zoomee - well, it's probably not cut down, for a GTo card.   I suspect they just didn't know. Given the trouble I've had getting anything out of MSI UK (who *also* don't seem to know anything, I don't think that they're being deliberately unhelpful) I believe Scan's technical support when they say they're also unable to find anything out. I've not seen the GTo card specs anywhere on MSI's global site either, and I did try to look before buying it - MSI UK probably should have told me (while I was getting them to find out about the dual link issue) if they'd known.
It sounds like MSI could do with publishing some more information on the things they're shipping, but at the moment I'm too well-disposed to them for actually producing a dual link card (unlike, e.g., Innovision, who *still* say their card is dual link in spite of my contacting them twice, over several months, and finding out that it's not; for some reason their Ultra seems to have lost some pipes, too) to complain.
It would help if nVidia would actually mention any details about the 6800 variants on their web site, of course. There's nothing at all I've found about GTo or LE cards, and very little to distinguish the others.
I thought Scan's site still says 16 pipes (they just quote the 6800GT specs); someone was kind enough to mention that it's 12. I actually posted a query on that before finding out (still being processed, along with the following one saying "ignore me, and you'll be getting your cards back"). Generally, I find Scan to be very good until something goes wrong, at which point they get very confused. It's a gamble. I suspect someone who knows what they're doing is in the background at Scan, but everyone else is running by puppetry, and occasionally the strings get tangled.
At least I now know why 3DMark05 wasn't smooth the whole way through...
I'm keeping my fingers crossed for Overclockers. To be fair, it's not January yet (and my PCI-E motherboard won't turn up until then anyway).  Again, it's unlikely to be their fault if things run late. The only reason I'm looking at GTs is that I've given up on Ultras appearing any time soon - but I need a dual link connector (which means the MSI GT/GTo or I'm into Quadro territory), and I could really do with both SLi and decent generic shading rate. Under Linux, with no SLi (I presume?) for now, it's even more important that the basic card is fast.
At least I've not pulled my current Opteron apart yet; it's only my desk that's a rat's nest of cabling.
I guess we should have realized that 6800 availability was going to be a problem when the die size was first announced. I was kind of hoping they'd have given it a die shrink by now, though (I was expecting the Quadro 4400 to be on a smaller process, but then I was expecting it to be released before now...) and fixed up things like the video decode. The problem with the flagship silicon is that, for marketing, it's wonderful to produce a small number of them and then completely ignore them while 6600GTs get shipped to the masses. Sigh.
I've heard good benchmarks for the Radeons, but I really want PS3.0 and dual link (and SLi helps) so I've ignored them. Good luck if you go that route - you'll never reach SLi speed that way, though. Gigabyte's card with two 6600GTs in one slot
might be worth a look, if it's available yet (you can't SLi it, though).
Thanks for all the information, guys - I'd have had a rude shock some weeks too late if I'd not lurked here...
Er. Alex, I really *hope* that PSU copes. I've only just upgraded to a 480W
Tagan (although it's under-specced), and I'm expecting that to handle it.
Andrew