Asus A8N-SLI no video in single mode

[stebog]

Anyone have any ideas what might be causing the following?

AMD 3200+
A8N-SLI board
7800GT evga
1 Gig Corsair XMS

Both of our systems are identical with the exception of HD's and now I'm running a 7900GT.

My brother bought the SLI board from Newegg. I gave him the 7800GT that worked fine in my system with the same model mobo.

When we installed the upgrade in his computer, we couldn't get video when the selector card was installed as SINGLE. Moving the card to DUAL allowed us to get video and it runs fine. Although there probably isn't a performance bottleneck, it's bugging me that we aren't able to run in 16x mode when in fact it worked perfectly in my system.

Do you think we have a mobo problem or a card selector board problem?

 

[dawza]

When the selector is set to "single," do you fail to get a video signal whether you use the top or bottom PCIe slot? Can you utilize either slot when the selector is in "dual" configuration? As I understand, the selector in dual simply splits the 16x between the two slots so that they run at 8x each; in single mode, one PCIe slot receives the full 16x bandwidth and the other receives 1x, but I believe you can use either slot and run at 16x in single configuration.

If you can run in 16x in one of the slots only, I would suspect a slot problem (especially if you get a POST code for no video). However, it is difficult blame the mobo/slot if you can run in either slot at 8x. If you can utilize both slots in 8x, but not in 16x, it could very well be the selector. Have you tried the selector from your mobo (or tried his A8N-SLI selector on your mobo)?

Either way, I doubt you will see any real-world performance degradation with 8x (do benches and games run OK?). However, your brother did pay for a fully functional board, so an RMA may be in order. Perhaps contact ASUS support and see what they have to say?

Hopefully it is a bad selector chip, which would be a relatively painless thing to replace ($5.00 on ASUS' website, and I am sure they would ship you one for free).

 

[stebog]

It didn't occur to me to try the second slot, so I have no way to answer your question. I have it set in dual mode now with the video card in the primary slot, I was worried about whether or not my brother would have a problem if he were somehow able to find another 7800GT for SLI. I guess I was looking for some assurance that we wouldn't be RMA'ing a mobo the day we try to add another video card.

Man, the 7800GT supplies dried up quick. Wasn't one of the selling points of SLI was the ability to add a second cheaper card later?

Thanks for your help....again. BTW, I received my mobo heatpipe yesterday. I'll be digging into my system this weekend too.

 

[dawza]

Try a simple experiment to see if you can isolate the selector card as the culprit-

Your selector card in your brother's mobo. Single configuration. If your brother's selector card is to blame, then the selector card from YOUR mobo (which we know functions just fine), when plugged into HIS mobo, should allow him to run his 7800GT in single config, at 16X.

Your brother's selector card in your mobo. Single configuration. If your brother's selector card is to blame, then HIS selector card in YOUR mobo should prevent you from running the 7800GT in single config, at 16X.

You will probably want to use the same card (the 7800GT) for this test, to remove the video card as a variable.

SLI = Great idea in principle, but the economics of going SLI depend heavily upon how much your cards were purchased for and how much they will be worth when you try to sell them off. For example, I bought my 7800GT for $270. Assuming I went SLI for another $220, my total cost would be $490. In six months, when I try to sell both cards, how much will they be worth? If I can get $150-180 for each, my net loss will be $130-190. Now, if I instead sold my 7800GT today for $220, and used that to buy an X1900XT for $440, my total cost would be $270 + 440 - 220 = $490. In six months, when I try to sell the X1900XT, I might get $270-300, for a net loss of $190-220. This would make SLI seem the better choice, but only if my projections for resale value are roughly correct.

Anyway, good luck on the mobo and let us know how the heatpipe installation goes.