SLI Woes with PCI xpress

[2sl0w]

i posted this on the dell xps forums here :
[link=hyperlink url]http://www.dellcommunity.com/supportforums/board/message?board.id=Tech_Talk_XPS&thread.id=33351[/link]

But i havent really gotten much help the problem is the cards wont both go in to pci express 16x only 1 will with the other one fluctuating from 1x, 4x , 8x. on 4 up i can play at 8x it is pretty good.. 4x kind of sucks,, 1x is like less than 10 fps and breaks my heart. any suggestions?

 

[Lafinass]

Here's my two cents.

This problem sounds like one of two issues.

The most likely one is that the motherboard is not receiving a consistent enough power flow to maintain both slots at 16x. Try unplugging all non-essential peripherals and see if the problem resolves itself. If it does, you need a stronger PSU.

Less likely, but distinctly possible, is that your motherboard is faulty. Frankly, I know nothing about the dell XPS series so I really have no advice one way or another on that.

Either way, it is very unlikely that this is any issue with the cards themselves. As long as the chipset is the same, they should work in SLI no matter the brand or model. The card with the slowest clock should be in the second slot and the system will throttle down the faster card to match.

 

[Flippy the Squirrel]

I used to work for a computer company, and Lafinass's first scenario is most likely the cause. There was an instance where we shipped a computer with a PSU that couldn't power all of the hardware inside at the same time. As a result, whenever someone connected to the internet, their modem would consume too much power, and the system would reboot. Hilarity ensued.

 

[2sl0w]

hmm i will try disconecting th e cdrom and second hard drive then. you think dells 700 watt power supply isnt enough?

 

[Lafinass]

I haven't the faintest idea. Wattage isn't all that matters and just because it's advertised at 700 watts doesn't mean it can provide that reliably. All I know is that the 8800 series are freaking hogs. I've got an Enermax Galaxy 1000W in mine.

But you said that each slot works fine individually, it's just when both cards are in there. That sounds like insufficient power to me. And in my experience Dell builds their systems to the bare minimum. So it's distinctly possible they'd put a PSU in your system that was capable of running your system as they built it, but not capable of handling a second video card.