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Mobo won't post with two 470gtx

Here's what I have currently:

Asus P5N-E nForce 650i with an e6750
4x 1G DDR2 800
2x 350G HDD, 1x 1TB HDD
800w psu
evga 470gtx 1280

I've been slowly building towards a new pc, picking up components when I have the money. I'm saving the new cpu/mobo/ram purchase (since they all have to be at the same time) until later this year, probably at the end of the summer.

However, I recently picked up a matching 470gtx since I'll ultimately want to run 2 in my next system, but I also thought that I could run them in my current system as well.

So, here's the problem...

I can insert either gpu by itself on my mobo and my pc will boot fine. However, when I flip the sli selector card to dual and plug them both in, my pc won't post, no display at all, and I get 1 long beep followed by 3 short beeps - which ASUS says indicates a video issue. I've tried unplugging everything but my main HDD and the 2 gpus, removing all but 1 ram stick, etc. but it just won't work with the 2 cards.

From looking around on google, I'm thinking it's one of two things. Either my psu isn't cutting it (I have 2 separate 12v rails for pci-e, one at 20A, one at 22A) or my mobo is having issues. Each 470gtx requires 38A, so I'm guessing I would probably be at the psu's limits, but I think it should at least post. I've also read many threads by people with the Asus P5N-E having trouble running a variety of different cards in SLI. It is an older board, and really not ideal for 2 of these giant cards.

I just wanted to get some opinions on whether it's the psu or the mobo or something else entirely, or if anyone has had any experience with this mobo running 2 newer power-hungry gpus.

Thanks!
6 answers Last reply Best Answer
More about mobo post 470gtx
  1. id say the psu is your problem.
    which one do you have?
  2. It's a realtively cheap XION 800W Real Power, not the modular version.
  3. hmmmm... something tells me it may be a power supply problem.
    you said it works with one 470 but not both of them together.
    i guess your psu is JUST not powerful enough.
    would you like a suggestion of what psu to get? (and where to get it from. eg newegg, amazon, etc)
  4. Best answer
    Though the SLI zone lists "certified PSU's as low as 700 watts for twin 470's, two 470's really want an 850 watter if you OC'ing.

    http://www.slizone.com/object/slizone_build_psu.html

    I'd suggest the XFX Black Edition 850 at $130 as the cheapest of the 1st tier (10.0 performance rating on jonnyguru.com_ PSU's.

    http://www.newegg.com/Product/Product.aspx?Item=N82E16817207001
    http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story5&reid=184

    unless you have an Antec 1200, P183, P193, or DF-85 in which case I'd suggest the CP-850 ($120)

    http://www.newegg.com/Product/Product.aspx?Item=N82E16817371024
    http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story4&reid=142
  5. Thank you for your thoughts, guys. So, if I were to go ahead and get a new psu now that would ultimately go into a newer system this fall with an i7 SB or similar, should I go ahead and go with a solid 850W psu, or something with more punch?
  6. Best answer selected by dwalsen.
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