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Underpowering 3870's ?

Last response: in Components
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January 9, 2010 6:40:06 PM

Well I have upgraded my system from A 7750BE Dual core to a Phenom II 955BE and overclocked it (Stable prime95) to 3.6 . I got my second 3870 back from RMA today and put it in. I originally upgraded because of horrible lag in games in crossfire. One card alone was running just as good if not better than crossfire. With either processor, With one card in I could run MW2 maxed out really well, but it would have random bad lag spots when turning around real fast, etc. And with both cards in with either Processors in, whenever I looked out into a map, it would just absolutely lag down to around 6 fps, I have to look up at the sky and it goes back to normal. If I look back down, it just lags again. And almost the same the in cod4 when in intense action. I was really hoping that it was just the old Dual core lagging the cards behind, But after today, I'm scoring about 4,000 more than with the 7750 14500 - 18500 in 3dmark06 but absolutely no difference in games. And I just don't get it. So I am wondering, Do you guys think it is the power supply, slowing the cards down? This is my PSU here

http://www.newegg.com/product/product.aspx?Item=N82E168...

Mine is just an older version of it, they changed the way the modular cables connect to it. I have no idea how many amps a single 3870 requires, so I don't know if the power supply can run them or not.

Specs:

Phenom II 955 BE @ 3.6
ASUS M4A79 Deluxe
2gb Corsair DOminators DDR2 1066
2 x VisionTek HD3870 512mb OC edition
Lian-Li Lancool PC-K58W
Western Digital Caviar Blue 320gb
Windows XP Pro SP3 32-bit (Fresh Install)
All games Fresh Install

Thanks in advance :bounce:  :pt1cable:  :love: 

More about : underpowering 3870

January 9, 2010 9:19:04 PM

Tried it and still didn't work. I can hear my fans, when in game are fine, then when it starts lagging down to like 6 fps I can hear the fans kinda dimmer a little. This is only a week old install of XP, and when it was doing it on the 7750BE it was on a clean install of Win 7. As long as the power supply isn't it, I heard somewhere its a recommended atleast 25 amp per rail for the cards, And On this psu it says it only has 12 on two and 16 on the third I think.
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a b ) Power supply
January 9, 2010 9:55:57 PM

coolmax aint they greatest of psu's
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January 9, 2010 9:57:27 PM

not at all lol, least I dont think
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January 9, 2010 10:25:15 PM

^ Thats the CUG, mines CU or CUB, and the CUG is the only one even certified on ATI's list of Power Supplies for alot of crossfire cards. I took out one card, and was getting the same FPS with both cards is, but without it lagging down to a constant 6 fps till i have to leave game. Gottab e something here. New hard drive, new ram new mobo new CPU case and Fresh install of XP and 1 brand new card. Guess I'll just go the the corsair 750W and see if it solves the problem :( 
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a b ) Power supply
January 9, 2010 10:45:44 PM

that should be it since everything else is new
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a c 243 ) Power supply
January 9, 2010 11:05:02 PM

obsidian86 said:
coolmax aint they greatest of psu's

All but the one :) 
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a b ) Power supply
January 9, 2010 11:10:57 PM

that one aint the 700 watts :lol: , is it like coolmax season or something there seems to be a lot crawling out the woodwork lately
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a c 243 ) Power supply
January 9, 2010 11:16:51 PM

obsidian86 said:
is it like coolmax season or something there seems to be a lot crawling out the woodwork lately

Yeah, I noticed that too.
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January 9, 2010 11:20:58 PM

I just don't think it has enough amps per rail 12,12,16 to drive even a single card let alone two. It's supposedly suppose to combine the rails for up to 50 amps when needed (As said on/In box) And as alot have been saying its a lie. A I've seen a couple trying to run a GTX295 with it and the computer will just shut off.
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a c 243 ) Power supply
January 9, 2010 11:35:59 PM

uppercutx said:
I just don't think it has enough amps per rail 12,12,16 to drive even a single card let alone two. It's supposedly suppose to combine the rails for up to 50 amps when needed (As said on/In box) And as alot have been saying its a lie. A I've seen a couple trying to run a GTX295 with it and the computer will just shut off.

1) 12+12+16 = 40 , so there's no way it could combine for a total of 50.
2) There's very few power supplies that can actually output the sum of thier rails.
3) Combined ouput means different things for different power supplies.
Virtual rails are created via an OCP circuit.
If OCP is inactive or set extremely high, you basically have a single rail power supply ( Corsair HX620 is an example )
If OCP is active and set to the rating, trying to pull much more than what the rail is rated for will cause it to go pop.
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