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Connecting graphics card power kills power supply

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Guest

Guest
Hi - just got a new ATI 4870, plugged in both 6-pin power connectors from my 750W supply (which has one 6-pin connector; for the other I used a converter on a spare molex), and hit the power-on. Nothing. The power supply does not even fire up. If I disconnect the 4870 it's all fine again.

Surely 750w is enough? I have two HDDs (one IDE, one SATA) and one IDE DVDROM, which doesn't sound excessive on a 750w supply -and in any case, even with them unplugged from the power I get the same result - it just doesn't like the gfx card.

I got hold of a nVidia GeForce 9800GX2, a beast, and had exactly the same result.

I have a Gigabyte GA-M55SLI mobo. Is there any reason that would be incompatible? These cards are pretty huge.

Would much appreciate any feedback from you guys!

Cheers, Ben Board
 

ohiou_grad_06

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Dec 19, 2006
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Depends on the power supply. What are the specs on it? There are some that I would not trust my system to. It's not wattages you want to look at, you want to look at brand, but also how much amperage the power supply lists.
 

dndhatcher

Splendid
The PSU model would be nice to know. Rails and AMPs may be an issue.

What converter cable did you use for the molex to pcie?

Since you got the same problem with 2 different graphics cards ( I assume you know the 295 was working somewhere else) the power has to be the issue and the molex to PCIE is the likely suspect.

Will the PSU turn on with the GPU seated but the pcie power cables not plugged in? If it will then you know your gerry-rigged plug is probably the problem.
 

dndhatcher

Splendid
The link to the converter cable isnt working for me. - had to remove the period from the end.

The PSU is old. All the amperage is on the now unused 3.3v and 5v rails.
It only has two 20 amp 12V rails, which is more like a modern 500-600W PSU.
A newer 750W PSU would have twice that many amps on 12V rails.

Still it should be enough for a single 4870 (but probably not a 98000GX2).

Did you ever see if the power comes on with the GPU plugged into the PCIE slot, but no power cables? Its possible seating the card is touching some other component and creating a short, but I still think the PCIE plug is the problem.

The converter plugs into two molex connectors. Make sure you use two different cables (not two ends from one split cable) and dont use the same cable as your HDD, CD or floppy. Get that pcie connector the biggest, cleanest power connection you can.


Maybe this will be a good lesson for others. The PSU is the last component of a PC you want to cut corners and save money on.
 

Duesouth

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Mar 22, 2009
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the problem is the amperage, he is lucky that the power just does blow up on him destroy anything that is connected to. I have gone threw 2 corsair 750 also and 2 antec tp3- 750 both 750 each both brand new from the year 2008 december. all four have blown on me and now I have bought the beast of cooler master 1250 watts real power continous. lol overkill but it eliminate all of my problems. brand new can also be a bad batch of production. deja vue for me already posted this comment like 10 times. you need at least a 800watts or psu and brand name well it is up to you what you are comfortable with. just make sure you get got amperage for each rail.


1250watts cooler master overkill but it works like a charm. no problems no headaches. just get rivatuner to cool that beast of video card. it heats my place up when I play games in 1920x1080.
 

dndhatcher

Splendid
@duesouth - A single 4870 GPU system should not need that much. You must have power issues from the wall to blow that many good PSUs up (or you got extremely unlucky with production batches).
 

mindless728

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wtf did you do to those PSU's, both the corsair and antec are great brand PSU's, for a single 4870 you could get away with a corsair 550VX, and for crossfire 2 x 4870's you really only need a corsair 650TX (recommended to have the 750TX just for the right connectors)

and btw, CM is usually not the best PSU maker

and no, he doesn't need an 800w PSU, he just needs a decent 550w (for the 4870)



that could be an explanation, though that means the CM 1250w could go too
 

gomi

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Is your power source stable? if the power coming from the lines is unstable it can fry your pc components. Happened to a dude I know that used to live in Mexico, his mobo fried up because of weird voltages coming from the power lines.
 
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Guest

Guest


Nah, when one or neither of the power cables is connected to the card, it boots up fine (I get a terminal red flashing message telling me about the lack of power).



Ahaaaaaaa. I'm only connecting one of the molexes (moleces?). Good point - I'd subconsciously assumed that I only needed one, didn't really think why there were two.

But now you say I need to find two molex connectors on two power lines, neither of which has a drive on it? In addition to the PCI-e power line coming from the PSU? Holy moley. I don't think I have that many lines. Am I likely to blow it all up?

(Can I just say how bl**dy backward this PC upgrading lark is? It's basically moved on not one inch since I built my first 386 with my Dad in 1990. It's all screwdrivers, tribal knowledge, crossed fingers, and the ever-present threat of PC ruination. It's enough to make me stick wth my Xbox :p )
 

dndhatcher

Splendid
Ahaaaaaaa. I'm only connecting one of the molexes (moleces?). Good point - I'd subconsciously assumed that I only needed one, didn't really think why there were two.

But now you say I need to find two molex connectors on two power lines, neither of which has a drive on it? In addition to the PCI-e power line coming from the PSU? Holy moley. I don't think I have that many lines. Am I likely to blow it all up?
You could take one molex line with 2 connectors and plug both in. Should not do any harm. You dont want to use a line with a CD/DVD because you dont want to be running then overload the rail and shut down when the drive comes on.