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My (Early 2008) Mac Pro Video Card Question

boodaddyz

boodaddyz

macrumors member
Original poster
Dec 25, 2008
63
2
Hello,

I have an early 2008 MacPro with a 980W power supply. I am wanting to get two Radeon 7950's. Can my Mac Pro run two of these cards with the current power supply?

I currently have the Nvidia 8800 and it only has 1x 6 pin connected to it, but the 7950 requires two 6-pin each. I believe i would need a slitter. Is this correct?

I appreciate your time, and any advice or help you can offer.

Thanks!
 
NOTNlCE

NOTNlCE

macrumors 65816
Oct 11, 2013
1,087
476
Baltimore, MD
The Radeon takes two 6 pin inputs, which exist on the logic board via Mac Pro to 6 pin adapter, and (correct me if I'm wrong) but the most power you can route from the Optical Bay is two Molex. In theory, it should work, converting both Molex to 6 pin, with no Optical Drive. However, this is just what I'm observing, someone more experienced with this should weigh in here.
 
DanielCoffey

DanielCoffey

macrumors 65816
Nov 15, 2010
1,207
30
Edinburgh, UK
You can run ONE 7950 off your internal PSU, not two. If you use splitters you will run a very serious risk of burning out the traces on the logic board if you attempt to run two 7950s off the same two 6-pin power leads.

You will need to investigate secondary power supplies, either external or in the spare optical drive bay.
 
NOTNlCE

NOTNlCE

macrumors 65816
Oct 11, 2013
1,087
476
Baltimore, MD
DanielCoffey said:
You can run ONE 7950 off your internal PSU, not two. If you use splitters you will run a very serious risk of burning out the traces on the logic board if you attempt to run two 7950s off the same two 6-pin power leads.

You will need to investigate secondary power supplies, either external or in the spare optical drive bay.
Click to expand...

There we go, that corrects my statement. You still may be able to route power from the Optical Drive, but I don't think two molex are going to power a 7950.
 
boodaddyz

boodaddyz

macrumors member
Original poster
Dec 25, 2008
63
2
DanielCoffey said:
You can run ONE 7950 off your internal PSU, not two. If you use splitters you will run a very serious risk of burning out the traces on the logic board if you attempt to run two 7950s off the same two 6-pin power leads.

You will need to investigate secondary power supplies, either external or in the spare optical drive bay.
Click to expand...

Really appreciate the help. Here is my problem. 7950's are very scarce right now, so I ended up getting a R9 280x. I did not see that it required a 6 pin and 8 pin connector. (Thought it was 2x 6 pin)

It comes with a 4 pin molex to 8 pin adapter. Can I unhook one of the super drives and take the 4 pin molex and connect it to the adapter that the video card comes with? I have extension cables to make it longer. Below is an example of the adapter the video card comes with. Appreciate your help.

molex-eps.jpg
 
NOTNlCE

NOTNlCE

macrumors 65816
Oct 11, 2013
1,087
476
Baltimore, MD
I would imagine that would work, that's what I was talking about in my first post. The logic board carries two six pin power adapters, you don't want to run adapters off those, because you will fry your board, like DanielCoffrey said. Give it a shot, I don't know how well the cards work under OS X.
 
ryan42

ryan42

macrumors 6502
Dec 3, 2003
299
0
Near Houston, TX
boodaddyz said:
Image
Click to expand...

Oh my god a million times no. There is no reason for that product to exist. You cannot run two power-hungry cards off your Mac Pro's internal PSU. You may be pushing it by attempting to use one. The only converters that are legitimately okay to use take two 6-pin PCIe connectors (rated at 75 watts) and turn them into a single 8-pin PCIe connector (rated at 150 watts). Do not split the 6-pin power connectors. Do not bundle the 6-pin power connectors into an 8-pin and subsequently split the 8-pin. Do not adapt the 6-pin power connector to an 8-pin in a way that makes the card think "sure, I can draw 150 watts from this!" Anything you attempt to do with the optical drive power connectors risks damaging your machine, your card, or both.
 
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