Dual power supply for Geforce 7800 GTX

[cyberjunkie]

My question is about the modifications i am making to a late 2005 Powermac G5.
My first problem is about powering a reflashed Geforce 7800 GTX video card.
I just got the card at home, and i am going to fit it on a PC, and flash a Mac firmware onto it.
If everything goes the right way i should end up with a working video card, but i must supply the extra power needed by the card via a 6-pins power cable.
Unfortunately i just purchased the needed cable from a chinese Ebay shop: very cheap, but very likely to get here after a month or so!
In the meantime i would like to test the card, to see if the new firmware is correctly working with my Powermac. To do that i have two choice:
1) split one or two power cables, either the molex for the dvd drive or also one of the sata that power the two HDDs (i have at home a sata to 2 molex splitter), and connect one of those adapters that have two molex in, and one 6-pins out.
2) the second choice would be to place an ATX power supply on top of the case, short the green cable with the ground, and route the 6-pins PCI-E power cable inside the case, removing the I/O shields of an unused slot.

Any problem with the second option?
The only thing that comes to my mind is that the internal and the external power supplies don't have the ground in common, but i don't think that it's a problem.
But before i would like to get a confirmation.

I am doing another two mods, if somebody has still some interest on those old PPC computers, i'll share my little experiments.

have fun

CJ

[aquamac]

cyberjunkie, does your card have a 128 kb rom chip on it. If it does not, you could trash your card. Check with NVFlash. You can pick up one of those connectors for about 99pence from most computer shops.

[ginz111]

Keep us posted on your updates. I am one of the few Motorola junkies that still hangs here.

[cyberjunkie]

Apr 23, 2010 19:02:19 GMT aquamac said:

cyberjunkie, does your card have a 128 kb rom chip on it. If it does not, you could trash your card. Check with NVFlash. You can pick up one of those connectors for about 99pence from most computer shops.

Do you mean those adapters with two molex on one side, and a 6-pin plug on the other?
All those adapters are very short, i can't reach the card!
The two only places where you can get the power are the molex that connects to the dvd, and the two sata power connectors that go to the disks.
The only way to reach the card would be to custom make a connector, that can be attached to two splitters.
I don't know how the power supply of the Powermac 2.0Ghz dual core is made:
if all the cables that go to HDDs and DVD draw the current from the same line, or not.
If the power line is one, there should be no need to draw the power from two different plugs.
Anyway, it's weekend, and i don't have at home the needed stuff to make a custom cable!
So i am asking if it's safe or not to use a second power supply to power the video card.
I have used a second power supply many times, even with the Powermac, for example to try a few SAS disks i have connected externally, but the video card is different, it draws the power from the PCI-E slots AND from the 6-pin cable . I am absolutely ignorant about electric circuits, so i have no clue about the viability of that solution.


I don't know about the size of the ROM on my card.
I just got it for very cheap, the brand should be XFX, but the cooling device is not original, so i can't confirm it. I only know that it's a Geforce 7800 GTX with 512MB of VRAM. The forum member who gently sent me the rom image told me that all cards are pretty much the same.
I have always found that flashing apps would refuse to work if the ROM is not of the right size/model.
Should i take any special care when flashing the card?

if anybody has the answers, i'd be very grateful
I have time to experiment during the weekend, but i don't want to do anything wrong just to save a few days! :-)

have fun

CJ