Mobo doesnt like GPU?

[Decimus]

Redoing an older build and ran into a problem. I think I might know what's wrong but thought I would ask for more opinions.

MSI K9A Platinum Motherboard
4870 1 Gig GPU
CX430 PSU

Ok so when I hook everything up it will not post but it will provide power to the fans etc. Thought it would be a power supply problem so swap out the CX430 for an antec 650W that is working. However this causes the computer to not even turn on the fans. On the first start the power will flicker and immediately shut down.

Swapped out video cards for a working 460 and same problem. It does however work with a 4830. We did try the 4870 in another build using the CX430 and it does post.

My only thought is that this motherboard can't support the dual 6-pin through the pci-e slot?

 

[Dangman]

You did plug in all the PCI-E power connectors correct?

 

[J Macker]

Yes, we did. With the CX430w psu, we used one molex-> 6-pin adapter.
With the NeoPower 650w, it had two native 6-pin connectors.
I ensured that both power connectors were plugged in to each video card and that all power connectors were plugged into the motherboard during all attempts.

I am stumped about this. I thought initially that the motherboard wasn't providing enough power through the pci-e slot, but then I read on wiki that all pci-e x16 version 1.0 and 1.1 have 10w draw during boot and 25w max.

But I am confused about that; I thought that a standard pci-e x16 slot could provide up to 75w. Is there a setting that should be changed in the bios that might be causing this problem?
It seems like if there's not enough power for the 4870 or gtx 460 for posting, then why does it work with a 4830?

The system worked fine when I plugged in the Radeon 4830 with one 6-pin power connector.
The 4870 and GTX 460 work fine in another system (booted into windows) with the cx-430w psu and the neopower 650w psu.

 

[Dangman]

I am stumped about this. I thought initially that the motherboard wasn't providing enough power through the pci-e slot, but then I read on wiki that all pci-e x16 version 1.0 and 1.1 have 10w draw during boot and 25w max.

But I am confused about that; I thought that a standard pci-e x16 slot could provide up to 75w.

You didn't read the wiki correctly:

PCI Express cards are allowed a maximum power consumption of 25W (×1: 10W for power-up). Low profile cards are limited to 10W (×16 to 25W). PCI Express Graphics (PEG) cards may increase power (from slot) to 75W after configuration (3.3V/3A + 12V/5.5A).[8] Optional connectors add 75W (6-pin) or 150W (8-pin) power for up to 300W total.

Is there a setting that should be changed in the bios that might be causing this problem?

AFAIK, no motherboard has such a feature considering that it's part of the PCI-E specs. It should provide it with the correct power automatically with non-defective motherboard. But I could be wrong about that. Check your manual.

 

[J Macker]

So what's wrong? Why doesn't the 4870 or the gtx 460 work in that motherboard but the 4830 does?

 

[Dangman]

So what's wrong? Why won't the 4870 or the gtx 460 work in that motherboard?

Could be that the mobo's PCI-E slots has become weakened/defective to the point where it can't handle the power draw of those two cards. If you can, try a 4th card to see if that changes anything. I dunno, maybe dust out the PCI-E slots and see what happens.

Also you did try the cards in the secondary PCI-E x16 slot right? Reset CMOS if you haven't already to rule out a wonky BIOs setting.

 

[J Macker]

Yes, we tried the cards in the second pci-e slot and I cleared the bios.

The secondary pci-e x16 slot was previously a virgin. I doubted both slots would be damaged.

There isn't anything else I could think of; that's why I had him make a thread.