Mac Pro 5,1 (2010) Black screen on boot (GPU is ok)

[leon771]

I purchased a 5,1 2x2.4GHz least week into which I've transplanted 2x X5680.

When I purchased they machine the previous owner had an Nvidia 460 SE installed as they said the original ATI card died. The owner mentioned that they were having problems with the machine not booting and the gpu fans running full speed. They said they found that the GPU wasn't seated properly and the metal bar restraining the GPU was loose.
In front of me the owner started the machine a few times and it seemed all good. I figured that was the end of that (460 being a short card, perhaps that's why it wasn't seating properly.)

Got the machine home and cleaned out a lot of dust from it with a compressor. Replaced CPUs with X5680s and she seemed ok.
Replaced the 460 SE with an ATI 4870 from my 2009 Mac Pro.

In the past week I've had 2 instances where the machine won't POST.
This evening I installed a HDD into caddy #2. When I turned machine on it wouldn't POST.
In order to get the machine to boot I removed the GPU, reseated it and tried again. No post. SMC reset, same. Pressed RTC reset on backplane and then she booted. It seems like this machine has a finicky backplane where if a little pressure is applied to it, she fails to POST and GPU fan runs full.

I ran AHT and I get a PCIe temp sensor error which apparently is relates to the 5,1 firmware not reading the 4870 temp properly. Extended test gave a 4hdd/11/4000004 sata (4,0) error which i presume is a HDD failing.

All I can think of is that the backplane board is loose or not sitting quite correctly.

Has anyone experienced this or know where I should begin?
I was thinking contact cleaner on PCIe slots as a start.
The backplane to processor board connector looks good.
Could a loose connection between PS and backplane cause a failure to POST and GPU fan to run full blast with a black screen?

Any suggestions welcomed. I hate to think I was ripped off.
When running the machine is fairly stable. Have only has a single KP.

 

[h9826790]

If just that GPU cannot seat properly at slot 1, you can install it in another slot, or even remove it. The computer can boot headless.

If the Mac can't boot headless. Then the failure may be not PCIe or GPU related.

 

[leon771]

I never thought about trying to boot headless.
Do you know if a "loose" graphics card would cause the issue I'm seeing?
Sounds to me that if the cMP can boot headless, then a loose graphics card should be bypassed and the machine should post, unless the presence of a graphics card prevents this.

 

[h9826790]

then a loose graphics card should be bypassed and the machine should post, unless the presence of a graphics card prevents this.

Then it's not a bit loose, but the slot is totally U/S.

A little bit loose may make poor contact on just few contact point, which cause the Mac Pro able to detect there is a card, but unable to initialise it correctly.

 

[leon771]

Then it's not a bit loose, but the slot is totally U/S.

A little bit loose may make poor contact on just few contact point, which cause the Mac Pro able to detect there is a card, but unable to initialise it correctly.

Excuse my ignorance, but u/s is unstable?

If problem persists il try slot 2.
I'm thinking of completing stripping system and cleaning all contacts - ie. PS to backplane, backplane to processor board, PCIe slots.

Thanks for the assistance.

 

[h9826790]

Excuse my ignorance, but u/s is unstable?

If problem persists il try slot 2.
I'm thinking of completing stripping system and cleaning all contacts - ie. PS to backplane, backplane to processor board, PCIe slots.

Thanks for the assistance.

U/S = unserviceable

 

[leon771]

Ran ASD 3S149 EFI and OS tests this evening.
Only error is a Te1S error which refers to PCIe slot temp error (it is reading -124degC).
Seems like it is related to using a 2009 4870 in a 2010 Mac Pro. I don't think there is a sensor on the backplane board, but rather temp is dictated by card.

So hardware wise everything came up good, so its going to ne an intermittent annoying one to solve.

 

[h9826790]

I think it's better to install the card in slot 2 now. If problem gone, then you know most likely your slot 1 is intermittent.

Slot 2 is perfectly fine for GPU, the only down side is that will block the slot 3. But if you don't need that slot, it's actually better cooling in slot2, and no more PCIe fan issue.