Early 2008 Mac Pro 3,1 Mystery Logic Board/GPU Issue

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Early 2008 Mac Pro 3,1 Mystery Logic Board/GPU Issue

I recently received an Early 2008 Mac Pro 3,1 for free because the owner couldn't figure out what was wrong with it. It would boot up with the startup chime, but never output any video, and kept rebooting and replaying the startup chime. Using the diagnostic LEDs on the logic board, I was able to see that the Power Good LED (LED 7) and the EFI LED (LED 9) were both on, but the GPU LED (LED 8) never lit up. After trying all the PCI slots and confirming that the graphics card worked in another Mac Pro, I confirmed it wasn't the graphics card. I then tried a different power supply and different power supply cables, different RAM, different RAM boards, but still nothing. (Note: I also went through all the usual stuff: Power Cycling, PRAM, SMC Reset)

I then ordered a replacement logic board (used from eBay) and spent the weekend swapping out the logic board. After the swap, the Mac Pro STILL won't output video, and now the EFI LED (LED 9) won't even light up. Tried resetting the EFI Firmware via a CD, and still nothing. Does anyone have any idea as to what the issue could be? I'm 95% certain I plugged everything back in correctly on the board, but I don't know what else to do other than tear it apart again to confirm everything is plugged in. The only other thing I can think of is that the second logic board I received was also bad.

Please help!!!

Posted on Mar 29, 2015 8:03 AM

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Answer 1

Apr 3, 2015 10:36 PM in response to shadowjak

Try a new PSU. (Power Supply Unit).

For what I've read on your post, it seems to be the PSU.

Try getting a new PSU and connecting it with the first logic board you had when you got the Mac.

I cannot guarantee anything but thats what I think the problem is.

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Answer 2

Apr 4, 2015 7:33 AM in response to shadowjak

Your problem sounds like a graphics card problem to me.

confirming that the graphics card worked in another Mac Pro,

Was this also a Mac Pro 2008 model? was it running the same Mac OS X version as you are testing? what version?

what graphics card are you trying to use? Genuine Apple or flashed PC or unflashed PC? what Mac OS X version?

That second board sounds Bad to me if it won't say EFI-OK.

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Answer 3

shadowjak Author

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Apr 4, 2015 8:50 AM in response to Grant Bennet-Alder

Yep, Grant nailed it. Turns out the other Mac Pro I checked the graphics cards with was a 2007 model 1.1. Once I got a graphics card that was compatible with the 2008 Model 3.1, everything is working as expected.

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