If you ran the terminal command it could actually coincide with a reboot (to install cards) perhaps? I think it was much better after a reboot than before for me. 
The 660 errors have returned. Because of course they have. Siiiiiiiiiiiiiiiiiiigh. Guess I’m back to the 710 until Nvidia drivers finally come out or I can afford to get a 680.
Finally located a GTX 680 for $120. It’s being shipped. @jaysee can you tell me, do I absolutely need both of the plugs? I only have the one for the GTX 660, but the 680 has two six hole plugs. I’ll need to order another one (and the first one was a pain to plug in as it was) if so.
Yup you do. Get a 6pin → 6pin (or 6pin → 8pin cable) on eBay if it’s a 8-pin second plug. Is it a Mac card already or are you needing to flash?
I need to flash. Dosdude1 (who has kept us going with Sierra/High Sierra/Mojave on the 3,1) has a process for flashing this exact card.
I think it is 6 pin 6 pin:
I already have one… 6 pin to… mini-6 pin for the 660? I think:
So I need another one?
Yep, you will 2 of them. Perfect. They should be like $5 on Amazon.
I also outlined the flash process here on AppleTalk, btw. 
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It didn’t work! Now the 680 is borked. I made a back up, but how do I actually manage to fix it if I can’t even see anything?! Help @jaysee! Did I just blow a bunch of money?
Looking back at Sugarway, apparently I need to put it into a PCI slot to reflash it or something? Or a PC?
I have tried every combination of PCI slot and other card. And I get no signal from either card.
Could it be because I ONLY have Nvidia cards and I need an AMD/ATI card?
Doing still more research it appears that the only way out of this is to find and use a PC and set the BIOS to specifically choose one display adaptor over the other? Since there is no BIOS on a Mac Pro, this is impossible to set, and no matter what you do, it will always try (and fail) to use the borked GTX 680? I don’t understand why though. Is it because it’s the best card in the system even compared the 710 or the 950 which are newer cards?
I’ll tell you one thing, I’ve learned my lesson, if I get this back to the original ROM, I’m leaving it be. I don’t need a boot screen that badly. I only planned to do this because it sounded so easy.
Hey @kionon. Sorry have been away for a few days. A couple of questions…
- Did you have both power cables connected?
- Did you confirm the card worked when you first booted the machine with just it in it (just no boot screen support)?
- I assume you were doing the flashing from Windows. Did you download the exact versions of the software from my post?
- Do you have another Mac compatible card (i.e. GT210 or the like that doesn’t need a power cable? You can only run one card that needs two GPU power cables at a time from the Mac Pro.
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Yes.
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Yes, I spent two days testing it.
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Yes, I did. However, your versions were NOT the same as dosdude1’s, and now I wonder if I should have used his versions and not yours.
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Not EFI boot screen compatible. I have the GT 710 which works just fine, minus the boot screens.
Which slots did you have the cards in? Have you tried putting the GT710 in slot 1 (bottom) and then the GTX680 in one of 2-4? Will it boot with display then connected to the GT710?
I have tried literally every single combination of PCI slots for the GTX 680 and the GT 710. It boots just fine with ONLY the GT 710. It will not boot with any combination of any two cards where one card is the GTX 680, even if it is plugged in with both connectors, and even if the only display cord used is connected to the GT 710 or other card that is not the GTX 680. But I am completely willing to try it again.
Have you tried setting the boot volume to Bootcamp in sysprefs, then shutting down and putting in the GT710 with display cables and GTX680 without, then powering on again and waiting to see if windows shows anything on the display?
It’s been a couple of days now, but yes, I believe I did try this. I am willing to try again.
Edit: Doing this right now. GT 710 in slot 1, GTX 680 (with power cords) in slot 2. DVI cable connected to GT 710. I’ve got nothing. But the computer is staying on and running. Windows drive is humming along (it’s a mechanical drive). Not getting any beeping, it’s not shutting down, but no display at all.
Any access to a PC? Your note about being able to access one to set the boot priority to the internal graphics or second PCIe would likely allow you to fix the issue…
Yes, I have access to a HP Z400 workstation at the office I can use tomorrow. I have limited experience with PC BIOS options though, so I’m wondering if I am assuming a lot even thinking it has such a feature…
I’m going to guess the BIOS screen will use any available video card? Maybe? I hope? I mean I still need to see the BIOS screen somehow to use the BIOS. I don’t see anything on the Mac Side, not even a flash. The monitor stays off.
Does the workstation have a integrated graphics graphics? Ideally if it has internal GPU, you just boot into BIOS and set it to prioritise internal graphics (not PCIe, not ‘auto’). If it doesn’t, you may need to choose a specific PCIe slot… not sure.
It does not:
