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Synchro

macrumors member
Original poster
Nov 11, 2005
61
21
France
A while ago I bought 2 new Samsung monitors to run on my 2008 Mac Pro 3,1 with a GTX770 graphics card. I unplugged the old monitors, plugged in the new ones (using Samsung's supplied HDMI cables, the only ones I've found that will actually run them at their full 144Hz speed). One of the screens came on, the other didn't. I replugged them, and neither came on. I rebooted, no chime, the graphics card fan came on full speed, and there was no video output. I figured I must have killed the graphics card, so I bought a new one (the same model). And that did exactly the same thing!

I then tried using the original 8800GT that was in the Mac Pro when new, and I still have lying around. That didn't run fans, but no video either.

If I remove the graphics card altogether, the machine boots, and I can access it over SSH locally, but of course the logs are filled with errors trying to start the graphics system. I tried one of the cards in a friend's PC, and it also failed to boot (not even a POST) and had the fans run full speed.

Eventually I gave up and bought a 2012 Mac Pro with an RX580, and that works fine with the same monitors. But I'm now left with this half-dead Mac Pro that I'd like to sell, along with 3 not-terrible graphics cards, but it's obviously not going anywhere without working graphics, and I can't tell what's really happened to them.

So I need to diagnose what's gone wrong – is it just the cards, the motherboard, or both? While I could test the apparently dead graphics cards in my new Mac Pro, I'm reluctant to do that for fear of killing it too! It seems bizarre that so much damage cound have been done by simply replugging a monitor! It's tempting to buy a cheap PC just to see if I can diagnose it better on there, since more diagnostic tools on DOS/Windows, firmware twiddling might be possible, and it will have built-in graphics that should always work.

Does anyone have a good idea what might have happened, and how I might diagnose what state things are really in?
 

tsialex

Contributor
Jun 13, 2016
13,463
13,620
First step is to check the RTC BR2032 battery voltage. Low voltage stops the internal RTC counters and this makes your Mac crazy.

Second is to install a know working Apple EFI64 OEM GPU + display combo and do a deep NVRAM reset.
 

Synchro

macrumors member
Original poster
Nov 11, 2005
61
21
France
Do you think the battery is a likely cause given that it boots fine without a graphics card?

FWIW I tried one of the graphics cards in a friend's PC, and it did the same thing – fans come on at full speed, PC doesn't even get as far as starting the BIOS, though I didn't have time to experiment with it any further.
 

tsialex

Contributor
Jun 13, 2016
13,463
13,620
Do you think the battery is a likely cause given that it boots fine without a graphics card?

FWIW I tried one of the graphics cards in a friend's PC, and it did the same thing – fans come on at full speed, PC doesn't even get as far as starting the BIOS, though I didn't have time to experiment with it any further.

For a 10+ years old Mac Pro, the first thing that you check is the battery. People frequently overlook it and then days into the diagnostics find that is the battery. Always start checking the battery voltage, a Mac Pro don't work correctly with the RTC stuck.

Some flashed GPUs don't work with PC UEFI firmwares that expect a GOP UEFI module, you could have tested with one.
 

Synchro

macrumors member
Original poster
Nov 11, 2005
61
21
France
I was surprised to find that I had a Radeon R9 280X lurking in a box I'd forgotten about! I changed the battery (old one was at just over 3 volts), reset NVRAM 5 times, and installed the 280X – and it booted!

Not a complete success because after displaying an Apple logo and a progress bar, it ends up with a blank grey screen. I then tried the two GTX770s again, and both still had the same full-speed fan and no boot progress. I am still very happy about this as it suggests that the Mac Pro is OK ? and it's only the GTX770s that are dead.

Now I'm making a bootable flash drive to wipe my old system and reinstall El Cap on it. Are there any particular issues with the 280X and later macOS versions? I'm wondering whether to bother upgrading it via OpenCore before selling it or to just leave it unmodified.

I'll need some better way of diagnosing these 770s; they are worth a fair bit, but I have a 580X in my 2012 Pro so I don't need them. I may have to go the cheap PC route, which I've been comtemplating anyway.
 

tsialex

Contributor
Jun 13, 2016
13,463
13,620
I was surprised to find that I had a Radeon R9 280X lurking in a box I'd forgotten about! I changed the battery (old one was at just over 3 volts), reset NVRAM 5 times, and installed the 280X – and it booted!

Not a complete success because after displaying an Apple logo and a progress bar, it ends up with a blank grey screen. I then tried the two GTX770s again, and both still had the same full-speed fan and no boot progress. I am still very happy about this as it suggests that the Mac Pro is OK ? and it's only the GTX770s that are dead.

Seems your Mac Pro still works.

Now I'm making a bootable flash drive to wipe my old system and reinstall El Cap on it. Are there any particular issues with the 280X and later macOS versions?

Sierra and newer AMD drivers need SSE4.2, MP3,1 Xeon processor don't support it and won't boot with one unless you install MouSSE.

I'm wondering whether to bother upgrading it via OpenCore before selling it or to just leave it unmodified.
Sell your early-2008 with 10.11.6 fully updated, imagine if you sell it to a person that will be bothering you forever asking for help with OpenCore issues…

I'll need some better way of diagnosing these 770s; they are worth a fair bit, but I have a 580X in my 2012 Pro so I don't need them. I may have to go the cheap PC route, which I've been comtemplating anyway.
You will need to test this with a PC that have CSM/BIOS support. Recent pure UEFI ones won't work for a Mac EFI flashed GPU.
 
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Synchro

macrumors member
Original poster
Nov 11, 2005
61
21
France
Ah, I knew there was something like that. I will keep it vanilla then, thanks for the pointers.
 
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