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anarchi

macrumors newbie
Original poster
Nov 13, 2020
26
7
I have been running OpenCore and Monterey with an AMD RX5700XT GPU on my Mac Pro 5,1 for the past couple of years and everything has been working fine.

Recently I thought I would give OCLP and Sequoia a try (it took me ages to discover that that wouldn’t work with the 5700XT), so I have replaced the 5700XT with a Vega 64.

Now the problems with the Vega 64 begin. Every so often (and always in some circumstances) I get a sudden black screen and all the fans run at 100%. The only option is to power the Mac Pro off and then on again.

This appears to happen when the GPU is put under load (sitting here writing this, everything is working fine). On Mac OS (either Monterey with OpenCore or Sequoia with OCLP) It happens sometimes with graphics programs processing a photo (e.g. Topaz Photo ai), or occasionally while running a GPU test with Geekbench. Under Windows 10 it happens every time about 2 minutes into a game (Baldur’s Gate 3)

It doesn’t necessarily seem to happen when the GPU is at its most active and it doesn’t appear to have anything to do with temperature (even under load it seems to run at something under 70 celsius and that last time it crashed it was only on 54). It also doesn’t make any difference which position the bios switch is in — it crashes equally with both.

One possibility is that this has something to do with power. However I have the Pixlas mod on my Mac Pro, so power comes straight from the PSU into two eight pin connectors. (Is it still possible that the GPU needs more?)

I have found some others who have had the same black screen and fans problem, but they have all been running windows machines and the discussion usually ends up being about drivers.

If anyone has any ideas in the cmp world I will be very happy to hear them and a solution would be even better.

Thanks to all and my apologies if this has already been discussed (my search skills were not good enough to find it).
 
Your GPU has a defect. I've often seen this behaviour at some Polaris cards, but unfortunately i can't say whats the cause. Maybe undervolting helps.

Common sympton: With load (may vary), sometimes only after loaded drivers, the screen got black and the fan runs on max rmp.
 
Thanks, I have just tried undervolting the GPU in Windows (just using the auto setting in the AMD utility} and it appears to be more stable. I'll try to set it up for the Mac side as well. I think VGTab allows you to do that by creating a kext, but any other suggestions would be welcome.
 
I love the MP5.1 and I love to test all kind GPU's for Apples best Workstation. With Vega I started with the Vega 64 first. Unfortunately the card did run very hot and the single duct fan was loud as hell. At that time I did have the Pixlas already, but the Vega 64 was not a very good card. I sold it off fast to get a Vega 56 which ironically did work a lot better, calmer and produced less heat inside the Mac Pro.
Your description sounds like you have gotten one of those problem cards, maybe an old bitcoin mining card that has a changed GPU firmware an is on its last legs. Check your original source where did you get the card. See if it runs really hot. Is the duct fan somehow covered up because of a longer card in Slot #2? Here are some bit, I would check on the electrical:
#1 In case you have a mint condition card, your description sounds like you could have a small electrical problem.
If you use Pixlas mod for a long time, sometimes one of the contacts could get loose or was not really tightened when you put it in place. When I did install my pixels, I noticed that the small metal clamps inside the yellow covers have a very tight slit. When you put the black wire into the slit, it takes a very very good squeeze with pliers to flatten the cable and to get the flattened metal copper wires into that slit to have a proper and durable contact. If one of those contacts are kind of "loosey-goosey" your Gpu would still work, but your PSU would run on kind of "one leg", which means with GPU#s that are very power hungry, you would experience a black screen, because your max power ceiling is reduced because of one or two loose pixels contacts. So -> check your pixels contacts. Electrically it would also not be bad to reinforce those contacts with some solder.
#2 Another fix would be to use the EVGA PowerLink in combination with Pixlas. Its harder to find these days, but most of the time it doesn't cost very much, around 20 bucks. This bracket equalize the power draw between those 8 cables and makes the power draw less dynamic for the Mac Pro PowerSupply.
#3 And last, check the contact prongs on your GPU socket and your GPU cable. If its a used card, sometimes those sockets have some wear.
Anyways, since you have Pixlas, the other option would be to just sell it off on eBay and go for a Vega VII card.
Thats what I would do. The Vega VII is night and day and runs so much cooler because of the three fan set up.
Its way better than any duct fan. If you can't find it, also a Vega 56 from Power Color with three fans such as the Red Dragon would be recommended and a lot better than the ducted 64, - from a driver and cooling point of view.
Hope this helps.
 
Common sympton: With load (may vary), sometimes only after loaded drivers, the screen got black and the fan runs on max rmp.
I can confirm this with behaviour with an AMD RX480 and the Air Out app (which stresses the gpu to raise the fan speed and overcome the SMC fan issue)

My theory is that it might be caused by drawing excessive power through the PCIe slot. Although it could be a defect in the card, however the card runs fine if I disable the Air out app.
 
I can confirm this with behaviour with an AMD RX480 and the Air Out app (which stresses the gpu to raise the fan speed and overcome the SMC fan issue)

My theory is that it might be caused by drawing excessive power through the PCIe slot. Although it could be a defect in the card, however the card runs fine if I disable the Air out app.
Like I said, that is your fix what you need


PowerLink_EVGA.jpeg
 
Like I said, that is your fix what you need
I have this fitted to a Vega 56 which is in another one of my 5.1s. and occasionally I find my computer in the frozen black screen state, most often when letting it sleep whilst using Lightroom.

My theory is that it might be caused by drawing excessive power through the PCIe slot. Although it could be a defect in the card, however the card runs fine if I disable the Air out app.
The RX480 is known, by design, to draw more power through the PCIe slots than the spec allows, causing back plane burnout in extreme situations!

My hypothesis is a power surge through the PCIe slot is causing the SMC to shutdown the computer and run the fans full blast.

I can recreate the symptom at will using the Air Out app.

One possibility is that this has something to do with power. However I have the Pixlas mod on my Mac Pro, so power comes straight from the PSU into two eight pin connectors. (Is it still possible that the GPU needs more?)

This evidence corroborates my theory about power surge through the PCIe slot.
 
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