aacemyan

macrumors member
Original poster
Nov 20, 2017
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Recently purchased a Sapphire Vega 56 Pulse for my 2010 Mac Pro running on Mohave 10.14.6. The card runs fine until i try running a benchmark such as unigine heaven. Half way through the benchmark the Mac shut down completely. I remember reading that for a Vega 56 card, the Pixlas power supply mod isn't necessary. Is this issue power supply related or something else possibly?
 

goMac

Contributor
Apr 15, 2004
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I remember reading that for a Vega 56 card, the Pixlas power supply mod isn't necessary.

That's not true. It totally is.

The Vega 56 draws power in an unbalanced way. Even though the Mac Pro technically meets the total power requirements. it still doesn't provide enough power to each individual booster.

Another option is turning the Vega 56 to low power mode. There should be a switch somewhere on the card. That might bring the card into the right range, but will leave performance on the table.
 
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krakman

macrumors 6502
Dec 3, 2009
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I have read this is a common problem. The solution is simple....don't run benchmark programs!

I have a vega 56 in my 4.1>5.1 12 core 3.46 and it works fine, no hard shutdown ever.

I use an evga powerlink and set the bios switch on the gpu to economy mode.

My main use is FCPX i have the Hardware avcell enabled and it works perfectly.
 
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zedex

macrumors regular
Oct 21, 2018
230
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Perth, WA
I have this same problem. Sapphire RX VEGA 56 shuts my cMP 5,1 down well before I push it with something like benchmarking software. It lasts 1 minute in some cases and 15-20 in others but it ALWAYS causes a hard shutdown.

Where is the low power mode bios switch? Are you talking about the dual-bios dip-switch? What makes you think one mode is low power? and which switch position is it?
I have an EVGA powerlink and it hasn't helped at all.
Nor has it helped to power it using my NETSTOR external PSU.

Makes me think the 'unbalanced power draw' argument is correct and that AMD should be embarrassed that a world-class GPU has been undermined by shoddy electrical engineering :/
 
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h9826790

macrumors P6
Apr 3, 2014
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Hong Kong
I have this same problem. Sapphire RX VEGA 56 shuts my cMP 5,1 down well before I push it with something like benchmarking software. It lasts 1 minute in some cases and 15-20 in others but it ALWAYS causes a hard shutdown.

Where is the low power mode bios switch? Are you talking about the dual-bios dip-switch? What makes you think one mode is low power? and which switch position is it?
I have an EVGA powerlink and it hasn't helped at all.
Nor has it helped to power it using my NETSTOR external PSU.

Makes me think the 'unbalanced power draw' argument is correct and that AMD should be embarrassed that a world-class GPU has been undermined by shoddy electrical engineering :/

If external PSU doesn't help. And the hard shutdown not straightly related to GPU demand. Then something is very wrong.

Did you try that card on another computer?
 
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tsialex

macrumors G3
Jun 13, 2016
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I have this same problem. Sapphire RX VEGA 56 shuts my cMP 5,1 down well before I push it with something like benchmarking software. It lasts 1 minute in some cases and 15-20 in others but it ALWAYS causes a hard shutdown.

Where is the low power mode bios switch? Are you talking about the dual-bios dip-switch? What makes you think one mode is low power? and which switch position is it?
I have an EVGA powerlink and it hasn't helped at all.
Nor has it helped to power it using my NETSTOR external PSU.

Makes me think the 'unbalanced power draw' argument is correct and that AMD should be embarrassed that a world-class GPU has been undermined by shoddy electrical engineering :/
The problem is more complex than appears at first glance. Apple designed MP4,1 around eleven years ago in a world that the power hungrier workstation GPU used around 150W in a very balanced way. Now GPUs use multiples of this and in a very unbalanced way, some using very little PCIe slot power while others use a lot from it. MP4,1/MP5,1 were never designed to have GPUs so power hungry and with so diverse ways to be powered.

AMD got burned with the initial release of Polaris GPUs, they used more power from the PCIe slot than they should and a lot of PC motherboards that were designed without tolerance for overspec power consumption burned the PCIe slots. After that debacle, GPU power plane design changed and hardware engineers in general tried to use less from the PCIe slot and more from the PCIe power connectors, but it's not a rule and we see various degrees of PCIe power balance.

One example that causes frequent problem here, some Dell gaming and workstation GPUs were designed to use more power from the PCIe slot, since the Dell PCs/workstations motherboards were designed to power the GPU mostly from the PCIe slot. These GPUs don't work well with MP5,1, there are dozens of posts about this problem.

Anyway, the problem is that MP4,1 was designed for a different world. We have to thank Apple for how tolerant and resilient the power design proved to be, but eleven years later it shows it's age.

You should check if your NETSTOR external PSU can cope with the VEGA 56, maybe this GPU is defective. Did you tried it with a PC that is capable to power it?
 
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zedex

macrumors regular
Oct 21, 2018
230
91
Perth, WA
Unfortunately, I can't try it on another computer. It may be the Mac Pro internal PSU - other cards make it click off as well (the VEGA is just the biggest culprit). Your bridging solution looks nice @h9826790 - is there actually a 'low power mode' switch? :)
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Thank you @tsialex - That's a very revealing (and comprehensive) rundown. I think I might have issues with the PCIe slot ('burned PCIe slots'). It works better in slot 1 than slot 4 (even though electrically it shouldn't be a problem).

I do want to try powering it with the NETSTOR exclusively but I don't have the right cable combinations at the moment. I'll give you an update when I get the chance to test it. Thanks again.
 
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h9826790

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Apr 3, 2014
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krakman

macrumors 6502
Dec 3, 2009
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Are you talking about the dual-bios dip-switch? What makes you think one mode is low power? and which switch position is it?

i think its switch towards the fan, economy bios, read the instructions to confirm.

are you on 10.13.6????

the mac drivers pull too much power over the 6 pins and nothing from the pic slot. you need to be at least on mojave 10.14.5 which takes more power from the PCI-E slot and less from the mini 6 pins

please update you signature with the correct spec of your machine
 
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aacemyan

macrumors member
Original poster
Nov 20, 2017
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Ok I’ve solved my problem thanks for the suggestions on the bios switch. When I moved the bios dipswitch closer to the back faceplate, it fixed the shutdown problem for my Sapphire Vega 56. Running benchmarks no longer kills the computer.

what is the performance impact of running the card this way? Ideally I don’t want to do the power supply mod but if performance impact is big I may have to do the mod.
 
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h9826790

macrumors P6
Apr 3, 2014
15,233
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Hong Kong
Ok I’ve solved my problem thanks for the suggestions on the bios switch. When I moved the bios dipswitch closer to the back faceplate, it fixed the shutdown problem for my Sapphire Vega 56. Running benchmarks no longer kills the computer.

what is the performance impact of running the card this way? Ideally I don’t want to do the power supply mod but if performance impact is big I may have to do the mod.

Should be very insignificant in general. You should see few % difference in benchmarks. However, for real world usage, unless your workflow is super GPU limiting, most likely you can't tell the difference.

Anyway, power mod shouldn't be required. However, still highly suggest you balance the power draw. Keep over drawing from one of the mini 6pin isn't a good idea.
 
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krakman

macrumors 6502
Dec 3, 2009
286
300
Ok I’ve solved my problem thanks for the suggestions on the bios switch. When I moved the bios dipswitch closer to the back faceplate, it fixed the shutdown problem for my Sapphire Vega 56. Running benchmarks no longer kills the computer.

what is the performance impact of running the card this way? Ideally I don’t want to do the power supply mod but if performance impact is big I may have to do the mod.


toms hardware review:

Using the secondary BIOS with a power limit reduced by 25% gets us 159.4W and 32.7 FPS. Compared to the stock settings, just 71.6% of the power consumption serves up 89% of the gaming performance.


https://www.tomshardware.com/uk/reviews/radeon-rx-vega-56,5202-22.html
 
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K Funk

macrumors newbie
Nov 26, 2019
10
3
I purchased a MVC Vega 56 with boot screen but I'm having the same issue even in low-power mode it still shuts the machine down under load. I've confirmed a stock Vega 56 doesn't have this issue even when only powered by the internal booster ports. Of course I use a EVGA Powerlink as well but no matter how I try the one I bought from MVC still shuts the machine down.

I think the problem, at least with the MVC card, is that it seems to be running a Vega 64 bios making it draw 220 watts+ whereas a stock Vega 56 only draws 160 watts. I've confirmed it running 1630/945 where it should be 1590/800 GPU/MEM. Of course MVC has ignored repeated emails for help.

I still maintain a stock Vega 56 should run just fine on internal power with a EVGA Powerlink, I can't get mine to shutdown in that configuration but with the MVC Vega 56 installed the machine shuts down almost immediately. No bueno.
 
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