RX580 with Three Monitors Issue

gadgetfreak98

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Feb 6, 2009
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Hi all. I have a Radeon Sapphire Pulse RX580 (the Apple "recommended" one) hooked up to my Mac Pro 4,1->5,1 running Mojave 10.14.3.

I recently decided to get a 4K monitor (LG 27UK850) to swap in for an old Dell 24" 1080 monitor. I continue to use my 30" Apple Cinema Display.

With the 30" ACD via DVI and the LG via Displayport, all was fine.

Then I decided I would keep my Dell and use it in portrait mode for Word docs, etc. I tried to hook it up with a DVI-DVI cable with a DVI-HDMI adapter on one end to an HDMI port on the card. I know the adapter is fine, having used it as part of the prior setup with just the ACD and Dell. However, no image shows up on the Dell in this setup. I tried rotating to landscape, just in case, but no luck.

Interestingly, I can see in the displays arrangement systems utilities control panel all three and can drag around the placement. But no image...

Any suggestions? Are three monitors in my setup just not possible? Thought this card could drive a whole bunch of screens (e.g., at least 3 with only one 4K).

Thanks!
 

gadgetfreak98

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bsbeamer

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What resolutions are all monitors using?
Are you maxing out available/drivable resolution with the 4K and extra two?
Did you try reducing resolution of all monitors?
Dell monitor have a menu setting for changing the version of incoming signal?
 

mode11

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To make things simpler, try disconnecting all monitors except for the Dell. I would imagine an RX580 could drive 3x 4K monitors simultaneous (obviously it wouldn't have the performance to run games like this).

I've had issues with long HDMI cables before, but that was probably more an HCDP (copy protection) thing. The control signal lines can be intolerant of interference, and if there's any handshaking issue the screen just goes blank. There was plenty of video bandwidth (1080p is not high resolution) and never any speckles in the picture when it was working.

All HDMI - DVI adapters will be passive, since the video signals are the same. HDMI just adds audio.

What resolution does it say in System Preferences? Set it to Scaled (not Default for Display), then make sure 1920x1080 is selected. Make sure the Refresh Rate is 60Hz, if selectable.
 
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gadgetfreak98

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Feb 6, 2009
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I will try as you suggest when I'm back in front of the computer this evening.

I'm running the LG @ 1440 lines, but that is scaled I would think? e.g., look like 1440 lines of resolution, but sharpened text and images...

The ACD is at native resolution of 2560 x 1600.
 

mode11

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Definitely scaled. 4K is 3480 x 2160. Sounds like you're running it at 2560 x 1440, the typical res. of a decent 27" monitor.
 

gadgetfreak98

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Feb 6, 2009
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Yes, I am not running at the full resolution of 2160 lines, as I am preferencing sharpness over screen real estate and trying to get the two screens to effectively have size consistency as I drag windows from one to the other, etc.

But I'll see if I reduce it to 1080 vs. 1440, if that magically makes the Dell reappear. I'll also just run with the Dell as you suggest, assuming issues still persist evening at a 1080 scaling for the 4K LG.
 

bsbeamer

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I cannot find verified or published maximum resolution specs for the RX580.

The NVIDIA GTX 1080 is rated for a maximum display of 7680x4320@60Hz via two DP connections. That's basically two 3840x2160 monitors. (Does not necessarily mean macOS can work with that cleanly.)

Some fuzzy math... Would assume the RX580 is similar (or maybe even slightly less). Based on this assumption, if you're driving 3840x2160 on one monitor and 2560x1600 on another (30" ACD was rated at that if I recall), that would leave you around 1280x560 (less than 720HD) resolution for the third monitor. You simply might be maxing out the GPU's resolution.

Try knocking down resolutions across board and see what your result is.
 

h9826790

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I cannot find verified or published maximum resolution specs for the RX580.

The NVIDIA GTX 1080 is rated for a maximum display of 7680x4320@60Hz via two DP connections. That's basically two 3840x2160 monitors. (Does not necessarily mean macOS can work with that cleanly.)

Some fuzzy math... Would assume the RX580 is similar (or maybe even slightly less). Based on this assumption, if you're driving 3840x2160 on one monitor and 2560x1600 on another (30" ACD was rated at that if I recall), that would leave you around 1280x560 (less than 720HD) resolution for the third monitor. You simply might be maxing out the GPU's resolution.

Try knocking down resolutions across board and see what your result is.
Asus said their RX580's max resolution is 7680x4320.

https://www.asus.com/us/Graphics-Cards/ROG-STRIX-RX580-O8G-GAMING/specifications/

Same max resolution from Gigabyte as well.

https://www.gigabyte.com/Graphics-Card/GV-RX580GAMING-8GD-rev-10-11-12#sp
 
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mode11

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7680x4320 is actually 4x 4K monitors, in a 2x2 grid...

You should always run the monitor itself at its native resolution, for maximum sharpness. This will also let you look at photos, videos etc. with maximum detail. Then adjust the "Scaled" setting to get UI items such as menus, icons etc. to a size that you're comfortable with / matches your other screens.

The 30"/1600p ACD is 100dpi and 24"/1080p Dell is 92dpi, so you'll have to find a compromise that suits both in any case.

What other inputs does the 1080p Dell have? If it has HDMI, just use that natively.
 
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bsbeamer

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The specs for the GPU are PCIe 3.0, which the Mac Pro is not. Can 8K really be driven from PCIe 2.0 via macOS in MP5,1 at 60Hz?

If the OP has any updates on resolution changes, please let us know.
 

gadgetfreak98

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Feb 6, 2009
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Hi all. So I arrived home last night, ready to mess around with settings per the discussion above. However, when my Apple Watch unlocked my computer, lo and behold, the Dell decided to show an image. Now it was not properly rotated no properly arranged, but after fiddling with the Displays control panel, it was set up as I had hoped. In the process of changing the screen's rotation, it oddly did kick the LG 4K down to a lower resolution, but I was able to put it back to 1440 without the Dell losing its image.

So I cannot say what changed. Just seemed that somehow, in the passing hours of the work day, things kind of fell into place. I will see if it persists. On a related note, it is hard to put the Dell back into the rotation after living only with the ACD 30" which always had a better than typical quality (and dot pitch, I think?) and the new LG. It's also a massive space consumer on my desk... But I'm going to live with it a while and see if it (1) continues to function properly and (2) adds enough value to my workflow to put up with the antiquated quality and space consumption.

Also, mode11 mentioned switching to native HDMI on the monitor, if it had it. It does not. This thing is old. DVI, VGA, composite and S-video are what is on offer. I dare say that I've gotten my money's worth out of this thing...
[doublepost=1548857320][/doublepost]Furthermore, in reading mode11's post, maybe I'm missing... But how do you do both native resolution and scaling. I was wondering about whether I was actually getting my full 4k benefit as things didn't seem quite as sharp as I anticipated. And I suspect that's exactly what I'm doing wrong. Thanks for the tip!
 

h9826790

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The specs for the GPU are PCIe 3.0, which the Mac Pro is not. Can 8K really be driven from PCIe 2.0 via macOS in MP5,1 at 60Hz?

If the OP has any updates on resolution changes, please let us know.
AFAIK, PCIe 2.0 or 3.0 doesn't really matter (especially if the slot is a x16 slot)
 

bsbeamer

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AFAIK, PCIe 2.0 or 3.0 doesn't really matter (especially if the slot is a x16 slot)
Typically would assume the same, but I'm not 100% positive on the Apple driver. There really is no documentation on what it supports (or does not support) when an RX580 is installed in MP5,1. I've seen loose specs for RX580 via TB3 in eGPU, but that's an entirely different situation from MP5,1.
[doublepost=1548860382][/doublepost]@gadgetfreak98 I have noticed similar behavior with HDMI devices connected to GTX 1080 FE in High Sierra at times when used in multiple monitor configurations. Often "triggering" resolution changes sends a refresh signal to the device(s) and images appear. For some reason they do not load immediately at boot, or they display no image... but macOS recognizes the monitor in System Preferences > Displays. Installing SwitchResX was able to fix this (for the most part), but did require disabling SIP. Regardless, it seems like DP/mDP simply works better with macOS vs HDMI and use whenever possible.
 

mode11

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The specs for the GPU are PCIe 3.0, which the Mac Pro is not. Can 8K really be driven from PCIe 2.0 via macOS in MP5,1 at 60Hz
Yes, that will have no bearing on it. It’s more to do with amount of VRAM and the spec of the DisplayPorts / HDMIs.
[doublepost=1548867162][/doublepost]
But how do you do both native resolution and scaling
Reread my post. The scaling refers to the setting in Sys Preferences > Displays that controls Retina scaling. It can either be Native (minuscule icons etc), 2x scaled (I.e. using 4 pixels for every UI pixel, for sharp rendering), or some compromise in between.
 

gadgetfreak98

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Original poster
Feb 6, 2009
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Typically would assume the same, but I'm not 100% positive on the Apple driver. There really is no documentation on what it supports (or does not support) when an RX580 is installed in MP5,1. I've seen loose specs for RX580 via TB3 in eGPU, but that's an entirely different situation from MP5,1.
[doublepost=1548860382][/doublepost]@gadgetfreak98 I have noticed similar behavior with HDMI devices connected to GTX 1080 FE in High Sierra at times when used in multiple monitor configurations. Often "triggering" resolution changes sends a refresh signal to the device(s) and images appear. For some reason they do not load immediately at boot, or they display no image... but macOS recognizes the monitor in System Preferences > Displays. Installing SwitchResX was able to fix this (for the most part), but did require disabling SIP. Regardless, it seems like DP/mDP simply works better with macOS vs HDMI and use whenever possible.

Yes, it feels like it makes sense, if I'm going to stick with the 3 monitor setup, to install one of the resolution utilities. Used SwitchResX lifetimes ago, but can consider going back. Do they all generally require SIP disabling?
 

bsbeamer

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Sep 19, 2012
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Yes, it feels like it makes sense, if I'm going to stick with the 3 monitor setup, to install one of the resolution utilities. Used SwitchResX lifetimes ago, but can consider going back. Do they all generally require SIP disabling?
Believe so. SwitchResX can have SIP re-enabled once profiles are established, however it needs to be disabled again after every update in order to access those profiles appropriately. Personally find it easier to just run two monitors with more standard resolutions at this point on MP5,1 if at all possible. Single monitors for HDPI work ok, but multiple seem to cause display issues like this.
 

mode11

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Jul 14, 2015
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Regardless, it seems like DP/mDP simply works better with macOS vs HDMI and use whenever possible.
The thing with HDMI is that it's a consumer electronics standard, so computers tend to assume that you will be running TV-style resolutions and refresh rates. E.g. it may be that the computer outputs on HDMI at 59.94Hz, whereas the monitor wants 60Hz (though I'd expect most monitors to adjust to such a small difference). DisplayPort is only used by computer monitors, so likely supports them better.

It sounds like the monitor is working now, but if it proves flaky, the OP could consider using a DP > VGA cable. They're very cheap, won't noticeably affect image quality, and might avoid the issues seen here.