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3 4k monitors on mac pro not working

I have 3

Samsung - UD590 Series 28" LED 4K

monitors and i have 2 connected via the mini display port to HDMI and one connected via the HDMI port, apple says this configuration should work but i can't get the 3rd screen to ever fire up, i have tested all three screens and only two of them seem to work at any given time, Use multiple displays with your Mac Pro (Late 2013) - Apple Support, any help would be much appreciated! Thanks!

Mac Pro

Posted on Sep 22, 2015 5:38 PM

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Posted on Sep 22, 2015 6:11 PM

i have 2 connected via the mini display port to HDMI

Those are considered "Legacy" adapters, as is the built-in HDMI port, if you choose to use it. AS the article says, you are limited to TWO legacy displays, not 3.


If you were to use Mini DisplayPort to DisplayPort cables for at least one display, all would work.

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Question marked as Best reply

Sep 22, 2015 6:11 PM in response to kierrereeg

i have 2 connected via the mini display port to HDMI

Those are considered "Legacy" adapters, as is the built-in HDMI port, if you choose to use it. AS the article says, you are limited to TWO legacy displays, not 3.


If you were to use Mini DisplayPort to DisplayPort cables for at least one display, all would work.

Sep 25, 2015 5:50 PM in response to lllaass

He never stated how he fixed it.


For people with a 4K display that has Displayport or MiniDisplayport as an input choice using a DP to HDMI adapter would be a very poor idea.


Most MDP to HDMI adapters are HDMI 1.4 at best. That means 30Hz refresh, at best.


Whereas a display that has DP in could just use a MDP to DP cable and get the full speed possible of 60 HZ.


If you do not understand what this means, go to this site:


http://testufo.com/#test=framerates


It will show you what speed your display is connected at. If you are running at 60Hz, you will also see what 30Hz looks like, the stuttering/skipping one on bottom.


If you only have a 30Hz connection, you won't see the 60Hz UFO.

3 4k monitors on mac pro not working

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