Resolved External display problems on 49inch Samsung C49RG90 UltraWide - Garbled (Tearing colours).

AdamSeen

macrumors regular
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Jun 5, 2013
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I've connected a Samsung C49RG90 49-inch to a late 2015 iMac retina, using a Displayport to mini-Display port connector, on macOS Catalina 10.15.2 and it produces tearing colours as shown below.

IMG_1072.jpeg

The display is being detected correctly in system report.

Screenshot 2020-01-12 at 17.45.25.png

The GPU supports displayport 1.2, which should be enough to drive it. I've also tried changing the resolution on the external display to a much lower one, but doesn't help.

Attached it to a PC and works fine (with a different cable), also tried changing ports, but to no avail. I'm thinking it could be the cable? But I thought all DisplayPort cables are the same. Any ideas?
 

AdamSeen

macrumors regular
Original poster
Jun 5, 2013
164
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I managed to find a new DP cable, but no difference. Still garbled.

Tried resetting PR RAM, booting in safe mode and attaching to MacBook Pro 13inch 2013 - nothing. Will get an adapter for my MBP 2018 13 inch see if anything appears on that.
 

AdamSeen

macrumors regular
Original poster
Jun 5, 2013
164
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I was able to fix this problem, with a slight compromise, by using PBP mode on the monitor which uses two cables to separate the monitor into two displays. This will actually make it easier to use productivity apps and full screen. As as far as OSX is concerned, it's two separate displays.
 

AdamSeen

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Jun 5, 2013
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It’s working with the MP 7.1, but not perfectly. I’ve had to get some display adjusting software to reach 120hz. There’s also an unexpected colour difference at the center of the display which can be seen more obviously with certain colours, I suspect it’s the display but will try in windows tomorrow.
 

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SecuritySteve

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Jul 6, 2017
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Does it happen in Windows too? I know someone who is likely to come to me for a monitor recommendation in the near future, and this was one of my initial top candidates until I read this post. Really hoping it's possible to get the full resolution and 120hz on macOS with no issues.
 

AdamSeen

macrumors regular
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Jun 5, 2013
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Tested this earlier today. It doesn’t happen in windows so the weird colour problem is Mac only. It’s far from perfect - you can’t seem to set it to 120hz without an external app and it occasionally has been flickering. I’m not sure if that’s because of the DP to USB adapter that I don’t use on the windows computer.
This being a non IPS panel is also not good for colours in MacOS.
Im likely going to send it back and have a think about next choices.

The other 49inch panels from LG and Dell look good, both using the same IPS panel, but not 120hz. Unfortunately the panel I really want doesn’t exist yet. 120hz, IPS, retina, ultra wide
 

SecuritySteve

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Jul 6, 2017
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California
I feel you here. High refresh rate and high resolution often don't jive due to the bandwidth multiplier. Last I checked 120hz 4k resolution pushed the limits of Thunderbolt 3. Scale that down to an appropriate "retina" size at 21.5 inches and we're just not satisfied with the screen real-estate.

To get to 120hz on say a 43inch 8k monitor or TV, you would need to have a total bandwidth of 119.44 Gbps. Now if you just doubled the resolution of your Samsung monitor ... 10240x2880@120Hz = 106.17 Gbps

Thunderbolt 3 allows for connection speeds up to 40Gbps. Perhaps Thunderbolt 5 will have enough bandwidth for the monitor you want.