21:9 and 16:9 displays not working together / problem with LG 29UM58-P (2560x1080, 21:9, 29")

Sep 11, 2018
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Hello!

Until now I used Samsung Syncmaster T22B300 (1920x1080, 16:9, 21,5") as my primary display, connected to my computer with HDMI-DisplayPort cable (DisplayPort end going to my GPU. My GPU has one HDMI port and one DisplayPort). I had also at all times Samsung UE40JU6672U Smart TV (3840x2160, 16:9, 40") connected to my PC via HDMI cable. When my friends sometimes came over I would turn on my TV and duplicate the displays so that they could observe whatever I was doing from the couch (in advance - this is the situation that I want to maintain), I didn't touch resolution so the TV would also show 1920x1080 resolution picture, what was still sharp/pleasant enough to the eye. Everything worked fine.

Since 21,5" is really small for today's standards and I game quite a lot on my primary display I decided it was about time to replace my primary display. So today I bought LG 29UM58-P (2560x1080, 21:9, 29") ultrawide monitor. This is where the trouble began. I definitely want to maintain my ability to turn on my 4K TV and duplicate displays (I realise I would then temporarily had to fall back to 1920x1080 resolution on both displays for optimal experience for myself and my audience in the room), but currently the two displays don't get along at all. I was able to get my new primary LG monitor to its native resolution only after unplugging the TV from my computer and restarting it (before that I think the LG ran on 1024x768 after connecting it for the first time). Now, as soon as I plug the TV back into the computer (even if the TV is turned off) my LG monitor reverts to 1024x768. If I then try to force it to 2560x1080 it goes crazy and starts to flicker really fast in the same tone which was prevalent on the display before connecting the TV. Only way to stop it was to unplug the TV and restart computer, switching the LG display itself off-on or disconnecting it from power outlet didn't help.

Relevant PC specs:
Motherboard: MSI B75A-G43
GPU: Nvidia GeForce GTX 970, 1 HDMI, 1 DisplayPort (I use DisplayPort-HDMI cable to connect my primary display)
3,40 gHz Intel Core i7-3770

I want to have my Smart TV connected to my PC at all times without trouble. When I turn on my TV it is not a problem for me to switch resolution with duplicate displays, since the native resolutions (and aspect ratios) don't really fit. So here comes my two bigger questions:

1) Can I make the two displays work together and how? Is it maybe my motherboard's fault? Would replacing my motherboard to one with Z77 chipset help or is it some fundamental problem due to two monitors with way too different aspect ratios or something?
2) Another monitor I considered buying instead of LG was AOC's Q3279VWFD8 (2560x1440, 16:9, 31,5"). If I can't get my LG to work as I want, would replacing it with AOC's model help me?

Thank you in advance!

UPDATE: things that I've tried

I updated LG drivers, it didn't help.

When I tried older games with resolutions 1920x1080 and even 1024x768 I was able to get them to their native aspect ratios on the screen from LG monitor's options (black bars on both sides of the screen), but when I exited the games flickering would start again. this time I discovered that switching the HDMI port on monitor (it has 2 of these) helps and I don't have to restart the computer.

Testing with two setups:
setup1:
extended displays(!)
TV 3840x2160
old monitor 1920x1080
everything works fine

setup2:
extended displays
TV 1920x1080
The new LG won't go to anything over 1024×768

It seems that aspect ratio is really important. This is getting really frustrating...
 
Solution
I found a solution. It turned out that the problem was DisplayPort-HDMI cable. I switched the cables between two displays so that LG got HDMI-HDMI cable and no flickering after exiting the games occurred, however using DisplayPort-HDMI cable on my 4K TV I was able to reproduce the flickering on that screen after exiting the games. I don't think that the cable itself is faulty since it is basically brand new and pins look fine, I think it rather has some compatibility issues with certain monitors (since the original 21,5" display worked fine) and the fact that it is DisplayPort-HDMI cable, which are not quite the same.

My acquaintance, who is an IT guy told me that I could try DVI-D-HDMI cable (GTX 970 also has 1 DVI-D port and 1 DVI-I...
Sep 11, 2018
2
0
20
I found a solution. It turned out that the problem was DisplayPort-HDMI cable. I switched the cables between two displays so that LG got HDMI-HDMI cable and no flickering after exiting the games occurred, however using DisplayPort-HDMI cable on my 4K TV I was able to reproduce the flickering on that screen after exiting the games. I don't think that the cable itself is faulty since it is basically brand new and pins look fine, I think it rather has some compatibility issues with certain monitors (since the original 21,5" display worked fine) and the fact that it is DisplayPort-HDMI cable, which are not quite the same.

My acquaintance, who is an IT guy told me that I could try DVI-D-HDMI cable (GTX 970 also has 1 DVI-D port and 1 DVI-I port, which I overlooked before) since HDMI is basically an upgrade from DVI, being electrically exactly the same (his words) with the only difference that audio transfer has been added to HDMI. And that cable solved all my problems! No flickering after exiting certain games and I can duplicate display on my LG and 4K TV @ 1920x1080 with no troubles. Hell, I can even do extended displays @ 2560x1080 & 3840x2160 (at least on desktop, lol).
 
Solution