You will have to test this but maybe a 4K HDMI Splitter is the cheap fix here as well, you are a consultant/builder and more so I'm going to stop here and not explain why I think this could cure it.
https://www.google.ca/search?client=opera&q=4k+hdmi+splitter
I have a very vexing issue involving multiple displays on a customer's computer system, and I'm looking for a solution. This is probably a common situation for gamers, but I'm not one and neither is my customer, so I'd appreciate any insight anyone has.
He's a music teacher. He does a lot of video work. He has a 4K TV -- a Sony -- and when it was time to get a new computer, he wanted 4K on that as well -- and he also wanted to be able to output the computer's video to the HDMI input on the TV, also in 4K. I set him up with an HP Envy refurb, core i7, with an XFX RX-460P4DDGR video card (Radeon RX-460) and an AOC U2879VF monitor. So far, so good. The AOC monitor is connected to the card with a DisplayPort cable, and the TV is connected with a 4K-capable HDMI cable.
Of course, when you set the resolution on a 28" 4K monitor to the native recommended size, we old folks can't read anything that's on the screen.
With some tweaking, I managed to find both a resolution and a zoom level that worked quite well for both the monitor and the TV.
(I should mention that the TV's inputs are controlled by the Sony home theater receiver to which it's connected. (Yes, it's 4K capable.) So the HDMI cable from the computer goes to an input on the receiver and thence out to the TV.) In Windows 10, I've got the two displays both set as "1 | 2" -- since I don't want to confuse the customer with an extended desktop.
The problem is this: when the receiver is turned on -- even if its input is set to the cable box or blu-ray inputs and NOT to the computer input -- the video on the AOC monitor goes through a crazy dance of changes in resolution, size, and position -- two or three iterations that take a total of up to almost a minute sometimes. The same thing happens when you turn the receiver back off. And sometimes it would actually stay in an unusable display format and not fix itself till the computer was restarted. I played with all the settings again and I got it to stop ending up in an unusable state, at least, but the odd dance continues. I've tried using the other DisplayPort on the XFX card with an HDMI adapter -- no change. I even tried running the TV's HDMI cable through the computer's onboard HDMI connector -- even though it of course is not 4K and therefore wouldn't be acceptable to the customer -- just to see if it would at least make a difference. It does not. I haven't yet tried the extended desktop on Windows 10, but I don't know if that would help at all.
I'm now at the point where -- if that doesn't work -- I have to start trying to change-out hardware components. And I'd rather not experiment. My first guess would be to use two separate video cards -- but of course the HP has only one slot and I'd have to replace the computer as well. That's not out of the question, but it's definitely a last resort and I'd only do it if I knew in advance that it'd work.
I'm sure, as I said, that this is a situation gamers run into all the time -- but I don't.
So any insight would be appreciated. Thanks, and sorry for the long explanation...

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