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P2720DC, S2721Q, daisy chain, flicker
hello everyone.
Previously I had a P2720DC & a P2720D. Everything worked perfectly.
The DC was connected to my Latitude 5490 via USB Type-C. The P2720DC was connected to the P2720D via DisplayPort out.
I recently swapped out the P2720D with a S2721Q and am having issues with the S2721Q flickering when connected the same way in Windows 10.
Both are set to 1440P with 60Hz
The S2721Q doesn't flicker on either of the HDMI inputs, only when connected to the P2720DC via DisplayPort out.
Anyone have any thoughts on what could be causing this? Shouldn't these 2 displays work together seamlessly?
Appreciate your inputs.
jphughan
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January 15th, 2021 13:00
@nikisixx21 Go to Windows Display Settings, click "Advanced display settings", and select the S2721Q in the dropdown at the top. Is 1440p showing as both the desktop resolution and active signal resolution, or does the desktop resolution show as 1440p while the active signal resolution show as 4K? If it's the latter, then your system is rendering to both displays using 1440p, but it's trying to send a 4K signal to the display, and since there isn't really enough bandwidth for that daisy chain setup if both displays are at 60 Hz, that may be the cause of the flicker. If so, try setting resolutions and refresh rates using the Intel Graphics Control Panel / Command Center instead, which might force the active signal resolution to change as well.
But incidentally, why are you running a 4K display at QHD resolution? That will typically look worse than just having a QHD display in the first place, because a QHD image does not map cleanly onto a 4K physical pixel grid.
jphughan
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14K Posts
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January 15th, 2021 14:00
@nikisixx21 Nice! Glad I was able to help and that you found a solution you're happy with. 4K 30 Hz and QHD 60 Hz require roughly the same amount of bandwidth, so as long as the 30 Hz refresh rate doesn't bother you in the form of laggy motion, that would give you superior image quality. Enjoy your new setup!
nikisixx21
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January 15th, 2021 14:00
That solved it TY!
1) On the S2721Q the desktop resolution showed as 1440p while the active signal resolution showed as 4K 60. When I dropped the refresh rate down to 30 the flickering stopped.
2) Took your recommendation and put the S2721Q on 4k 30 and it's also now working as expected!
Definitely was a bandwidth thing. If I need 4k 60 on the second I will have to use one of the additional HDMI inputs.
Thanks Again!
nikisixx21
3 Posts
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January 15th, 2021 14:00
Got it. For this setup the daisy chain is only active for work which is mostly MS office so 30hz is fine.
I really chose to replace the P2720D with this to take advantage of the Xbox capabilities while I’m also at the desk. That will be over hdmi so should be able to enjoy 4K HDR and VRR. Thanks again.