Monitor keeps flickering after adding a second monitor

9
Posted 19th Feb
Hi, I have a 2nd monitor that I’ve added to my PC set up.

It doesn’t have HDMI, but only has DVI-D and VGA. My GPU doesn’t have VGA, so I used a HDMI to VGA cable to connect it to my GPU.
My main monitor is connected to GPU via DVI-D.

GPU is RX 570 4GB and only has 1x DVI-D, 1x HDMI and 2x DisplayPort.

Main monitor is 144hz, second is 60hz.

I’m having issues with the monitors both flickering.
I’ve read online that it could be an issue with a bad cable or it’s because they’re different refresh rates.
I’ve tried some methods, but they don’t work and my main monitor doesn’t have FreeSync.
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Hdmi to vga is digital to analogue so maybe that's the problem.
HDMI has no support for outputting a VGA signal, so if you're getting a picture at all then it's a converter box rather than a simple cable.

Although it's a odd choice to use the monitor's VGA input given that both DisplayPort and HDMI can effectively output DVI signals (DisplayPort through a feature called dual-mode, HDMI as it was built on DVI).

Can you describe the flicking in a bit more detail? Is it dimming or losing the picture? What frequency is it? Is it constant or occasional? etc. etc.
Edited by: "EndlessWaves" 20th Feb
EndlessWaves19/02/2020 22:42

HDMI has no support for outputting a VGA signal, so if you're getting a …HDMI has no support for outputting a VGA signal, so if you're getting a picture at all then it's a converter box rather than a simple cable.Although it's a odd choice to use the monitor's VGA input given that both DisplayPort and HDMI can effectively output DVI signals (DisplayPort through a feature called dual-mode, HDMI as it was built in DVI).Can you describe the flicking in a bit more detail? Is it dimming or losing the picture? What frequency is it? Is it constant or occasional? etc. etc.


I bought this cable:


Rankie HDMI to VGA Adapter with... amazon.co.uk/dp/…are

I used VGA as I had a VGA cable, plus the second monitor had no HDMI and only had VGA and DVI-D. Checked the driver for it, and the last it was updated was 2006, so it’s really old, but I thought I have it laying around, why not use it.

It’s flickering, like turning black for a few seconds and then going back to normal, then flickers again for like a good 5 min.

It’s occasional and happens about few times a day.

The second monitor is 60hz, 1680 x 1050 and my main is 144hz, 1920 x 1080
It's quite evident that it is impossible to synchronise 2 displays that is trying to render one bitmap where one display is refreshing its bitmap at a refresh rate that is not a multiple of the other display's refresh rate. When one monitor is refreshing 144 times a second and the other at 60, there will be periods in which the 2 displays are out of phase - that is while monitor one has refreshed the bitmap, monitor 2 is still in the middle of its refresh.

Let's take a more simple example. Assuming monitor 1 has a refresh rate of 3 Hz and monitor 2 is refreshing at 2 Hz. Monitor 1 will refresh the display every 0.33 seconds, while monitor 2 refreshes every 0.5 seconds. At time 0.5 seconds, monitor 1 has refreshed once (at 0.33 seconds) and is in the middle of refreshing for a second time (but yet to finish). Monitor 2 is just about to begin its first refresh. Now you see how this is out of phase. Yes there are workarounds for this but that is for another discussion. In practice, the 2 displays are not synchronised.

To keep everything synchronised, either set both displays to use the same refresh rate or set one display to use a refresh rate that is an exact mulltiple of the other (eg. set the 144 Hz display to 120 Hz and leave the other at 60 Hz, or set them both to 60 Hz).
That's not generally possible Elliot, and if it were it wouldn't cause the symptoms described.

With several seconds of blankness and both monitors being affected I suspect it might be windows and the graphics drivers trying to cope with the displays they're seeing varying - much like the screen goes black when you change resolution.

So my money would be on a faulty converter, or possibly a faulty monitor.
Don't use vga, it's analogue. Try it properly and use hdmi to dvi.
dcx_badass20/02/2020 11:18

Don't use vga, it's analogue. Try it properly and use hdmi to dvi.


The 2nd monitor has DVI-D and VGA only. So get a DVI-D to HDMI and then connect to my GPU?
EndlessWaves20/02/2020 11:14

That's not generally possible Elliot, and if it were it wouldn't cause the …That's not generally possible Elliot, and if it were it wouldn't cause the symptoms described.With several seconds of blankness and both monitors being affected I suspect it might be windows and the graphics drivers trying to cope with the displays they're seeing varying - much like the screen goes black when you change resolution.So my money would be on a faulty converter, or possibly a faulty monitor.


Could be a faulty converter as it was fairly cheap £4 on amazon, however it had 11,025 reviews, 4.5 stars.

However I’m assuming it’s a faulty cable as when I received it, it had marks of usage such as scratches. Possible that the previous user had it returned due to it being faulty.
jay.320/02/2020 11:29

The 2nd monitor has DVI-D and VGA only. So get a DVI-D to HDMI and then …The 2nd monitor has DVI-D and VGA only. So get a DVI-D to HDMI and then connect to my GPU?


Dvi and hdmi are both digital and the video signal is the same, so yes.
Edited by: "dcx_badass" 20th Feb
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