[GTALUG] flickering [was Has the graphics-card world gone mad?]

[Russell Reiter]

On Sun, Apr 4, 2021 at 10:26 AM D. Hugh Redelmeier via talk <talk at gtalug.org>
wrote:

> | From: Evan Leibovitch via talk <talk at gtalug.org>
>
> Thanks for the more complete information.
>
> What the exact brand and model of your Radeon RX 550?  Are you sure
> that the HDMI port conforms to HDMI 2.x?
>
> Remember that I'm not an expert.
>
> Jose Dias' experiment seems worthwhile.
>
> | The left (HDMI) screen will (randomly to me) do one of a few things:
> |
> |    1. Go off (the monitor reports lost signal) and back on after about
> 1-2
> |    seconds.
> |
> |    2. Go off (no signal) for 3-4 seconds and then back on, briefly to
> flat
> |    green or static and then normal.
>
> I would perhaps call that briefly blanking out.  There is probably an
> accepted term for this but I don't of know one.
>

Screen blanking is a feature of dpms, could try turning it off for the
monitor.


> I doubt that that symptom has anything to do with the compute power of
> the GPU.  It "feels" more like the monitor has been unhappy with
> something about the signal itself.
>

I ran into similar problems with a dual monitor setting up IOMMU / Vt-d on
intel. Blanking
the primary boot screen and no display on the other on boot up.


> Some video cards have fewer clocks than outputs.  Some outputs were
> required to share clocks.  This could cause mysterious problems.  I
> have no idea if that is the case here.
>
> Are you sure that HDMI is driving your left monitor at UltraHD
> resolution at 60Hz?
>
> | I've tried different cables, no difference.
>
> That would have been my first suggestion.  I once had a mysterious
> problem fixed by a new HDMI cable.  HDMI is complicated and made more
> so by papering over the complexity.  As HDMI bandwiths increase, more
> marginal cables fail.
>
> Are any problems logged by the system about the time of these events?
> (The few times that I've tried to understand a Windows log have been
> very unpleasant and not at all useful.)
>
> Experiment: shut down the system, disconnect the right screen, and
> reboot.  Does it flicker?
>
> Experiment: switch to mirroring (where each display shows the same
> thing).  Does it flicker?
>
> Experiment: try running both monitors at a slower refresh rate.
> Does it flicker?
>
> Experiments: try running the monitors at a different refresh rates (if
> that's possible).  Left slower than right.  Also left faster than
> right.
>
> Experiments: try the same set of experiments, this time varying the
> resolution rather than the refresh rate.
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-- 
Russell
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