deloptes composed on 2018-05-15 20:43 (UTC+0200):

> I used till now DVI to connect the PC to the monitor. I recently bought a
> digitus 4K HDMI switch 4x1 to be able to switch between 3 HDMI inputs.

What model is that switch?

> However when I switched on the PC and X started, all was messed.
> Default resolution was 1280x720 instead 1920x1080. 
> The display area is partially out of the monitor size, so that the panel is
> not visible and lastly the quality of the image was really bad (like
> insufficient frequency or sync or whatever)

> I switched back to the DVI cable and I am wondering if someone can point me
> to the right direction.

IME, most manufacturers of HDMI switches are incapable of making them work
correctly - unless they do NOT include and automatic switching mode. Apparently
they think everyone who uses them turns HDMI devices off when not in use
(selected as the output by the switch).

The only one I've ever encountered that works reliably has no automatic
switching function and is a long ago discontinued model.

Other than returning the switch as "defective", I can only think to suggest two
things:

1-power off all HDMI sources except the one you wish selected, then cycle the
power to the switch.

2-manually configure Xorg using xorg.conf to exclude possible modes except
1920x1080. (Set PreferredMode, and set HorizSync and VertRefresh to narrow
ranges that can only compute to the 1920x1080 mode published in the manual or
provided by EDID when connected without the switch inline).
-- 
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