[SOLVED] A question about X and monitors: need explanation, not help ;-)

hazel · 07-10-2021, 09:02 AM

Having carted off my failing 19" monitor to the dump, I slotted in a 17" one as a temporary replacement. It made everything look much smaller (text characters expecially) and the colour rendering was unreliable, with the blue signal switching off after a while and everything coming up yellow. So I decided that the vga cable must be faulty and replaced it with the one from the 19" screen instead.

Now the colours are fine, but what surprises me more is that everything is back at normal size and has a nice crisp appearance. So I checked today's Xorg.log and compared it with yesterday's. I found this:

Code:

New
[    61.358] (II) intel(0): switch to mode 1024x768@60.0 on VGA1 using pipe 0, position (0, 0), rotation normal, reflection none
[    61.376] (II) intel(0): Setting screen physical size to 270 x 203


Old
    54.508] (II) intel(0): switch to mode 1280x1024@60.0 on VGA1 using pipe 0, position (0, 0), rotation normal, reflection none
[    54.510] (II) intel(0): Setting screen physical size to 338 x 270

Why should changing the cable make such a difference to the way the computer sees the monitor?

michaelk · 07-10-2021, 10:08 AM

I can only assume that the old cable was not wired correctly or had some missing pins/wires which caused the system to not read the monitor EDID information correctly if at all.

hazel · 07-10-2021, 12:08 PM

Here's how the old X log went on EDID

Code:

[    56.257] (II) intel(0): EDID vendor "FUS", prod id 1350
[    56.257] (II) intel(0): Using EDID range info for horizontal sync
[    56.257] (II) intel(0): Using EDID range info for vertical refresh
[    56.257] (II) intel(0): Printing DDC gathered Modelines:

and then a whole lot of mode lines. The current log doesn't have any of that.

obobskivich · 07-11-2021, 11:00 AM

Quote:

Originally Posted by michaelk

I can only assume that the old cable was not wired correctly or had some missing pins/wires which caused the system to not read the monitor EDID information correctly if at all.

This would be my guess as well, but if I'm reading your logs right, its actually running at a lower resolution now. If these are both 17" 5:4 SXGA monitors, the 17" will have a finer pixel pitch (or higher DPI) and things should be relatively 'smaller' as a result, but running it at a lower resolution may 'fake' that back out (but if that's the case, you're not feeding it the proper aspect ratio now either). It also shouldn't ask for an arbitrarily lower/incorrect resolution - but I'll admit I'm making an assumption that they're both 5:4 SXGA monitors (because that tends to be the most common for a 17" display in my experience).

hazel · 07-11-2021, 11:05 AM

They aren't the same size. The previous one was 19" and this one is 17".

1024x768 is the resolution the old 19" monitor ran at. I recognise the figures.

obobskivich · 07-11-2021, 11:09 AM

Quote:

Originally Posted by hazel

They aren't the same size.

Sorry for being unclear - I'm working on the assumption that they're the same resolution (specifically SXGA) - is that not the case?

hazel · 07-11-2021, 11:15 AM

Quote:

Originally Posted by obobskivich

Sorry for being unclear - I'm working on the assumption that they're the same resolution (specifically SXGA) - is that not the case?

They seem to be set to the same resolution now with the change of cable and everything looks the same size as before. Previously, the replacement 17" monitor was clearly running at a higher resolution and everything looked shrunk and crowded. I'd just like to know why it did that. And also why the colour went berserk.

EdGr · 07-11-2021, 12:04 PM

The lack of EDID information makes me think that the new cable may be missing the EDID pins (which means that it is actually very old).

The strange colors with the old cable means it is defective.

Neither cable works.
Ed

mrmazda · 07-13-2021, 02:07 AM

I've run across lots of VGA cables with only 14 connectors available. Some displays just don't like to behave as expected without all 15 in working order.