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Strange Display / Screensaver Problem

Posted on 2011-03-21
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Last Modified: 2012-05-11
Hello!

I'm having a strange problem with an Ubuntu machine connected to an LGE flatscreen TV via RGB / VGA cable. I don't know if it's a screensaver or a power saver problem, but after 10 minutes on, the screen will black out and show a "no signal"-on-a-black-screen screensaver.

Then, when I switch the TV to another channel and back again to RGB input, the Ubuntu screen will come back, but will go black again after 10 minutes.

There is no input device connected to the Ubuntu machine (i.e. no mouse, keyboard).

I have Ubuntu configured to capture a screenshot every 15 minutes and have it uploaded to one of my web servers. According to the screenshots, everything is fine, but yet the screen is showing "no signal" on a black background.

"/apps/gnome-power-manager/timeout/sleep_display_ac" is set to "0" (never)

I also had dpms disabled like so:
/usr/bin/xset -dpms -display :0

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I'm now going to try and enable dpms but set all the timeouts to 0 like this:
/usr/bin/xset -display :0 dpms 0 0 0

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I'm not sure if that will work though. Is there anything else I can try?

I'm sure it's not a problem with the TV itself because I had a different Ubuntu machine connected to it recently, and I didn't have this problem. I had to replace it because of a hardware fault.

Thanks for any help in advance!
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Question by:Julian Matz
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by:Duncan Roe
Duncan Roe earned 125 total points
ID: 35188040
The normal way of power-saving is to drop sync. A TV might well interpret that as "No Signal" - in fact my monitor does but unlike your typical TV it goes quiet after a few seconds. Interesting that changing your TV channel wakes up the Ubuntu X server - I have no explanation for that.
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by:TobiasHolm
TobiasHolm earned 375 total points
ID: 35188147
Hi!

Maybe there's a setting in the TV that dims the screen if the picture hasn't changed in 10 minutes? Does the picture change during the 10 minutes?

Regards, Tobias
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by:TobiasHolm
TobiasHolm earned 375 total points
ID: 35188169
Also, can you try connecting another screen to the computer and see if that turns off in 10 minutes as well?

Regards, Tobias
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Author Comment

by:Julian Matz
ID: 35192017
The picture is constantly changing. It shows a sort of looped slideshow of images and video. It's basically a digital information display. I can't connect another screen. Well, I could, but it would be a big hassle.

I need to check again to see if enabling dpms worked. I didn't get a chance yesterday to investigate, but will try and find out today.
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Assisted Solution

by:TobiasHolm
TobiasHolm earned 375 total points
ID: 35192481
Is the slideshow running on the web? Or do you have à special app for it? If it's a webb app you could try booting an Ubuntu Live CD and see if the screen blacks out after you have removed the screen power save/screen saver in Ubuntu.

Regards, Tobias
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Accepted Solution

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Julian Matz earned 0 total points
ID: 35316392
Sorry for the delay. It has been a little difficult to test and troubleshoot in the production environment, but from what I can tell, it's now working fine.

It looks like the following command actually did fix the issue:

/usr/bin/xset -display :0 dpms 0 0 0

So, setting everything to 0 seems to be preferrable over disabling dpms completely.
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Expert Comment

by:TobiasHolm
ID: 35316653
julianmatz, you can select your own comment as the solution to close the question.

Regards, Tobias
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Author Closing Comment

by:Julian Matz
ID: 35356950
I appreciate the help, thanks!
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