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Old 10-23-2018, 08:54 AM   #1
bobl01
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Screen goes blank when Moksha splash screen appears - need to press a button to regain it


I've got this trivial issue with a new install of Bodhi with Moksha. A few seconds after the Moksha splash screen appears, the whole screen goes blank and the backlight goes out. If I press either the screen dim or screen brighten button, then the screen relights, and it's clear that the desktop has continued to initialise. Normally it's ready to go.

It's not a show-stopper, but any ideas for a fix?
 
Old 10-23-2018, 12:04 PM   #2
the_waiter
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Location: Banská Bystrica, Slovakia
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Hello there

Let's try this trick

open the terminal emulator and paste this line:

sudo su -c "echo 620 >/sys/class/backlight/intel_backlight/brightness"

reboot your PC and tell me if helped

Stefan
 
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Old 10-23-2018, 04:46 PM   #3
bobl01
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Hi Stefan.

Thanks, but it hasn't made any difference. I checked that the brightness file contained 620 after I'd run the command. After the reboot, I still had the issue, and the brightness file had changed to 4856730 (but I have to press the increase brightness button to get the screen to relight). FWIW the max_brightness file also contains 4856730.

Bob
 
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Old 10-23-2018, 04:56 PM   #4
the_waiter
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We never give up

Hmm, let's try to do that via backlight module. Load it under module section. The bulb will appear on the shelf. Then go to settings via right mouse button and try to play with values.

https://i.imgur.com/7ctItEr.jpg

Stefan
 
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Old 10-23-2018, 05:29 PM   #5
bobl01
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Well, this is really weird. It hasn't fixed the problem, but something strange is happening!

The brightness slider is working backwards! With the slider at its highest position (and the little bulb icon illuminated), the screen is blank! But as I slide it downwards, so the screen gets brighter and the bulb icon seems to get dimmer! What's more, the value in the brightness file gets lower as the screen gets brighter, so that it heads up towards 4800000 as the screen gets dimmer, and heads down towards 242836 at maximum brightness.

And yes, I'm aware that these values conflict with what I said earlier in the thread.

I think I'm going to have a lie down, now.
 
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Old 10-23-2018, 06:00 PM   #6
bobl01
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More information...

After a bit more playing, in addition to the value in the brightness file going down for a brighter screen, I've also discovered that the dedicated bright/dim buttons on the laptop work as expected - but they don't update the brightness file! Also, immediately on power up, the screen brightness is set to a high value.

As an experiment I set the brightness on the bulb slider to a midway value, then rebooted the system. After booting up, it showed the desktop splash image, then a few seconds later, dimmed it but didn't kill it completely. The system continued to start up as expected. As best as I could tell, the backlight was at the midway level before the reboot.

So, here's what I think is happening. The laptop powers on at full brightness. During desktop initialisation, a high value is written to the brightness file, which perversely causes the backlight to go out. I then poke the screen brightness button which overrides the value written by the system, and the hardware turns the backlight back on.

Not sure where to go from here. Poking the brightness button to bring back the desktop isn't a major hassle and I can live with it. However, whether it's worth modding the backlight module to handle this extraordinary special case isn't a decision for me to make.

I suppose someone is going to ask... The laptop is an ancient JVC MP-XV841. It doesn't have a system clock - it has a hamster running in a wheel!

Thanks to Stefan for your help.
 
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Old 10-29-2018, 11:59 AM   #7
bobl01
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I marked this as solved because it's due to a hardware quirk on the particular laptop I'm using. Some problems can't reasonably be fixed by a software patch!
 
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