Armbian - need help, locked out myself by setting backlight to zero

Armbian has an issue, that it's possible to set backlight to zero, effectively blanking the screen completely. Accidentally, I've pulled the slider in XFCE too much and disabled the backlight completely.

Unfortunately, I'm not sure, how to fix this, because systemd launches unit "restore backlight levels" during the bootup and turns the backlight off right on the boot.

This wouldn't be a much of a problem, but I'm currently on a trip, and I have no MicroSD with another OS to fix the problem (Armbian is installed to eMMC). Somehow, I need to disable backlight restore service, or go into single-user mode, so that I can edit the configuration, but all I currently have access to is an Android smartphone and U-Boot on the Pinebook. Serial console is not an option either.
It might be possible the screen backlight is not completely off but just extremely dark. I made the same mistake running KDE Neon the first time I was trying out my Pinebook and the solution was to shine a flashlight on the screen at the right angle where you could then actually see the desktop just enough to turn the brightness back up again.

Unless your backlight really is completely off. Then, unfortunately, I don't have any ideas besides wondering if there's a "safe-mode" you can switch to on boot? I'm not familiar with Armbian, unfortunately.
Report it to Armbian please.
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MECZero, thanks. When I did this first time, I couldn't see anything at all, but I tried it again and could actually see some things faintly under specific angles. Possibly, my smartphone flash is not bright enough. And Armbian's dark theme makes it worse, because top bar cannot be seen. But this is at least something. Will also try to use the tty to set the brightness (at least, it should have decent contrast).

Luke, OK, will post to Armbian's bugtracker a bit later.
Well, the problem is solved, thanks to MECZero, with more flashlight fiddling, I've found the right angle and found that you need to put flashlight very close (almost push it against the screen) to light it just enough to see icons on dark top bar.
It's not unique to Armbian, I've done it myself with the pinebook when playing with screen brightness. The fix is to either login via serial/network and tweak the right sysfs path,  or use a flashlight to light up the LCD panel enough to be able to use the screen again to turn the brightness up Wink  you just need to find a bright enough flashlight to be able to light the screen up enough... and yes, you basically put it right up to the screen, and shine it at an angle. 

This was why a brightness script I published a while back has end limits on it so that it can't turn the backlight off!  Big Grin Big Grin
(03-30-2019, 10:55 PM)pfeerick Wrote: The fix is to either login via serial/network and tweak the right sysfs path

for network - when armbian is normally iinstalled - it uses the network-manager.
so when you then insert a USB-Ethernet-Dongle this would use DHCP and you can connect via ssh.
Then you have to find/edit the screen setting.
Network access on the Pinebook would be much more easy than a serial-port-login , because a usb-serial-donge would automatically become a serial-terminal Wink

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