Why is the LCD turning off in a low light enviornment?

[AC Question]

Hi All,
I friend had given me their VS980 that had a broken digitizer glass, the top area to be specific.

After replacing the LCD assembly, everything worked great, except for one thing: it does not stay powered on in low light conditions.

If I press the power button on the back or double tap the screen, in normal room lighting or daylight, it's fine. (the display stay on and works as expected)
If I turn off the lights and its dark in the room, the LCD is powers on for maybe 1/2 to 3/4 of a second and then turns off. this behavior is very consistent.

Likewise, when I turn the room lights back on and place my finger over the ambient light sensor, the LCD does not stay on when I press the power button or use KnockOn.

I disassembled the phone again in search of anything abnormal but nothing stuck out at me.
I am unsure if this was a pre-existing problem when the phone was given to me or if there is another problem, perhaps caused by me.
Hindsight is 20/20, next time I have to check all functionality before I dig into it.

NOTE: After I successfully replaced LCD/Digitizer assembly, I did a factory reset. Also the indicators show no signs of water damage.

I'm wondering if I should replace the ambient sensor, or is it possible it could be a problem with the upper main board or even a software issue?
Thoughts?

Thanks in advance
-mike

 

[Rukbat]

It could be any of them. If the automatic brightness is on, and its bottom setting is too low, the LEDs will be off instead of very dim (there's a certain minimum dimness they can get to before being off). That could be bad hardware (sensor, motherboard), bad firmware ... a lot of possibilities.

Turn off automatic brightness.

Try running Velis Auto Brightness, so you can set the brightness floor.