820-4924-A backlight comes late

[ntcR]

Hi guys, I could use some help, can't get any further.
I swapped the display on an A1502 (820-4924-A) (2015). When booting, the screen has no backlight until the loading bar has reached about 80%.
I noticed that when I turned it on the charging cable (85W original) shows orange for a short moment, then green -> orange as normal. No idea if it have something to do with the backlight problem.
At C8303: 1 PPVOUT_S0_LCDBKLT I measure 49V at start (without backlight), as soon as the backlight switches on 40V.

 

[2informaticos]

First of all, welcome to the forum!

What's the problem of original LCD?
Connect it back and check how backlight starts.

 

[ntcR]

Thank you, nice to be here
The original display shows a picture completely without backlight, with another display the backlight turns on immediately. We tested all 3 displays with the same result on a different board.
Is there a way to fix the display with the late backlight?

 

[2informaticos]

So other screen has the same issue on this board?
Are you sure all of them are 2015?
Did PRAM reset 2-3 times?

 

[ntcR]

The 3 displays behave differently on this board. I tested the displays on another 820-4924-A board. The behavior of the displays remains the same, which leads me to assume that it is the display and not the board.

Can you tell on the display whether it's 2013/14 or 2015?

When replacing the display (backlight comes late) I reset the PRAM 5x. Should I reset the PRAM every time I change the display, or is that enough?

 

[2informaticos]

Nothing to lose if do it each time.

Any of the 3 displays gets backlight faster than other?

 

[ntcR]

I did each time. No changes.

Yes, one get backlight from the beginning (as usual), the second one when booting bar is at 80% and the third one never.

Ist there a way to see what type of Display I have (2014 or 2015)?

 

[2informaticos]

Then you have a LCD issue and must get the correct model.
The one which get fast backlight, is for 2015 .