820-00281 Backlight on and off

[No-Clean]

Clean board, about 8 months ago had issues around U4200 that got fixed and now is back with backlight issues.

Backlight works on and off even with different screen, should I be thinking U9800 is to blame?

 

[2informaticos]

Steady image on internal screen, only missing backlight?
Check Hall sensors (LID) signals.

 

[No-Clean]

Yes, steady image, when the problem occurs PPVOUT_S0_LCDBKLT is 0v
I also noticed that the power button is no longer working, SMC_ONOFF_L drops to 0V from 3.4V when the button is pressed, but nothing happens.

 

[2informaticos]

DP_INT_HPD steady high?

 

[No-Clean]

Well now I have steady backlight and can no longer troubleshoot, but I know it will fail sooner than later, I will be back.

 

[No-Clean]

Ok I am back, to replicated the issue I had to close the lid then open and backlight is gone, some other times it is gone from the start.

DP_INT_HPD 3.2V steady even with no backlight.

 

[2informaticos]

This looks like flexgate issue, if related with screen movement.
An issue with Hall sensors should affect image also.
But check LID signals, just in case.

 

[No-Clean]

SMC_LID is 0V when lid is closed and 3.4V when the lid is open.

 

[2informaticos]

Need to check when backlight fails.
Don't forget LID_LEFT/RIGHT signals.

 

[No-Clean]

I just tried opening and closing the lid several times but not all the way and backlight remained steady, as soon as I closed the lid all the way once backlight was gone.

How do I measure under the board with screen connected and battery connected? I have a test display but when testing that way with no battery the battery icon comes on and is gone in seconds and I cannot test this issue. For DP_INT_HPD I had to solder a wire to measure on the other side, I guess I will do the same, any tips are appreciated.

 

[2informaticos]

Disconnect J5250/60 and see if problem persists.

 

[No-Clean]

Both removed, still no backlight and now backlight is gone from the start, but that was also happening before.

One thing I noticed is that when lid is closed fans continue to spin.

 

[2informaticos]

Fans still spin, if Hall sensors are disconnected; SMC cannot detect the lid is closed.

 

[No-Clean]

This was happening before I removed the sensor, but this tells me something, I will replace them and see what's up.

 

[No-Clean]

I replaced both sensors and problem fixed, both power button and backlight are back to normal, thanks @2informaticos