820-01958 no backlight after closing and opening the lid

[Narek]

I got an water damaged MacBook Air A2179 with 820-01958 board.

The liquid affected areas were (pictures in attachments):

• USB-C controllers and D3302/3322
• Q8401/ R8400 along with with backlight caps
• U6500 area
• Trackpad electronics
• Audio board connector eaten away as always
• J6100 had some corrosion
• Water stains at left bottom corner of LCD

So I have replaced all damaged SMD components, reballed USB-C controllers, repaired trackpad and audio board, replaced J6100. After that computer turns on and works normally but time to time screen goes black by itself and not turning back on. The same when I close the lid and open it, backlight won’t appear, but computer is working. What I have done so far:

• Tried new Audio board with new flex cable
• Tried new right speaker with LID sensor
• Tried new mic/ LID sensor cable which goes under left speaker
• Tried new trackpad and trackpad flex cable
• Tried new LCD assembly
• Tried with keyboard disconnected

U4850 / U4802 areas were inspected - no damages found there, resistors around have correct values, there is continuity between all resistors in that circuit.

I’m on my leave now and don’t have board around, so I will write aproximate measurements which I remember, but they aren’t 100% correct. Tomorrow I’ll be in the office and update if necessary

SMC_LID_LEFT reads ~0,350V (diode mode)
SMC_LID_RIGHT reads ~0,350V (diode mode)

When lid is open SMC_LID_LEFT is 1,8V but SMC_LID_RIGHT is 0,9V and the backlight is present. Wen I close the lid both are 0V, and after opening they read 1,8 and 0,9V again but there is no backlight on the screen.

If I put computer to sleep mode from the system without closing the lid computer wakes up with backlight after pressing any button on keyboard. But if I will close the lid and open it up in some time computer wakes up without backlight.

 

[2informaticos]

"SMC_LID_RIGHT is 0,9V"
There is the problem.

You can bypass the problem removing R4805 and joining LID_OPEN_LEFT/RIGHT.

 

[Narek]

I've been thinking about that, but haven't tried yet. Do you think there is another way to return SMC_LID_RIGHT to 1,8V? There is no short on this line nor resistors have bad readings...

 

[2informaticos]

The pull-up resistor for SMC_LID_RIGHT its placed on the Hall sensor.
So you have a problem with the sensor itself, or continuity problem with connectors, or some cable.

 

[Narek]

Interesting, I have replaced all components related to that line (right speaker which includes hall sensor, audio board with new flex cable, J6100 which was corroded) and nothing has changed. I'll test your solution tomorrow and let know about results.