Hello everyone

Good news, I started to disassemble the LCD and I discovered one cable disconnected (CNT201), just reconnected it and the backlight is working fine now.

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So many thanks mon2 for your help
Have a great day...

I did tested the following:

1. Connected external 48v LED strip the PPVOUT_S0_LCDBKLT line and the booster didnt work.
2. Injected LED tester @ PPVOUT_S0_LCDBKLT with 10mAmp and there was no current drawn from Retina LED.

Here I started to think the Retina display has a defective LED circuit and asked U7701 not to start boosting.

Is there anyway to test the Retina LED from external source ?

Any thoughts would be appreciated
Thanks...

Thanks alot agin mon2 for your follow-ups,


Already checked = OK


I think you meant to short BKLT_SD to ground, but I shorted pin#4 & pin#6 instead to bypass 12v to PPBUS_SW_BKL, and I got what I expected at PPVOUT_S0_LCDBKLT = 12v, which means the booster still wont work.



I think U7701 still get LCD not ready for LED power on, otherwise pin#11 (BKLT_SD) should start signaling right?...

Correction, I2C_BKLT_SCL = I2C_BKLT_SDA​ = 5.03v now, or maybe it is different slightly from time to time as it is a communication signals right ?...

1. Thanks alot for your reply and greetings mon2
2. My little multimeter from Uni-T and it has auto-mode feature and it starts with sensing ac/dc voltages first, and then it starts to look for resistance if there was no voltage detected (UT123D).
3. 4.78v , 5.03v and EDP_IG_BKL_ON​=3.33v coming via R7742 (0Ohms)
4. It gives 14Kohms and then goes to 500Kohms repeatedly, I even injected external power (50v) to insure no leakage and there was 0mamps.
5. Q7706: 12.66v@pin#3 , 12.76v@pin#4.

I think Q7706 will stay off till BKLT_SD goes down right ?

Thanks alot for your contribution
A...

Dears, this is my first post here and first try to fix my own laptop Apple MacBook Pro Retina 15-inch Mid 2015.
I have some general electronics troubleshooting experience and still as my hoppy but this is my first laptop trying to fix.

History: my laptop backlight stopped working without any reason.
Symptoms:
I have image on screen using my flashlight.
I have fully working laptop with the help of my external SAMSUNG LED tv via HDMI cable.
Keyboard backlight still working and can be adjusted normally.

Since two days I tried to follow all similar...

This is a great place to learn and share our knowledge in electronics!!!