MacBook Pro Retina Late 2013 (820-3462) No Backlight Help

[grimacelord]

820-3462 came in for liquid damage. Keyboard needed replacing and the backlight is out. I have already replaced the keyboard, but am stuck on the backlight. Hoping someone here can help.

I have verified that it is indeed a no backlight problem by shining a light through the Apple logo on the back of the display. I can make out the screen.

The computer works fine when connecting to external monitor.

I cleaned the board of what little liquid spill I could see and found the backlight fuse to be blown. I replaced it. Still no backlight.

I replaced the backlight driver IC (LP8545SQX-EXTJ, U9701) - Still no backlight.

Measurements (Battery not connected only power adapter, display cable connected.):

Pin 1 of J9000 - 12.56V
F9700 - 12.56V on both sides
Pin 4 of Q9706 (PPBUS_S0_LCDBKLT_FUSED)- 12.56V
Pin 1 of Q9706 (PPBUS_SW_LCDBKLT_PWR) - 12.51V
Pin 1 of L9710 (PPBUS_S0_LCDBKLT_PWR) - 12.51V
Pin 2 of L9710 (PPBUS_S0_LCDBKLT_PWR_SW) - 12.51v
Pin 1 of D9701 - 12.58V
Pin 2 of D9701 - 12.51V
Pin 21 of U9701 (BKL_FB) - 0.1V
Pin 4 of U9701 (BLK_EN) - 3.08V
Pin 2 of U9701 (LVDS_BKL_PWM_RC) - 3.32V
Pin 2 of C9719 - (PPVOUT_S0_LCDBKLT) - 12.58V


I'm stumped. Can somebody guide me from here? Thanks.

[piernov]

Re: MacBook Pro Retina Late 2013 (820-3462) No Backlight Help

Feedback line is broken. Either R9708 is bad or the trace/via between PPVOUT_S0_LCDBKLT and R9708 or between R9708 and pin 21 of U9701 is broken. Check R9708 and run a jumper wire where you don't have continuity on the line.

[grimacelord]

Re: MacBook Pro Retina Late 2013 (820-3462) No Backlight Help

Feedback line is broken. Either R9708 is bad or the trace/via between PPVOUT_S0_LCDBKLT and R9708 or between R9708 and pin 21 of U9701 is broken. Check R9708 and run a jumper wire where you don't have continuity on the line.

Thanks for helping me.

Alright, I ran a jumper wire from Pin 1 of R9708 to Pin 2 of D9701, checked for continuity along PPVOUT_S0_LCDBKLT and I had it, so I connected LCD and powered on - still no backlight.

I took a new voltage reading of Pin 21 of u9701 and now it reads 5.82v.

What now?

[grimacelord]

Re: MacBook Pro Retina Late 2013 (820-3462) No Backlight Help

Anybody?

[piernov]

Re: MacBook Pro Retina Late 2013 (820-3462) No Backlight Help

Still have image? D9701 not shorted? Q9701 not shorted? No other traces corroded (especially to Q9701)? If so it should work, measure voltage again on U9701, maybe something else is wrong.
Try a PRAM reset too.

[grimacelord]

Re: MacBook Pro Retina Late 2013 (820-3462) No Backlight Help

Still have image? D9701 not shorted? Q9701 not shorted? No other traces corroded (especially to Q9701)? If so it should work, measure voltage again on U9701, maybe something else is wrong.
Try a PRAM reset too.

I still get an image, yes, but no backlight.

D9701 readings:

Diode mode reading of Pin 1: 0.891
Diode mode reading of Pin 2: 1.071

I see no additional corrosion on the board.

Where should I measure to check for short on Q9701? I know a little bit, but this level of stuff is kinda new to me. Thanks again for helping.