820-01598 Backlight Issues

[skc224]

Working on an A2159 (820-01598) that came in with physical damage to the LCD assembly near the hinge/screen bevel (see attached).
The board itself appears pristine with no signs of corrosion or liquid damage.
Tested with known good LCD assembly and the backlight is still out.

Measurements so far (bare board):

PP5V_SOSW_LCD --- 5V
F8400 --- 12v, 0Ω
PP3V3_S0SW_LCD --- 3.3V
D8410 pin 1 --- 5V
D8410 pin 2 --- ~33mV
EPD lines from J8500 all appear to be good, no shorts to ground.

It seems the backlight circuit for these is significantly more complex than for previous models. This thread may have been a similar issue, but it was never resolved.

Any advice would be greatly appreciated.

 

[2informaticos]

"Measurements so far (bare board)"
Did you measure backlight area without LCD connected???

 

[skc224]

That I did!

With the LCD connected measurements are as follows:

PP5V_SOSW_LCD --- 5V
F8400 --- 12.7v, 0Ω
PP3V3_S0SW_LCD --- 3.3V
D8410 pin 1 --- 0.2V
D8410 pin 2 --- ~0V
EPD lines from J8500 all appear to be good, no shorts to ground.

 

[skc224]

I checked Q8400 as it's the next thing upstream from D8400 which was the only component that appeared different.

Q8400

pin1: 0V
pin2: 0V
pin3: 12.6V
pin4: 12.6V
pin5: 0V
pin6: 0V

Looking at C8410 i'm getting 0V from ppv_s0sw_lcdbklt, and c8401 is running at about 0.5V on both pins.

Am I on the right track here?

 

[2informaticos]

First, I can't find Q8410 in schematic.
The 6 pins violtage don't match with Q8400, nor Q8401.
Please post accurate information!

BTW, ALWAYS check video/backlight related voltage/signal ONLY with LCD connected.

 

[skc224]

Sorry, fixed the typo in the post. Those were the measured voltages from the 6 pin Q8400.

 

[2informaticos]

As per shematic, pins 1, 2, 5, 6 are tied together.
You can compare with any similar SOT23-6 MOSFET.
Please, post CORRECT information!