820-01598 No backlight

[yair37]

no water damage, the mac was fall...
screen o.k replace cable also.
F8400 is good. EDP_BKLT_EN is at 3.3V
D8410 measurements are good.
1) 1.116
2) .800
BKLT_SCL 5.1v
BKLT_SDA 5V.
all really look good.

 

[2informaticos]

Do you get image on internal LCD, only missing backlight?
Be aware, dropped machine is a nightmare...

 

[yair37]

i was put other board instead and it work fine and also work with external screen...only backlight! there is picture.

 

[2informaticos]

Probably broken traces, or solders.

 

[yair37]

Where to search? All BKLT lines?

 

[2informaticos]

Did you change the small video flex from MLB?

 

[yair37]

Did you change the small video flex from MLB?

The second thing that i did..

 

[2informaticos]

Do you get any voltage at D8410?
Don't forget to check with internal LCD connected.

 

[yair37]

Do you get any voltage at D8410?
Don't forget to check with internal LCD connected.

No

 

[2informaticos]

Please, stop to quote an entire post visible few centimeters above.

What about BKLT_SD?
Tried PRAM reset?
Resolder all around U8400 and check the traces.

 

[yair37]

What about BKLT_SD?

10.8V

Tried PRAM reset?

not working.

Resolder all around U8400 and check the traces

alll look good and also replaced the U8400 but the same..

 

[2informaticos]

BKLT_EN_R must be high.
But U8400 is controlled through I2C bus from PCH, via LCD panel.
Check all R8450-52 resistors and traces.
Post voltage and diode mode to ground at SCL/SDA lines.
Also check traces from J8500 for any BKLT signal.
Do you get any voltage at EDP_BKLT_PWM?

 

[yair37]

BKLT_EN_R must be high.

is 3.3v

Check all R8450-52 resistors and traces.

its looking good. compare with good know board.

Post voltage and diode mode to ground at SCL/SDA lines

SCL/SDA 5.1V

Also check traces from J8500 for any BKLT signal.

YES ALL GOOD

Do you get any voltage at EDP_BKLT_PWM?

2.5V

 

[2informaticos]

"and diode mode to ground at SCL/SDA lines."
???

Possibly bad contacts at J8500.
Did you check traces between R8450/51 and J8500 and U8400?

 

[yair37]

"and diode mode to ground at SCL/SDA lines."

I was compare with good board but anyway....SCL 512 - SDA 520

Did you check traces between R8450/51 and J8500 and U8400

YES IT ALL GOOD!
why i dont have V on D8410 and Q8401

 

[2informaticos]

Because U8400 MUST tie BKLT_SD to ground first.
And depends by I2C_BKLT bus.

 

[yair37]

so to soldering j8500 and resoldering u8400?

 

[2informaticos]

You should check conectivity from J8500 to other components.
But this will not allow you to discard bad connections inside of J8500; with the small flex.
May need to check continuity from the other end of small cable, to the MLB components.

 

[yair37]

I was check all the BKLT continuity and thay all fine(but I will do recheck), do I need to check all the J8500 connections?
I have other same good board so I check with it also..

 

[yair37]

changed U8400 again and BOOM! backlight is back!
thanks!