820-3115 No Backlight Killing Me

[jadao]

Pin 3 should be way lower...something around 4V.
Could you check continuity (diode mode) between
pins 4 and 1-2-5-6?
pins 3 and 4?
EDIT: With no power applied of course.

 

[felixthecat]

No beep at all on all the Pins you asked.... I should just go run this over with my SUV a few times, pick up the remains and burn them and then bury it.....

Just for the heck of it I replaced C9782 as well...

Pin 3 now shows 4v still no backlight....

 

[jadao]

What voltage do you get at
pin 2 of R9789?
pin 1 of R9731?
pin 2 of R9731?
What resistance do you measure on R9731?
​​​​

 

[felixthecat]

pin 2 of R9789 - 12.03v then drops to 0.1
pin 1 of R9731 - 0v
pin 2 of R9731 - 0v
What resistance do you measure on R9731 - 301K

 

[jadao]

Ok you seem to have a break in the trace between pin 1 of R9731 and pin 1-2-5-6 of Q9706, so
Double check before and run a wire If no continuity, after that you should get around 3V at pin 2 of R9731 it's bkl_en.

 

[felixthecat]

Thank you for the suggestion, I didn't even notice the through the hole to other side was bad :-/
I have the 3v on pin 2 of R9731 still no backlight. I'm beginning to wonder if this board is just hopeless

 

[dukefawks]

You fixed a bad trace. Now you go back to step 1 and check voltages again on Q9706 and see if it at least fixed that.

 

[felixthecat]

Q9706

Pin 1,2 - 12.5v
Pin 3 - 4.3v
Pin 4,5,6 - 12.5v

BKL_EN - 3.1v
BKL_PWM - 3.2v

BKL Line LCD Pins 2,3,4 - 3.3v Pins 21,22 - 0.6v

 

[dukefawks]

R0910, D9701 or L9701 is/are bad. Or any traces between them. R0910 is a common one to corrode.