[SOLVED] 820-2850 no back light , not boosting

[roy.ruan]

having a 820-2850 board got liquid spilled,area around connector and led back light driver circuit.
got no back light.

PPVOUT_S0_LCDBKLT=12v , means not boosting.

checked:
D9701 both pins are 12v
lcdvdd en =3.3v
pwm= 0.3v
smc_lid=3.3v

pin 8 pin22 and pin 23 on u9701 all have correct voltage
changed connector and u9701 already.
feedback line trace is all good

only thing i can think of is the pwm signal is kind of low?
tried PRAM reset already.

any thoughts?

thanks

 

[TCRScircuit]

Corrosion under PCH probably. Throw it in the ultrasonic cleaner

 

[2informaticos]

"pwm= 0.3v"
Where did you measure?
Always specify the measure point.
If you have 0.3V at both pins of R9704 is not the same as you have 0.3V at pin2 and pin1 close to 3V.
I hope you understand what I mean to tell...
Now tell us which is your case.

 

[roy.ruan]

sorry for the confusion. both pins on r9704 are close to 0.3.
checked r9704, 0 ohm

but i really looked under the microscope around the PCH carefully, really don't see anything, it looks so fine...can't believe anything would leak in there..

 

[roy.ruan]

and isn't LCD_BKLT_PWM comes from U9600 the mux?

 

[dukefawks]

Fucked MUX probably. Remove R9740 and tie the PWM pin to 3V somewhere.

 

[roy.ruan]

it is a fucked MUX. just measure diode mode , on pin 1 r9704, only get 0.014, way too low, connected to mux directly. 99% is the mux...

don't want to mess with that POS. if I just jump 3v from some pp3v3 s5 rail, the brightness function keys won't work anymore right?

 

[roy.ruan]

you can mark it as solved, spent an hour replacing the mux. all good now. thanks guys