[SOLVED]820-2936 no backlight

[RyanLEN]

Hi. I have a 820-2936 with no backlight with 12.5 volts on pins 21 & 22 of J9000. After changing LP8550 I still have 12.5 volts on output. Thanks for any help in advance.

 

[aprendiz]

check feedbak trace, also chek R0910.....

 

[dukefawks]

BKL_EN and PWM?

 

[RyanLEN]

Hi. Thank you for the responses. FB is 12.5, R0910 is 12.5 pin 1&2, BKL EN is 3.1 and 0 PWM is 0. Thanks.

 

[aprendiz]

Check R9704, do you have any voltage on LCD_BKLT_PWM??

 

[RyanLEN]

No I do not.

 

[RyanLEN]

should I remove the driver and check again?

 

[aprendiz]

LCD_BKLT_PWM comes from PCH, check this line on diode mode.....

 

[RyanLEN]

4.30 in Diode.

 

[aprendiz]

Red probe to ground and black on LCD_BKLT_PWM??

 

[RyanLEN]

Im sorry. I have .58 on LCD_BKLT_PWM from via.

 

[RyanLEN]

removed driver and still 0 on LCD_BKLT_PWM.

 

[RyanLEN]

I'm assuming PCH is at fault and nothing else can be done. Ended up running a wire from C9711. Thank you very much for your help.

 

[RyanLEN]

Now having a more problems related to BKLT after running wire. every 10 -15 seconds durring OS install the screen will go to sleep and I will have to press the power button to wake it up. Any thoughts?

 

[TCRScircuit]

Your issue was never with the PCH or backlight circuit. Your PWM is missing because it think's it's sleeping. Try a new Magsafe board as that has the sleep sensor on it.

 

[aprendiz]

The sleep sensor is on the battrery light indicator.... Remove the BIL and check is SMC_LID is high......

 

[TCRScircuit]

You are right!

 

[dukefawks]

SMC_LID issue. So either the battery indicator or the pull up resistor on this line R5071.

 

[RyanLEN]

Holy Shit! Hahaha... I'm such an asshole! Here I am dicking around trouble shooting a logic board, when the whole time it was the Batt Indicator as you guys pointed out. I pulled one from another machine and everything is up and running. What a dildo. Thank you Aprendiz, TCR and Duke. Much appreciated. Have a good one!