820-00165

[Anterweb]

In for no backlight,



I cleaned this up and replaced,

R7755
C7710
R7741

Left out C7714 as top pad was missing.

I have 3.42 at SMC_lid

tried Pram reset 3/4 times

Did a gentle reflow on U7701

Other side of board I get 8.55v at F7700 but on xw7720 I get 0v.
Does this look like a bad U7701?

Problem I have is a guy is driving a long way past me tomorrow to collect this and I dont have any U7701 chips left,.
Is there any way to bypass it and get a backlight working?

 

[2informaticos]

Be sure all the resistors in the area (opposite board side too) are good.
You can't boost the voltage without U7701.

Post BKLT_EN/PWM levels.
Also check Q7706/7 voltages.

 

[Anterweb]

LCDBKCT_EN_L =3.70v ( Seems to move up and down a bit to 4.5 then back to 3.7
PWM =0v

Q7706
1- .270v ( Seems to slowley drop )
2- 17.0mV
3 - 6.08v
4- 8.55v
5 - 1.940v
6 - 1.508v

Q7707
1- 0v
2 - 3.33v
3- 3.10v
4- 0
5 - 0
6 - 0

All resistors measure good

 

[2informaticos]

Sorry about signal names.
I meant BKL_EN/PWM.

"Q7707
5 - 0"
Since EDP_BKLT_EN is missing, backlight circuitry is not enabled yet.
Do you get image on internal LCD for sure?

 

[Anterweb]

100% get image can even shine scope through back of lid and log in.
BKL_EN = .233v
BKL_PWM = 00.3mV

This can't be related to me leaving out C7714 can it? cant see how!

just tried this logic in another known good machine same result all good can log in just no backlight

 

[2informaticos]

C7714 is not critical, forget it.

The big ptoblem there is missing EDP_BKLT_EN.
This can be caused by bad U7701, which can block communication with PCH through I2C bus.

 

[Anterweb]

Ill order some U7701 chips now and replace , thanks dude

 

[Anterweb]

Chips arrived today! Replaced U7701 and Boom! backlight returns!

Another one fixed. thanks dude,