820-3437 no backlight

[iClub]

all right buddy ? I have this defect and several times I used the LP8550, I used 820-3115 scraps board and macbook air, but I did not succeed. I imagine it has some relation with EFI password.

Voltage: PPHV_S0SW_LCDBKLT 8.48v ~0v; LCDBKLT_EN_DIV_L 2.84V; BKL_PWM 2.50v;
PPVIN_S0SW_LCDBKLTFET 8.6V.

 

[2informaticos]

Looks like U7701 gets correct adjust control; you didn't mention enable signal, BKL_EN.

"PPHV_S0SW_LCDBKLT 8.48v ~0v"
Please take your time and describe exactly the symptom.
I can supopose PPHV_S0SW_LCDBKLT drops from 8.4V to 0V.
But that is not possible if
"LCDBKLT_EN_DIV_L 2.84V".
which should go high to 8.4V in such case; unless Q7706 is bad.

Possibly to have problem with XW7720; detailed explanations on the forum.

I used 820-3115 scraps board and macbook air, but I did not succeed"
I cannot understand what you really mean...

 

[iClub]

WITH AND WITHOUT THE LCD CONNECTED The voltage present in the mesh PPHV_S0SW_LCDBKLT 0v; PPVIN_S0SW_LCDBKLTFET 8.6v; LCDBKLT_BOOST 0v;
I used the ci backlight of discarded boards, such as macbook pro 13 2012 and other air macbook.

the line pp5V_S0 is short when I change the LP8550.

 

[2informaticos]

That is BGA chip, can you be sure about good soldering of reused chips???
Be serious man, that chip is 1-2 bucks new!
You just shorted 5V_S0, because of bad solders underneath...

 

[iClub]

I changed the new lp8550, in the tests it is not showing any image or background light, any suggestion of what it might be ?

 

[iClub]

It doesn't give an image on the outside.

 

[2informaticos]

Do you have image on internal LCD for sure?
If not, no reason to bother with backlight.
I explained several times, image must appear before backlight.
You don't get external video, did you check USB activity?