FIXED A1466 820-00165-A backlight problem

[isc]

only backlight flash for second then turns off
mother board is already repaired
backlight fuse shorted and J8300 due burn out replaced
I reset PRAM 3 times , replaced U7701 and Q7706 but not fixed
SMC_LID is good 3.3v
EDP_BKLT_PWM 1.47v
SMC_LID 3.42v
any suggestions ?

 

[2informaticos]

"J8300 due burn out"
LCD cable wasn't affected?
Did you test with known good LCD assembly?
Did you check XW7720 continuity?

 

[isc]

XW7720 is good
LCD cable was affected but i test at other good working lcd assembly

 

[2informaticos]

Do you get image for sure, only missing backlight?

 

[isc]

yes

Do you get image for sure, only missing backlight?

YES
THERE IS IMAGE

 

[2informaticos]

Check BKL_EN/PWM (U7701 side).
Be sure D7701 is not shorted A-K.
Post Q7706/7 voltages.

 

[isc]

BKL_EN 2.83V
BKL_PWM 1.47V

D7701 IS OK

Q7706 ALL pin 8.56V

Q7707
1 GND
2 1.03v
3 2.7v
4 2.21v
5 3.3v
6 2.21v

 

[isc]

only image and backlight comes on less than a second then turns off

video in drive link

https://drive.google.com/file/d/1exB2QGr9Qyc9aNhqdBXOx54-V2tmmYqU/view?usp=share_link

 

[2informaticos]

"Q7706 ALL pin 8.56V"
So is damaged, requires low voltage on pin 3; change it.

I have doubts about Q7707, or the posted readings.
Check R2088 and post U2071 voltages.

 

[isc]

I replaced Q7706 & Q7707 from good working board but no backlight
R2088 3.3v
U2071 voltages
1 3.32v
2 3.32v
3 0
4 3.32v
5 3.32v

 

[2informaticos]

"R2088 3.3v
.............
Q7707
2 1.03v"
This looks strange, don't you think?

Post again Q7706/7 voltages.

You may have bad solders for U7701.
Post diode mode to ground on all its connections.
Use surrounding components as test points.

 

[isc]

i replaced Q7706 ,Q7707 and U7701 and check R2088 0 ohm
now
Q7706 pin
1 8.4v
2 8.4v
3 7.9v
4 8.5v
5 8.4v
6 8.4v

Q7707 pin
1 0
2 3.3v
3 0
4 0
5 3.3v
6 0


also i check R7789 147k and R7788 300k

 

[2informaticos]

Q7706's pin 3 should have much lower voltage; aprox 2V only.
Just in case, remove C7782 and check again.
Be sure to solder Q7706 in correct orientation.
Is the replacement used P-channel MOSFET for sure?

 

[isc]

I removed C7782 but no change

Q7706 is correct and from working doner board

 

[2informaticos]

Did you check pin 3 voltage again?

 

[isc]

Did you check pin 3 voltage again?

yes the same value 7.9v no change
and i replaced Q7706 , R7788 , R7789 from other board and no way

 

[isc]

 

[2informaticos]

Please, calculate Vout (LCDBKLT_EN_DIV_L) voltage of R7788/89.
Consider LCDBKLT_EN_L is 0V and Vin=8.4V (PPVIN_S0SW_LCDBKLTFET) (as you've mentioned before).
I can't get 7.9V myself...

 

[isc]

i know LCDBKLT_EN_L it must be due volt divider 2.756 v
but when i force pin 3 for Q7707 to GND pin 3 for Q7706 is 2.8v and source & drain are 8.5v
i replaced all comunents above one time the pin 3 for Q7706 is now 2.8v
also only backlight flash millisecond then turns off
note:KB backlight not working also any suggestions?

 

[2informaticos]

Disconnect the webcam and test again; including KB backlight.

Why to force?
You've said to have 0V at pin 3/Q7707; change it, if in doubts.