820-00165 no backlight

[No-Clean]

I know no backlight....

I watched a few videos and have learned some but I cannot get this board to give me backlight.

Replaced Q7706 and U7701 and nothing.

BLK_PWM is 0.509v even after replacing U7701

 

[JohnB8812]

What voltage on BKLT output?

 

[2informaticos]

BKL_PWM controls U7701, not viceversa!
Post BKL_EN level too.

We need more info to help.
Post voltage and diode mode to ground on both pins of D7701.
Be aware of XW7720; pictures can be found on the forum.
Do you get image at least (on internal LCD)?
External video OK?

 

[No-Clean]

BLK_ISEN 0.008v

 

[No-Clean]

Not sure if you get a notification when I reply as a comment, let me know.

 

[JohnB8812]

No we do not. Please only reply. Let me be more clear. Post voltage on C7797. If 8.59 volts, then something wrong with feedback/the LED driver.

 

[2informaticos]

If you've changed U7701, post now diode mode (red probe at ground) on all return resistors.

Do PRAM reset few times.
If BKL_PWM still low, then remove R7704 and run a wire from R7715 to C7704.
Check if backlight comes on.

 

[No-Clean]

JohnB8812 C7797 indeed is 8.56v

2informaticos all return resistors measure 0.630
R7704 is 0.504v
I ran a wire from R7715 to C7704 after removing R7704 and no backlight either, folder with question mark flashes when I use a flash-light but no backlight yet.

 

[2informaticos]

Did you try known good compatible LCD assembly?

 

[No-Clean]

Yes, good know compatible LCD.

I put a new LP8550 and all is working again, thanks 2informaticos and JohnB8812 for all the help.