820-00165 Backlight Issue

[Instafixx]

No Backlight.I Have Image. Confirmed.

F7700/L7701/D7701is 8.56V

Backlight Feedback XW7720 is 8.56V.

BKL_EN is 2.8V
BKL_PWM is 2.8V

PPHV_S0SW_LCDBKLT is 8.5V

 

[2informaticos]

Did you check XW7720 continuity?
If OK, probably corroded balls under U7701.

 

[Instafixx]

How do i check continuity. This is not actually a part on the board

 

[Instafixx]

Meter in Ohms Mode
Red to PPVOUT_SW_LCDBKLT_FB
Black to PPHV_S0SW_LCDBKLT

I get 1.1 ohms

 

[2informaticos]

Looks good.
Possibly corrosion underneath U7701.

 

[Instafixx]

Removed - Cleaned and Re installed U7701. Still the same.

 

[Instafixx]

Have tried a known good display. its not a display issue

 

[2informaticos]

Did you check BKL_EN/PWM signals?
Also check all return resistors, R7717-22.

 

[Instafixx]

BKL_EN is 2.8V
BKL_PWM is 2.8V

Voltages
R7717 - R7720 is 2.3V
R7721-22 is 0.3V

Diode Mode Readings
R7717-22 is .634

Continuity
R7717-R7722 is 1.2 Ohms

 

[2informaticos]

"R7717 - R7720 is 2.3V
R7721-22 is 0.3V"
You should get almost same value on the six lines.
May have problems with the video connector; or traces from it to R7717-22.

 

[Instafixx]

Replaced U7701. Issue Resolved.