820-01700 - No backlight.

[ronaldo]

H, everyone.
I've received it to repair as liquid damaged.
Dead board and after some work and jump wires on R5620 pins 3 and 4 to it's test points and cleaning, it now turns on.
Bad liquid on LCD connector and no display.
EDP_INT_AUX_N shorted. Fixed by replacing the U9850 MUX converter. It now has display, but no backlight. External display works fine and boot to the system.
Tested with another working LCD and LCD flex cable.
No short on backlight circuit fuse F8400 ok.
PPVOUT_S0_LCDBKLT - 0V - 178K
LCDBKLT_FET_DRV_R - 0V

U9801 - EDP_BKLT_EN - 0V
Diode mode - EDP_BKLT_EN - 0.542

PP1V8_S5_GPIOX_R - 1.8V
PP3V3_S5_GPIOX_R - 3.3V
EDP_PANEL_PWR_EN - 3.3V
R1528 - EDP_IG_BKLT_EN - 3.36V

I also replaced U980.
I run out of knowledges please, help.
Thanks

 

[2informaticos]

Inspect for corroded components in the backlight circuitry.
Pay atention to resistors and traces near U8400; you may need to resolder, or replace it.

 

[ronaldo]

Diode mode measurements on RB923 pin 1 were incorrect, but resistor is OK.
U8400 resoldered.

Backlight is on.
Thanks

 

[ronaldo]

For some reason, the backlight stopped again.
No idea what's going on here.

 

[2informaticos]

Check all resistors value and resolder them.