820-00165 Keyboard backlight 4.9v

[TBFix]

Board originally was not recognizing webcam , I replaced U3900 as all voltages were present but forgot about clock signal (missing clock signal). Now not getting Keyboard backlight no voltage on enable to U7750 (0v on SMC_SYS_KBDLED), checked trace to smc was good, checked fb resistor and traces, good. Replaced smc still same. Tried clean bios and good keyboard backlight but still the same. Tries boot into different Os still no backlight.

Any help appreciated

 

[2informaticos]

ALS working?
Try known good LCD assembly.

 

[TBFix]

Yes I have tried working assembly previously. if U3900 is not good would that also cause this?

 

[2informaticos]

ALS connects to SMC.
Did you check if LCD backlight reacts when direct flashlight to webcam?

 

[TBFix]

Yes it has no effect. I have changed U3900 again and it seems to be working now . Just reassembling to fully test.