Dell E1709W - Power Issues: LED Off;No Display

Service Manual
30
Power (include IF +5Vand +3.3V) supply normal but LED off and no display
Power (include IF +5Vand +3.3V) supply and display normal only LED off
Is the frequency 14.318MHz at #2 of IF
Board U105?
Change crystal X101
Yes
Is the low active reset signal at #54 of
IF Board U105 normal?
Change C164
Yes
Is the serial clock signal at #6 of IF
Board U105 normal when power AC on?
Change U105
Yes
Change U105
Is the keypad cable connective OK
Reassembly or changing
Yes
Is theLED control signal at 60# of U105
high-low convertible when DC on/off
NO
NO
Change Q108
Is the key function OK?
NO
Press power key to DC on the monitor,if
display ok the process is end,if no display see
the no backlight process
Yes
Upgrade Firmware to Serial Flash U108
by VGA port with ISP_Tool V4.100.exe
Yes
Is R168 open?
Yes
Change R168
Is Q108 work normal?
NO
Yes
Change U105
NO
Is LED at keypad work OK Change LED
NO
Yes
END
END
NO
NO
NO
NO