Dell E1909W - Power(include IF +5 Vand +3.3 V) supply normal but LED off and no display

Service Manual
31
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
#127,#128 of IF Board U105?
Change crystal X101
NO
Yes
Is the low active reset signal at #108 of
IF Board U105 normal?
NO
Change C164
Yes
Is the PWM signal at #125 of IF Board
U105 normal when power AC on?
NO
Change U105
Yes
Change U105
NO
Is the keypad cable connective OK
Reassembly or changing
Yes
Is theLED control signal at 123# of U105
high-low convertible when DC on/off
NO
NO
Change Q107
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 R165 open?
yes
Change R165
Is Q107 work normal?
NO
Yes
Change U105
NO
Is LED at keypad work OK
Change LED
NO
Yes
END
END