Dell 1909Wf Service Manual page 36

Service Manual
Power(include IF +5Vand +3.3V) supply normal but LED off and no
display
Is the key function OK?
NO
Is the frequency 14.318MHz at #128 of
IF Board U105?
Yes
Is the low active reset signal at #108 of
IF Board U105 normal?
Yes
Is the serial clock signal at #6 of IF
Board U108 normal when power AC on?
Yes
Upgrade Firmware to Serial Flash U108
by VGA port with ISP_Tool V4.100.exe
END
Power(include IF +5Vand +3.3V) supply and display normal only
LED off
Is the keypad cable connective OK
Yes
Is LED at keypad work OK
Yes
Is R165 open?
NO
Is Q107 work normal?
Yes
Is the LED control signal at 123# of
U105high-low convertible when DC on/off
35
Yes
Press power key to DC on the monitor,if
display ok the process is end,if no
display see the no backlight process
NO
Change crystal X101
NO
Change C164
NO
Yes
Change U105
NO
Change U108
NO Change U105
NO
Reassembly or changing
NO
Change LED
yes
Change R165
NO
Change Q107
NO Change U105