Backlight Can; Acklight Cant Be Turned On - Dell S1909WNf Service Manual

4. Power (include IF +5Vand +3.3V) supply normal, key function OK,but backlight
can't be turned on
Backlight cannot be turned on,is the
on-off control signal come from IF ok?
Yes
Is the
NO
voltage
12V at T1
PIN3/4?
Yes
Check U1
pin1 Voltage
>0.55V
Yes
Check U1 pin8
Voltage is high
YES
Check T1 pin7 and pin10 Open or
Short
Yes
Change T1
Yes Is the on-off control signal #20 of U104
high-low convertible when DC on/off
Check T850,
D854,D855
NO
Check
Q1 or
Q2
NO
Is the CN853
inserted CN103 OK?
Yes
NO
Is the frequency 14.318MHz at #32
of IF Board U104?
Yes
Is the low active reset signal at #19 of
IF Board U104 normal?
Yes
Is the serial clock signal at #6 of IF
Board U105 normal when power AC
Yes
Upgrade Firmware to Serial Flash U105
by VGA port with ISP_Tool
V4.100.exe,after this process,no the
control signal yet,change U104
32
Service Manual
NO
Change
X101
Change
NO
C160
Change
NO
U105