Dell E1709W - Backlight Cannot Be Turned On

Service Manual
32
Is the frequency 14.318MHz at #2
of IF Board U105?
NO
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?
Is the CN851
inserted CN101 OK?
NO
Yes
Is the on-off control signal #55 of U105
hi
g
h-low convertible when DC on/off
NO
Yes
Is the low active reset signal at #54 of
IF Board U105 normal?
NO
Change
C164
Yes
Is the serial clock signal at #6 of IF
Board U105 normal when power AC
Change
U105
NO
Upgrade Firmware to Serial Flash U105
by VGA port with ISP_Tool V4.100.exe,
after this process,no the control signal
yet,change U105
Yes
Change
X101
Yes
Is the
voltage
12V at T1
PIN4?
Check
T850,
D801
NO
Yes
Yes
Check U1
pin4 Voltage
is 2V
Yes
Check U1 pin8
Voltage is high
Check
U2
NO
YES
Check T1 pin7 and pin10 Open or
Short
Change T1
Yes