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Service Manual
4.Power (include IF +5V and +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 voltage
NO
24V at Q6/Q7
pin3?
Yes
Check U1
pin11
Voltage is 5V
Yes
Check U1 pin2
Voltage is
lower
YES
Check T1/T2 pin7 and pin10 Open
or Short
Yes
Change T1/T2
Yes
Is the on-off control signal #109 of U105
high-low convertible when DC on/off
Check
T850 or
F850
NO
Check
Q7 or
Q6
NO
Is the CN853
inserted CN103 OK?
Yes
NO
Is the frequency 14.318MHz at
#127 of IF Board U105?
Yes
Is the low active reset signal at #105 of
IF Board U105 normal?
Yes
Is the PWM signal at #125 of IF Board
U105 normal when power AC on?
Yes
Update Firmware to Serial Flash U108
by VGA port with ISP_Tool
V4.100.exe,after this process, no the
control signal yet, change U108
33
NO
Change
X101
Change
NO
C164
Change
NO
U105
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