Backlight Can; Acklight Cant Be Turned On - Dell E190Sf 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
13Vat T1
PIN3/4
Yes
Check U1
pin2 Voltage
is 5V
Yes
Check U1 pin6
Voltage is High
YES
Check U1 pin1 and pin16 Output
Yes
Change Q1
Yes Is the on-off control signal #109 of U105
high-low convertible when DC on/off
Check
T1
NO
Check
CN851
NO
NO
Is the CN851
inserted CN101 OK?
Yes
NO
Change U105
Check
U1
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Service Manual