Dell E190Sf - Power and Backlight Issues

Service Manual
28
Change U105
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?
Is the CN851
inserted CN101 OK?
NO
Yes
Is the on-off control signal #109 of U105
hi
g
h-low convertible when DC on/off
NO
Yes
Is the
voltage
13Vat T1
PIN3/4
Check
T1
NO
Yes
Yes
Check U1
pin2 Voltage
is 5V
Yes
Check U1 pin6
Voltage is High
Check
CN851
NO
YES
Check U1 pin1 and pin16 Output
Change Q1
Yes
Check
U1
NO