Checking The Back Light Unit - HP WF1907 Service Manual

4.3 Checking the back light unit

Is +20V supplied to inverter PWB ? (by the
power board)
OK
Check the BACKLIGHT_EN signal of the
P301 pin 2 at high level.
OK
Check the BACKLIGHT_ADJ signal of the
P302 pin 3 from I306 pin 50 is a PWM
signal.
OK
Failure Point
Back light unit of LCD module is failure.
Failure Point
NG
1) Inverter cable disconnection.
2) Power board failure.
Failure Point
NG
1) printed wire broke between P301 pin 2,
R305 and I306 pin 49.
2) R305 is open, or R306, C308 are short.
3) I306 is failure.
Failure Point
NG
1) printed wire broke between P301 pin 3,
Q301 and I306 pin 50.
2) Q301 is failure.
3) R301 or R302 or R304 is open, or C304
is short.
4) I306 is failure.
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