Backlight Can't Be Turned On - Samsung 720N Service Manual

4-5 Backlight can't be turned on

No backlight
Yes
LED lamp is OK
Yes
Is there 14V
voltage on pin 3,4
of T501, T502
Yes
Is there PWM
signal on pin 4 of
IC501
Yes
Is there High level
voltage on pin4 of
IC501
Yes
Vsense voltage
2.9V
No
Are there PWM
signal on pin1,
pin15 of IC501
Yes
Pin 5 of IC501
voltage is Low level
Yes
Pin 5 of IC501
voltage is high level
voltage
END
No
No power supply to
inverter
No
U501, U502 fail
No
Check I/F BD
No
Check I/F BD
No
Lamp connector opened
No
IC501 failure
Yes
Feedback circuit failure
Yes
IC501 protected
4 Troubleshooting
Yes
Check the cable that from
I/F BD to P/I BD is ok
No
Check power supply
Replace U501, U502
Yes
Check R523, D504,
R529, D507, R528, R533
Yes
Check D505, D506,
D510, R522, R521, C520
4-5