Samsung 720N - Backlight Cant be Turned on

4 Troubleshooting
4-5
4-5 Backlight can't be turned on
LED lamp is OK
No backlight
No power supply to
inverter
Check the cable that from
I/F BD to P/I BD is ok
Check power supply
Replace U501, U502
Yes
Is there 14V
voltage on pin 3,4
of T501, T502
U501, U502 fail
Yes
Yes
No
Is there PWM
signal on pin 4 of
IC501
Check I/F BD
No
Yes
Is there High level
voltage on pin4 of
IC501
Check I/F BD
No
Yes
Vsense voltage
2.9V
Lamp connector opened
No
No
Are there PWM
signal on pin1,
pin15 of IC501
IC501 failure
No
Yes
Pin 5 of IC501
voltage is Low level
Feedback circuit failure
Yes
Check R523, D504,
R529, D507, R528, R533
Yes
Yes
Pin 5 of IC501
voltage is high level
voltage
IC501 protected
END
Yes
Check D505, D506,
D510, R522, R521, C520
Yes
No
Yes
No