Samsung LN46D630M3F, TV powers on, sound works but no backlight

[dick_barton]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

Have you measured the primary and secondary sides of the inverter transformers to check that they all have identical readings?

[Five_magics]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

QI802 and QI808 are okay (at least, not shorted). FS802S is good.

Tested CI818's ESR which was fine, gonna check the capacitance tomorrow.

[budm]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

CM801 is part of the main power supply and you are getting the 12V, etc. so that will not be the problem.
You have power supply-inverter transformers driver board (QI802, QI808 are the power MOSFETs for driving the inverter transformers (3) board).
Fuse FS802S for supplying the B+ to the Inverter driver circuit is OK?
You also need to check the cap CI818 (0.47uF) to make sure the capacitance is still within 10%.

[Five_magics]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

Here are pictures of the main board, power supply and inverter board.

Took the power supply to work today to test the ESR of caps. Turns out one of the electrolytic I put in is bad (30 ohms+). Also CM801 gives no reading, wondering if that could have to do with the value? I usually measure capacitors above 1uF. You can also clearly see heat marks near it.

[CapLeaker]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

probably the inverter board.

[Five_magics]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

Like I said, with everything plugged in the backlight(CCFL) doesn't even light up. When the main board is disconnected, it lights up for half a second and shuts off.

Will take pictures and post tomorrow.

EDIT: Missed the stickied thread. Sorries!

[RCA2000]

Re: Samsung LN46D630M3F, TV powers on, sound works but no backlight

USUALLY...a BL that "lights for a couple of seconds and then drops...is the fault of the BACKLIGHTS--be they CCFL tubes of LED"S.

Show a rear pix of panel with all boards--and I will get a better idea of things to go on...

[Five_magics]

Hey! So I have this LCD TV (Samsung LN46D630M3F) which is my brother's and needs to be fixed, been out of the troubleshooting world for a while, thought I'd ask here. The set is 5 years old or so.

Basicly, the TV powers on, plays some Samsung tune, and isn't backlit(not even for a second). From what I got told, the TV worked just fine one night, and the next morning it didn't.

Already ordered an inverter board on a whim, until then I'm trying to see if the power supply isn't at fault. Already swapped all electrolytic capacitors, also checked most semi-conductors and they all seem fine (at least none are shorted). When everything's plugged in and TV is powered on, there's a coil whine coming from the power supply unit for half a second then it stops.

Took some voltage readings at the inverter's connector tonight, which are;

LD=10,8v
13v=12,1
CNT_PRT (current protection?)=11,6v
OVP=0v
GND=0v

Also tried powering up the set without the main board connected; backlight lights up for half a second and shuts down. Tried taking readings at the inverter connector with the main board/inverter disconnected, but forgot to take notes. Will do it again tomorrow. Didn't bother taking primary readings at this point.

After a google search, couldn't find the power supply schematic (BN44-00463A), so if anyone has it, that'd help a ton.

Any help is welcome. Thanks!