Samsung LE46C750 TV, dead but backlight on.

[Andy A]

I have a Samsung LE46C750 TV

There are no LED'S lit on the front panel of the TV when powered up.

When powered is supplied to the TV the backlight comes on, no sound and no picture.

I cannot see any sign of damage to any of the components on the main logic board (BN41-0142 B) or the power supply board (BN44-00341A)
I have tested the voltages from the power board to the main logic board and all voltages are correct except one.





Pin 18 PS_ON reads 0.8V I linked from pin 16 a 5V pin to pin 18 PS_ON using a 1K resister and the voltage only went up to 1.6V. I pulled the pin from the connector PSU end and tested the voltage again on pin 18 going back to the main logic board and got 4.6v that dropped to 4.3v after a short time. When the pin is plugged back into the connector it drops tp 1.6V again.

None of this made any difference unfortunately.

Any one got any ideas on what can be causing this?

Thanks

[nomoresonys]

Re: Samsung LE46C750 TV, dead but backlight on.

Always start with pictures of ALL the boards and one of the whole back, it makes things much easier to solve, because there's a lot of different configurations on tvs.

[Andy A]

Re: Samsung LE46C750 TV, dead but backlight on.

Very good advice. Here are some more pics.











Hope this helps.

Thanks

[dskall]

Re: Samsung LE46C750 TV, dead but backlight on.

I would say a mainboard issue. You could try heating main chip and see if that changes anything, but unless you are experienced with testing voltages and know if they are correct. I would say replace mainboard.

[Andy A]

Re: Samsung LE46C750 TV, dead but backlight on.

[QUOTE=dskall;1109839]I would say a mainboard issue. You could try heating main chip and see if that changes anything, but unless you are experienced with testing voltages and know if they are correct. I would say replace mainboard.

Is the main chip under the black heatsink that is just below the silver one?

What is the heatsink stuck on with?

If yes I will get the heat gun on it tomorrow.

[nomoresonys]

Re: Samsung LE46C750 TV, dead but backlight on.

Another test, unhook the cable from mainboard to tcon board, see if that ps on voltage changes from what you have.

[Andy A]

Re: Samsung LE46C750 TV, dead but backlight on.

Another test, unhook the cable from mainboard to tcon board, see if that ps on voltage changes from what you have.

The voltage stayed the same 0.8V.

[Diah]

Re: Samsung LE46C750 TV, dead but backlight on.

1- disconnect the main boards socket which come from power boards... plug in wall see if the backlight lit on strong enough to notice them.

if no or weak... i remember the shape of this power boards... its much had crack soldering or fault caps.

[nomoresonys]

Re: Samsung LE46C750 TV, dead but backlight on.

good idea Diah, check the solder joints, look below.

[Andy A]

Re: Samsung LE46C750 TV, dead but backlight on.

1- disconnect the main boards socket which come from power boards... plug in wall see if the backlight lit on strong enough to notice them.

if no or weak... i remember the shape of this power boards... its much had crack soldering or fault caps.

Disconnected power board and backlight is nice and bright.

I will take out the power board tomorrow when the lighting is better in here and have a good look around for any dry/cracked solder joints.

All the caps look fine.

Is this all pointing back to a power board problem and not a main board problem?

[vinceroger69]

Re: Samsung LE46C750 TV, dead but backlight on.

on the tcon board you will see a fuse thats usually by the lvds cable connector check you have 12v to both sides of the fuse.

[Andy A]

Re: Samsung LE46C750 TV, dead but backlight on.

on the tcon board you will see a fuse thats usually by the lvds cable connector check you have 12v to both sides of the fuse.

Just checked. There are 2 fuses side by side and 12v is present on both sides on both fuses.

[nomoresonys]

Re: Samsung LE46C750 TV, dead but backlight on.

seems like something on the mainboard is wrong/bad and dragging down the ps-on voltage.

[Diah]

Re: Samsung LE46C750 TV, dead but backlight on.

Just checked. There are 2 fuses side by side and 12v is present on both sides on both fuses.

how about if you disconnect one side at time ribbon cable between T-CON and panel did you got half screen white?

EDIT:

so yours V. check at First post had error.. your PS ON fine and PCB fine that 12V exsist on T-CON. and i think when you turn on your optical audio port lit red color !!!

[Andy A]

Re: Samsung LE46C750 TV, dead but backlight on.

Just tried that and it made no difference.

[vinceroger69]

Re: Samsung LE46C750 TV, dead but backlight on.

mainboard fault would be my guess but a quick look on ebay i cant see any available so maybe a common issue

[Andy A]

Re: Samsung LE46C750 TV, dead but backlight on.

mainboard fault would be my guess but a quick look on ebay i cant see any available so maybe a common issue

Might of found a replacement main board. Just waiting for a reply from them.

The chip that needs heating up on my old board to try and reflow. Is it the one with the metal case over the top?

Just taken the heatsink off very easy, because all the adhesive was dried up solid. I do have a hot air station.

[vinceroger69]

Re: Samsung LE46C750 TV, dead but backlight on.

Might of found one. The chip that needs heating to try and re-ball. Is it the one with the metal case over the top?

Just taken the heatsink off very easy, because all the adhesive was dried up solid. I do have a hot air station.

I have never re flowed one of these boads so not sure which ic maybe at fault hopefully a more experienced member will know and advise

[Andy A]

Re: Samsung LE46C750 TV, dead but backlight on.

I have never re flowed one of these boads so not sure which ic maybe at fault hopefully a more experienced member will know and advise

Hopefully some one can shed some light

I think it might be the DNIE IC7001. I read that it controls video but I'm not sure if it controls the sound and the problems with no LED's on the front of the TV.

[dskall]

Re: Samsung LE46C750 TV, dead but backlight on.

I am only suggesting heating up main chip and see if anything changes. Trying to confirm where problem might be. But the logical step here is to confirm voltages on mainboard.