Samsung 40inch lcd tv backlight goes off sound good

[shelby5041]

Model lns4051dx/xaa

tv powers on fine and picture is great but after a random amount of time while watching tv the backlight will go off and the sound stays on

this can be 5 minutes 10 minutes 30 minutes 1 hr ...2hrs etc...it varies from day to day....

I have tested the output voltages on the cables from ps and they all check good...there seems to be 2 inverter boards and i get 12v going to both from the lower power cable....but there is a transformer with 2 wires going to top of i assume the master inverter and not sure how to check for voltages there...nothing marked...one wire is blue and one is white....its marked with ????? On photo

any ideas what the problem could be? Inverter bad? Backlight bad?..if it is a bad inverter how can i tell if its master or slave inverter..

Thanks

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

Here are photos

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

forgot to mention when the backlight does go off i get good voltages coming from ps.....just not sure how to check the blue and white wires from what appears to be a transformer on ps to master inverter.........

[nomoresonys]

Re: Samsung 40inch lcd tv backlight goes off sound good

not sure, but just read some of those transformers can carry 2000 volts, enough to fry a multimeter and kill a man.

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

yes.....but shouldnt i be able to test the output power via the blue white wires coming out of transformer going to master inverter?

[nomoresonys]

Re: Samsung 40inch lcd tv backlight goes off sound good

not sure about your particular setup, if you can or not.

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

nope there is nothing on the board at all...just the blue and white wire coming out from trans going to master inverter.....

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

ok well maybe someone can answer this..what is the purpose of two power lines going to inverter...the 12v on bottom and the wires coming from trans on top?

[nomoresonys]

Re: Samsung 40inch lcd tv backlight goes off sound good

wrong post.

[nomoresonys]

Re: Samsung 40inch lcd tv backlight goes off sound good

just noticed, this is the exact model Im working on.

[nomoresonys]

Re: Samsung 40inch lcd tv backlight goes off sound good

see the other wire going to the inverter? it should say 12 v on legend, you can check that.

[nomoresonys]

Re: Samsung 40inch lcd tv backlight goes off sound good

this is the one I cant find a manual for, maybe I can find one thats close.

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

yes if you read my post and look at my pic it says i got 12v from that cable

[nomoresonys]

Re: Samsung 40inch lcd tv backlight goes off sound good

check these, http://www.toms-service-manuals.com/...h=Submit+Query

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

i get good voltages on all wires from power supply other than not checking the wires coming from large transformer

[budm]

Re: Samsung 40inch lcd tv backlight goes off sound good

Those two long boards connected to the lamps are the Balancer boards, the 12V is normal, bad< = 10VDC.
Try disconnecting the cable between the main board and the power supply/inverter board combo and see if the backlights will come on and stays on the minute you plug the power cord into the outets.
Do not touch or try to measure the high voltage from the power supply/inverter board high voltage out put or you will blow up your meter.
What is the P/N of that power supply/inverter board? BN44-??????

[nomoresonys]

Re: Samsung 40inch lcd tv backlight goes off sound good

we need a repair or training manual for this model, havent been able to find one.

[nomoresonys]

Re: Samsung 40inch lcd tv backlight goes off sound good

Those two long boards connected to the lamps are the Balancer boards, the 12V is normal, bad< = 10VDC.
Try disconnecting the cable between the main board and the power supply/inverter board combo and see if the backlights will come on and stays on the minute you plug the power cord into the outets.
Do not touch or try to measure the high voltage from the power supply/inverter board high voltage out put or you will blow up your meter.
What is the P/N of that power supply/inverter board? BN44-??????

mine is bn44-00134a.

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

thanks budm....ok so the two long boards are not typical inverter boards?....yes i do get 12v coming from ps as shwon in my photo......so you want me to disconnect the power supply connection to the main/input board? and then fire up the tv?....the tv shouldnt power up....that has all the voltages on it....correct?

note: i saw a youtube video where a few people had exact same tv and the treansformer had bad solders which would cause intermittent backlight issues....just like mine...

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

the pn is in one of my photos.posted ill check now..