Samsung BN44-00284A Backlight problem

[sandinemail@hotmail.com]

Samsung BN44-00284A in a Samsung LE40B755 TV bought 2009.

In November 2020 the TV didn´t turn on only flashing red diod on front off TV.

I then opened up the TV and found bulged capacitors on the inverter/powerboard.

I changed all capacitors except the main two 450V 100uf capacitors.
The TV has worked pefectly since.

But this week it started to turn off the backlight. Audio on TV still works.
Sometimes it turn off the backlight after 10 seconds but sometimes it works for hours.

Any suggestions on what might be wrong and how to fix it?

[nomoresonys]

Re: Samsung BN44-00284A Backlight problem

check over all solder joints, specially those components on heatsinks, and the transformer legs, reflow any that look suspect, careful not to bride any joints that shouldn't be with solder and recheck your solder work on caps, one might have been not too good, Another test, maybe when it's acting up heat up your electrolytic caps with a hairdryer for a couple minutes, see if it comes on any better, if only for a bit.

[sandinemail@hotmail.com]

Re: Samsung BN44-00284A Backlight problem

Have already resoldered all transformer and mosfet legs.

[sandinemail@hotmail.com]

Re: Samsung BN44-00284A Backlight problem

If I turn up backlight settings to 10 it immediately turns off backlight.

[nomoresonys]

Re: Samsung BN44-00284A Backlight problem

what does it do with them turned way down?

[sandinemail@hotmail.com]

Re: Samsung BN44-00284A Backlight problem

Sometimes it works for a couple of hours sometimes for a couple of minutes.

[nomoresonys]

Re: Samsung BN44-00284A Backlight problem

I might suspect one of the backlight transformers or possibly bad ccfl or connection in that circuit.

[sandinemail@hotmail.com]

Re: Samsung BN44-00284A Backlight problem

Ok
Not main capacitors 450V 100uf?

Couldn’t find any schematics of the inverter/powerboard.

[vinceroger69]

Re: Samsung BN44-00284A Backlight problem

my guess is a failing ccfl tube

[nomoresonys]

Re: Samsung BN44-00284A Backlight problem

maybe ohm check those transformers, they should be very close to each other in reading.

[nomoresonys]

Re: Samsung BN44-00284A Backlight problem

well it could be those big caps, you have a way to test them? can ohm test them, dirty test is put meter on 20k ohm or maybe higher and test them, they should go up or down steady, reverse probes should be steady climb or decrease, not terribly accurate test but can give a clue at times.

[sandinemail@hotmail.com]

Re: Samsung BN44-00284A Backlight problem

Resolder the caps first?

[nomoresonys]

Re: Samsung BN44-00284A Backlight problem

ohm testing done with tv UNPLUGGED from power, for those looking on that might not know.

[sandinemail@hotmail.com]

Re: Samsung BN44-00284A Backlight problem

How to test ccfl tube?

[nomoresonys]

Re: Samsung BN44-00284A Backlight problem

Resolder the caps first?

sure, if they look bad or suspect.

[nomoresonys]

Re: Samsung BN44-00284A Backlight problem

the ohm test is easy enough, done with caps in place, no need to take out for that.

[sandinemail@hotmail.com]

Re: Samsung BN44-00284A Backlight problem

Measured with 6Mohm on multimeter.
Goes up steady. Reverse goes down slowly.

Capacitor measurement shows 190uf

[nomoresonys]

Re: Samsung BN44-00284A Backlight problem

could be similar to this problem: https://www.youtube.com/watch?v=PflyJ4H51Fg

[nomoresonys]

Re: Samsung BN44-00284A Backlight problem

so thats probably the total uf of both then.

[nomoresonys]

Re: Samsung BN44-00284A Backlight problem

.