Samsung BN44-00261B power board backlight inverter fail

[Axxel]

Re: Samsung BN44-00261B power board backlight inverter fail

I'm sorry I moved to mexico and I offered this tv to a freind one year ago... Hope this thread will be helpful to other people

[Apostoliz]

Re: Samsung BN44-00261B power board backlight inverter fail

Hello all! I am bringing back an old post because i have also the same issue with same power board. TV when turns ON backlight stays ON for 2 sec and then turns out but i still have sound. When TV came to me, fuse FI801S was blown due to QI803 and QI804 was shorted. Replaced with 6N90C (cause store hasn't the 5N50) and since then i have that problem. I made a test as i saw in a youtube video, i cut the jumber wire JW154 that connects the SD to the non-inverted input of the comparator UI802/A and tv has backlight again. Is like i force the comparator to has Low BIAS to work but i cant find the source of the problem and i dont want to leave the TV without the current detector protection. Is it possible to have a bad transformer (cause this TV's has this fault often) or a bad lamp? Any advice or help will be appreciated!

[Apostoliz]

Re: Samsung BN44-00261B power board backlight inverter fail

Any idea anyone? I am stuck here!

[misoko]

Re: Samsung BN44-00261B power board backlight inverter fail

Poor transformer is a common problem.

[dick_barton]

Re: Samsung BN44-00261B power board backlight inverter fail

It looks like you have burning top left of transformer. Check the solder joint below and post a picture of the underside of the board where the transformer is located.

[Apostoliz]

Re: Samsung BN44-00261B power board backlight inverter fail

Thank you all for your replies. For the record, transformers are ok, solder joints are also ok. What i did i made is the non inverting input voltage of the UI802/A (lamp over current detector) to have lower voltage than the inverting input. That was done by taking off the jumber wire that connects SD components with the non-inverting input and replacing it with a resistor of 1.8Mohm and with that way i made a voltage divider with the resistor RI865 and drop voltage to apparently 3.2V to non-inverting input. With that way if the voltage increases very much the protector will work also as the voltage will increase and will overcome the reference voltage of the inverted input that is 4.22V of the comparator. So far the TV works fine and the transfomers are warm in normal temperatures. I will leave it to work for a couple of days to see how it goes.

[nomoresonys]

Re: Samsung BN44-00261B power board backlight inverter fail

So you have a faulty lamp??

[Apostoliz]

Re: Samsung BN44-00261B power board backlight inverter fail

The weird thing is that i have downloaded a white fond video from YouTube and i played it to the TV and i dont have any dark spots.....weird i though. Anyways maybe is that you are saying nomoresonys but maybe the lamp has some life. What can i say

[R_J]

Re: Samsung BN44-00261B power board backlight inverter fail

The CCFL are getting weak, they are similar to a florescent tube, If you look at them, the ends will be getting black. and they will be harder to turn on. And it only take one to shut down the power supply, Once it does light up it will be hard to tell in the panel with the other lamps lit up because of the light diffuser sheets.

[Apostoliz]

Re: Samsung BN44-00261B power board backlight inverter fail

So R_J what do you suggest? Because with this situation it is a bit difficult to disassemble the panel and change the tube. You think that i did will last or will blow up the tv eventually?

[R_J]

Re: Samsung BN44-00261B power board backlight inverter fail

The best way would be to replace all the ccfl. I suspect it will last the way it is until one or more of the ccfl totally fails and it will no longer light up at all. It should not blow up anything, but a weak ccfl does put more strain on the inverter as the ccfl takes more current to start up so it might burn up a inverter transformer.

[Apostoliz]

Re: Samsung BN44-00261B power board backlight inverter fail

I believe i understand at the end the source of the problem. I think many questions has been answered. R_J many thanks for your support. I will take that chance with the ccfl. If this TV ends up to me again, i will let you know everyone how long it lasted with this fix. Thanks again and i am appreciated in any help that you provided me!