Samsung LN-T4066F Backlight Issue

[aaronwt6]

Trying to repair this set for someone. Symptoms -- Backlight lights for about 1/2 second on power up. Inverter transformer is built in to the power supply however there is an inverter board with a bunch of smaller transformers (balancer I guess). I'll reference this thread for pictures since its the same.

https://www.badcaps.net/forum/showth...ight=ln-t4066f

After the backlight goes off I can clearly see the picture with a light shining on the front. Also, there is 12V going from the PS to the balancer board. All voltages check out.

Anyway, my question is balancer board, PS, or an actual CCFL failure? I of course have no way to test the voltage going from the PS to the balancer. It's labeled at 1500V RMS. I'm thinking the balancer with PS as my 2nd choice but any other opinions would be great.

Thanks as always,

Aaron

[aaronwt6]

Re: Samsung LN-T4066F Backlight Issue

Oh, and if it makes any difference the caps all appear to be in perfect shape. Contrast to the set in the other thread.

[budm]

Re: Samsung LN-T4066F Backlight Issue

There is a small connector with 4pins? ON THE BALANCER BOARD. Can you see the label of those pins like FB, LD, ETC?

[Glitcher]

Re: Samsung LN-T4066F Backlight Issue

Check solder connections where the transformer is on the psu ive had a lot of these models with cracked solder joints there.

If not one check the transformers on the inverter board, one of them may have gone bad. There was a video on how to bypass it somewhere.

Otherwise it might be a burnt out ccfl.

[budm]

Re: Samsung LN-T4066F Backlight Issue

There is video by norcal715 on youtube showing how to look for error voltage on the Balancer board.
http://www.youtube.com/watch?v=oE6K4xBVweA

[aaronwt6]

Re: Samsung LN-T4066F Backlight Issue

Thanks guys. I'll look at the video and check out those solder joints. Here is the connector.

[aaronwt6]

Re: Samsung LN-T4066F Backlight Issue

I have 12.3v on the 12v pin with the TV on and 10.02v on the LD pin.

[aaronwt6]

Re: Samsung LN-T4066F Backlight Issue

Solder looks good on the inverter transformer. There is a buzzing noise on the balancer for the brief moment the lights come on. I thing I may replace that and see what happens. It's only $14. I'll check out that video tomorrow too
and report back.

[budm]

Re: Samsung LN-T4066F Backlight Issue

waiting for the voltage readings tomorrow.

[aaronwt6]

Re: Samsung LN-T4066F Backlight Issue

Ok, so this is strange. I followed the video and all but 3 are around .12V - .145V which makes sense. The other 3 are .38V-.395V and they are right in a row. #2, #3, and #4 looking from the top of the screen down. So, nothing goes up to the point of 1V or more like in the video. And the fact that those 3 are in a row makes me think that it's the board rather than 3 defective tubes that happen to be in a row. All the transformer resistances are within 1% so those look good. I went ahead and order an inverter balancer board so we'll see what happens around Monday.

Thanks again for the help guys,

Aaron

[aaronwt6]

Re: Samsung LN-T4066F Backlight Issue

Update for everyone. There were two issues. Balancer board was indeed bad. Got the new one yesterday. It did not resolve the issue but upon following the video again after swapping the board there was clearly one transformer with too much current draw. I bypassed that one using the instructions from the video and the TV is working now. Can't really even tell the one bulb is out.

Thanks for the help as always guys. Was a new learning experience.

[budm]

Re: Samsung LN-T4066F Backlight Issue

Glad to hear you got it fixed, bad lamp drawing too much current. I think your AC reading is not as high as the one shown on the video is due to your meter does not have the same C frequency bandwidth as the FLUKE he is using (you are trying to measure about 70~80KHz AC voltage). If you look at your voltage ratio between high and low, it is about 1:4.