(SOLVED)Samsung 32" LCD Backlight switches off after 2 seconds

[rythmman]

I replaced the electrolytic caps on the power supply/inverter board, but still get DOUBLE voltage outs ie 10.6vac instead of 5.3vac and 26vac instead of 13vac. Which other faulty components may be causing this?

[downunder]

Can't read the board number, and the voltage legend at top left of picture hard to read, but these voltages are not AC voltages, they're DC, so set your meter to the DC range and try again.

And see what DC voltage appears on the pin designated "BLU-ON'. Expect around 2.5V, supplied by the Main board to turn the backlights on.

Bruce

[rythmman]

Hi, Board number bn44-00369a . The blu-on voltage is 5dcv - double spec, as all the others??
Which component is making ALL voltages double the spec voltage??

[Turnip]

Wonder if you're reading DC voltages from somewhere other than set chassis, say -ve pin of Bridge rectifier as might to check non-isolated voltages ?

Notice BN44-00369A shematic available free on ElektroTanya - Best of luck - Chris.

[rythmman]

Reading -ve DC voltage from chassis screw. Yes, I have the schematic , but still wanted advice on my original question.

[downunder]

Quite the enigma! Doesn't seem quite possible. Main board must be toast by now. Checked your meter?
Can only suggest checking on the secondary side around optos PC801S and PC802S.

I can't discount it entirely, as had the same on an amp last week where a basic bridge rectifier was
outputting twice the listed volts. Never did sort it unfortunately, as so much damage had been done to it, it was no longer worth the effort.

Let us know if and how you correct it..                       Bruce

[rythmman]

I assume, due to the high voltages, that the protection circuit is kicking in and shutting down the backlight?? The LCD is still visible when using a torch.

[Turnip]

Would tend to think that if set is otherwise functioning OK, and as set is fairly modern, that single inverter trannie might have S/C turns - Not unusual, as would cut backlight after seconds.

Just a thought, as can't suss the voltage errors - Chris.

[downunder]

So you say the TV is fully functional except that it's got no backlights. And you can see data on the screen.
Would expect protection would shut the whole set off. Could try unplugging main board from power supply,
turning the set on, and see if the backlights come on and stay on. Would mean the b/lights and power supply are OK and you have a faulty main board. OR

As you get 2 seconds of backlight, why not open the display panel to expose the backlight cavity. Leave anything necessary for the operation of the tv connected. You may unclip the T-con flexies going to the panel and remove the LCD screen and the diffuser sheets under it. Not needed for this test. Switch the tv on and observe the backlights. If any backlight fails to fire, or has a pinkish glow, that'll be your fault. 2 sec is not long, so you may have to repeat the off/on process repeatedly.

[rythmman]

Downunder - I did that and found 1 ccfl tube is pink :) Do I just replace it? Why are the voltages on the PS still high though? Many Thanks

[downunder]

Yes, wise to replace it. Even one pinkisk CCFL can trip the backlight error.

Re PSU voltages, I simply don't know, but what's that cap sticking out sideways in the top of the picture, obscuring the board number?

Bruce

[rythmman]

I couldn't get a 1200 uf cap , so used 2 in parallel...
What do those tubes cost in Aus, I am trying to locate them here?

[Turnip]

Tend to use tubes from screen smash sets, and 32 inch is pretty popular.

Most have wired ends so fitting isn't much of a problem although can vary a bit in length for any screen size.

Best of luck - Chris.

[downunder]

Expect 1200uF in not a preferred value. A 1000uF would have been adequate for the job, but no matter.

Not sure of price or availability (as they are often classed as part and parcel of the panel). I've never changed one in a Sammy. I know that Sharp ones have been available at considerable expense.

There are firms that deal in LCD parts including CCFLs. You could try fleabay or go with Chris's suggestion if you have a wrecked 32" lying about.

Bruce

[rythmman]

Found a good 2nd hand ccfl tube, popped it in and Bob's your Aunty!! So in conclusion, I changed all electrolytic capacitors on PSU/Inverter board and fitted 1 replacement ccfl tube. Thanks to all.