Samsung LE37A556 Screen Fades to white / Bleaches out

[DemonBG]

Hello Everyone,

My brothers 37" Samsung has recently started acting up and i am wanting some of your wisdom to try and diagnose / fix it.

Background:
I bought the TV about a year ago, faulty. The fault was down to a failed capacitor on the power board. The TV booted up fine but gradually got darker (as though the brightness settings were changing) until the screen was too black to watch (Still could see an image but barely).

The capacitor was not the best quality cap on the market (cannot remember the brand) but was what i had lying around at the time. That was replaced and the TV has been fine until now.

The problem:

The TV boots up fine and the image is good. After about 5 minutes though the screen starts turning white and keeps gradually getting whiter until the screen is almost completely blank after about another minute or two (you can still just about see an image but very faintly).


What i have tried:
I have been told that this sometimes happens due to the boards connected to the LCD panel itself (Not sure what they are called) distort and short. I have followed the advice given here: http://jkturner.net/samsung/ with no joy.

All cabled have been checked over and reseated but again, no joy.


The fact that this happens after a few minutes makes me think it is heat related - possibly the T-Con board?

Will attach pictures as soon as i can.

Thanks in advance,
Demon

[DemonBG]

Re: Samsung LE37A556 Screen Fades to white / Bleaches out

Pictures of the TV doing its thing. First pic is as booted, second is after about 3 minutes, third is after 5 minutes


I dont have any pictures of any of the boards at the moment (May do this weekend) but the T-Con part number:

T-Con Board: T30hw02 v402 37t040c02


Thanks again all,
Demon

[tom66]

Re: Samsung LE37A556 Screen Fades to white / Bleaches out

I would consider heating up parts of the set to try & narrow down the fault.

[DemonBG]

Re: Samsung LE37A556 Screen Fades to white / Bleaches out

Hi Tom,

Ok so i spend the day trying to see if i can narrow the fault down to no avail. It seems the problem was getting worse in the hot weather to the extent that it was white within seconds of turning the screen on - Not enough time to know if the heat had anything to do with it at all...

Either way now i have a fresh problem... In my infinate wisdom and frustration i decided to unplug and replug one of the two cables leading into the LDC panel from the Tcon board while the TV was on. Whatever i did was not a good idea as now i get no image at all on the screen (completely black screen) but i still get sound and the backlight still works.


So... have i killed the set alltogether now or have i likely just fried the T-con board?


Regards,
Demon

[Ken256]

Re: Samsung LE37A556 Screen Fades to white / Bleaches out

Could be something shorted while you were plugging/unplugging the LCD connectors. If you can get it back to its original condition, where the screen would fade to white over minutes, you might be able to diagnose it with a voltmeter. The T-Con board generates or transmits bias and supply voltages. I would suspect some change in the bias voltages over time is causing the fade to white. Put a voltmeter on each voltage rail and see if it changes over time as the symptom worsens.

[DemonBG]

Re: Samsung LE37A556 Screen Fades to white / Bleaches out

Thank you for the reply Ken. I will order a new T-con board if i can find one and see if there is any improvement... For the moment i have a feeling i may have shorted something on the T-Con so will need to replace that first.

Where are the test points on T-con boards though:



Thanks,
Demon

[Ken256]

Re: Samsung LE37A556 Screen Fades to white / Bleaches out

Check fuse F1, next to the input connector. See if it is blown.
I would try probing the test points labeled, VGHC, VGL, VCOM, VCOMF, V12IN1, REF2,3...

[DemonBG]

Re: Samsung LE37A556 Screen Fades to white / Bleaches out

hi Ken,

Thanks for the Input - I checked the fuse in situ when i was there and it was fine.

As i said before im looking to replace the T-Con board. Only problem is i cant seem to find many of the part number i am after: "T370hw02 v402, 37t040c02"

I can find plenty of these though: "37T04COG, T370HW02 VC"

Apart from the mounting points they look fairly similar so i have no idea if it would be compatible or not?


Any advice is always appreciated.

Warm Regards,
Demon

[budm]

Re: Samsung LE37A556 Screen Fades to white / Bleaches out

You have to match the numbers on the BARCODE sticker, the 'T370HW02' is the P/N of the blank board without components.
It looks like it has the same problem with AS15 IC, look under the heat transfering pad on the small IC on the left with square pad to see if it has AS15 number on it.

[tom66]

Re: Samsung LE37A556 Screen Fades to white / Bleaches out

Yes and check VGMA1...VGMA22 voltage, the voltage should increase or decrease from each consecutive point.

[DemonBG]

Re: Samsung LE37A556 Screen Fades to white / Bleaches out

thank you all for the replies. From other posts i am lead to beleive it does have the AS15 chip which i also known is prone to fail...

I will be back with the TV this weekend and will do some more testing and get back to you all.

Thanks again,
Demon

[DemonBG]

Re: Samsung LE37A556 Screen Fades to white / Bleaches out

Update!

So the new T-con board arrived (The number on the barcode was slightly different) but both the numbers on the board itself were the same. Either way, i had nothing to lose so plugged it in and SUCCESS!!

TV booted up without a hitch and no longer fades to white! I am fairly sure it was down to that AS15 chip on the original board but it seems a new Tcon board has saved this one from the skip... at least for a little longer.

One thing i may do is get a stick-on heatsink and place it on the metal shielding directly above the AS15 to try help keep the heat down? Hopefully will save this one from the same fate.


Thanks again all for the help, i really appreciate it!

All the best,
Demon

[budm]

Re: Samsung LE37A556 Screen Fades to white / Bleaches out

Good news, you did transfer the thermal pads from the old board to the new board, right? or the new board does come with all the thermal pads.

[DemonBG]

Re: Samsung LE37A556 Screen Fades to white / Bleaches out

hi Bud,

Yes the new board (Purchased from Flattvparts) was pulled from a used TV so it came with all the pads installed.

Thanks again,
Demon