Fault with Samsung LE37A656A1FXXU

[markhambly]

I have Samsung le37a656a1fxxu, reasonably old LCD TV. The colours on the screen started to go a little while ago, and now has gone completely white.
If starting from cold, the picture is fine for a very short time then goes white, firstly like a washed-out negative picture then completely bright white.
The audio comes through clear throughout.
I took the back off and there were 2 25V 1000uF capacitors which are slightly bulging on the power supply board. There is a black spot on each of the capacitors which I thought was electrolyte but actually looks more like paint or ink, because it's even on the ones which are flat-topped. I replaced them anyway and tried again. No change, just new capacitors!
Any ideas where the fault may lie? I have read a lot about the TCON boards failing, so I have removed it ready to replace, but it now seem more sensible if I had left it in for testing.
I read a similar thread earlier today, which recommended testing VGAMA voltages. Can you test these points with the board connected only by the board-board connectors (without the screen ribbons - this is out of laziness because they're harder to get at), and should the voltages gradually ramp up/down as in the previous post case?
I am a reasonable technical person with background in science and engineering degree, but I have never fixed a TV! I have already replaced the TV so I am happy to have a go at fixing it with some guidance.
Can anyone help?
Mark

[newtothis]

Re: Fault with Samsung LE37A656A1FXXU

Pics of each board individually, one of entire back of chassis and close up of connectors so we can read any silk print.

[markhambly]

Re: Fault with Samsung LE37A656A1FXXU

Thanks for speedy response. Here is one of the TCON, but I'll get the others ASAP, may not be until Tue though as work rather inconveniently gets in my way!
I'll get the VGAMA voltages when I have the back off.

[markhambly]

Re: Fault with Samsung LE37A656A1FXXU

Sorry about the dreadful quality photo - I'll redo that too if needed. The VGAMAs are in the top right, 1-14.

[budm]

Re: Fault with Samsung LE37A656A1FXXU

The IC on the top right of the board is the Gamma Voltage ref IC, can you remove the thermal transfer pad and see if it has AS15 printed on top?
AUOPTO tends to have the bad AS15 Gamma IC.

[markhambly]

Re: Fault with Samsung LE37A656A1FXXU

The chip is AS15. What's my next move, check the voltages at the VGAMA points? Swap the board?
If there's any way to check it that would be preferable to buying a new one just to see.

I haven't forgotten about the request for photos - will be able to get onto that tomorrow.

Mark

[DLinkOZ]

Re: Fault with Samsung LE37A656A1FXXU

Trying to help out, considering the immense help I've received here. If you scroll towards the bottom of my post:

https://www.badcaps.net/forum/showthread.php?t=33405

You'll see some discussions about identifying that AS15 chip as bad via measuring the gamma voltages. What mine look like (bad) and what they should look like.

[budm]

Re: Fault with Samsung LE37A656A1FXXU

Replace the IC, you will need SMD hotair work station or replace the board.

[markhambly]

Re: Fault with Samsung LE37A656A1FXXU

Looks a bit challenging to change the IC with no experience, but might give it a to as nothing to lose. Better check the voltages first though.
Can anyone point me in direction of good advice re best way to change the chip?

[markhambly]

Re: Fault with Samsung LE37A656A1FXXU

Oh, and thanks so much for the link dlinkOZ and the advice budm, very helpful.

[DLinkOZ]

Re: Fault with Samsung LE37A656A1FXXU

I have the experience, but not the hardware currently to change that IC. Since I'm only 20 minutes from Coppell, I'm going to use their $50 service to get it swapped out properly.

[newtothis]

Re: Fault with Samsung LE37A656A1FXXU

Can anyone point me in direction of good advice re best way to change the chip?

In the case of using hot air :

Hot Air SMD Station
Good Soldering Iron
Flux (I use Amtech)
Solder
Solder Wick
IPA (99% or above) (or use lint free IPA rubs)
Fine pitch soldering tip (in case of bridging or touch ups)
Lint free cloths (not need if using rubs)
ESD Safe tweezers

In the case of soldering iron only :

Good soldering iron with interchangeable tips
flux
Low melt solder
solder
solder wick
IPA (or same as above)
ESD Safe tweezers

If you don't have the equipment it will usually cost more to do a single repair... if you are going to use the equipment a lot its worth it. Good flux is expensive and has a use by date so if your not going to use it its a waste.

I could go into the methods if you want too... but no point me writing it if you aren't going to do the repair yourself

[markhambly]

Re: Fault with Samsung LE37A656A1FXXU

Thanks for the offer newtothis, I'll check out the voltages and see what I'll do. The boards seem to be available for 60 odd pounds so may not be worth it. However, I do like a challenge so may give it a go, as the board's trash anyhow.
I'll get back to you.

[markhambly]

Re: Fault with Samsung LE37A656A1FXXU

Just reconnected the board - voltages all over the place. I only connected it by the board-board leads and din not bother with the ribbons - will that affect the readings. Th reason I did not connect them is that the cables are glued to the metal cover which means if I connect them access to the board is severely restricted for testing.
VOltages:
1 - 6.84
2 - 12.16
3 - 7.28
4 - 0.04
5 - 7.04
6 - 7.29
7 - 7.29
8 - 6.51
9 - 6.43
10 - 4.74
11 - 4.48
12 - 3.93
13 - 0.31
14 - 0.21

[markhambly]

Re: Fault with Samsung LE37A656A1FXXU

Just a quick note to say that I ordered a new board on ebay and now TV works perfectly.
Thanks for all the advice guys.

[tom66]

Re: Fault with Samsung LE37A656A1FXXU

As a note for future users yes those voltages are very bad, and you can leave the connectors disconnected. Thanks for repair feedback.