Samsung 32" LNS3238DX/XAA LCD pixelated

[cliff_hootarski]

Hi again everyone,

I've acquired another broken display. The display is pixelated in all display modes. I'm trying to ascertain whether the problem is the Tcon board or
the main signal board, or perhaps a bad LCD. Wiggling the LVDS wires from the main board to the Tcon board does not change the display. (A Tcon
board on Ebay can be had for as little as $10).

I've attached pictures of the picture displayed and the internals of the TV.

Thanks for any help,

Jerry

[PlainBill]

Re: Samsung 32" LNS3238DX/XAA LCD pixelated

That certainly looks like AC ripple. My first move would be to check the power supply, in particular the voltage across the large Capxon cap while the TV is working. My second would be to seriously consider a complete recap of the power supply.

PlainBill

[cliff_hootarski]

Re: Samsung 32" LNS3238DX/XAA LCD pixelated

That what I like about this site. I had not thought about AC ripple.
Will a digital DMM work for that or will I need and O-scope?

Jerry

[tom66]

Re: Samsung 32" LNS3238DX/XAA LCD pixelated

You will most likely need a scope. You may be able to get away with earphones.

Another option is the T-con is failing. The lines look almost like digital noise, like from a noisy LDO that has nearly failed. If the T-con is cheap I would give it a go before looking to other things.

[cliff_hootarski]

Re: Samsung 32" LNS3238DX/XAA LCD pixelated

Measured 384v DC/1.12v AC across the large Cap.
Ordered a Tcon from Ebay this morning.
Could you explain the "earphone" method for checking ripple?

Thanks,

Jerry

[tom66]

Re: Samsung 32" LNS3238DX/XAA LCD pixelated

Do you have a 100uF capacitor and a set of headphones you don't mind potentially damaging?

[cliff_hootarski]

Re: Samsung 32" LNS3238DX/XAA LCD pixelated

I'm fairly sure I could dig those up somewhere.

Jerry

[tom66]

Re: Samsung 32" LNS3238DX/XAA LCD pixelated

Put the capacitor in series with the headphones. Connect the cap positive end to the voltage you want to probe, and negative to the left or right of the headphones. The ground goes to the ground of the TV. If you are trying to measure a negative voltage, reverse the capacitor. Note: The capacitor should be rated for at least 20% more than the supply voltage you are trying to measure. e.g. use a 35V cap for 24V. And do not attempt to measure the ripple across the main cap doing this, you could easily electrocute yourself and destroy the headphones.

You should hear a very faint noise if the PSU is working correctly. If it sounds like a loud hash then something is wrong...

This was used by radio technicians yonks ago - the proper way to do it is to get a scope - but it can be used to do a spot check. The problem is, it's very subjective. And it's very dependent on the headphones and your hearing. Also, some of the higher frequencies, despite being ripple, can be inaudible.

[cliff_hootarski]

Re: Samsung 32" LNS3238DX/XAA LCD pixelated

I replaced the Hot side main filter Cap (150microfarad/450v) with another cap from another power supply. Still the same picture.

[cliff_hootarski]

Re: Samsung 32" LNS3238DX/XAA LCD pixelated

I also removed the secondary filter caps and measured with
Atlas ESR70, replaced two caps(marginal esr) with tested good caps and still no change in the display.

I'll wait for the ordered Tcon board to get here to see if that fixes it.

[cliff_hootarski]

Re: Samsung 32" LNS3238DX/XAA LCD pixelated

Got the Tcon board in yesterday and installed it. No change. Looks like a main board problem.

[cliff_hootarski]

Re: Samsung 32" LNS3238DX/XAA LCD pixelated

Finally found a main board @ shopjimmy. Installed and works like a champ now!

[tom66]

Re: Samsung 32" LNS3238DX/XAA LCD pixelated

Finally found a main board @ shopjimmy. Installed and works like a champ now!

Great to hear. Thanks for posting your fix.

[budm]

Re: Samsung 32" LNS3238DX/XAA LCD pixelated

Try figure out if the problem is with T-CON or Main board is always hard to be 100% for sure, this symptom and the fix will go into my library. I would have bought the T-CON board also since it is cheaper than the main board, and if it does not fix it then I will figure out if it will be worth to buy the new main board. Thanks for sharing.