Samsung LE40A656A1F - Possible T-con fault?

[tom66]

Re: Samsung LE40A656A1F - Possible T-con fault?

If it helps you diagnose the problem, I can send you my faulty T-con (with lines, so not a permanent fix, but it is watchable) for the price of postage.

I would suggest you begin testing all LDOs on the T-con.

[senndogg]

Re: Samsung LE40A656A1F - Possible T-con fault?

hello guys and specially tom66.

i didnt want to open a new thread cos the title would be "Samsung LE40A656 - Possible T-con fault?".
well, i have got a LE40A656 with the following symptoms:

Tv switches on/off correctly with the samsung jingle.
switches and functions are ok.
the screen displays the following distortions as shown in the pictures.

done:
re seated the lvds cable. no improvement.
pressed tab bonds. no effect.
recapped, although voltages are still 5,05 the 5,4V rail and 12,89 the 13V rail.
voltage at t-con is 12,4V

i guess it might be a t-con failure or panel, which btw is samsung (presumed good quality).

steps to do next?

[tom66]

Re: Samsung LE40A656A1F - Possible T-con fault?

Thanks, for the feedback. It is always difficult to be 100% sure if it is the main board or the T-CON. Great job!
From SONY: Video Process Failures: All video inputs received by the video process circuits are handled on a frame-by-frame basis. The video frames are converted and scaled to 8 or 10-bit RGB information. It is virtually impossible for the video process circuits to cause a problem on a specific area of the screen. Failures on this board usually appear as distortions, color level shifts, video level shifts or noise that involves the entire picture. The TCON can generate symptoms that appear to be video process related but the video process circuits cannot produce the symptoms of a failed TCON circuit.

The thing that clinched it for me was setting the panel LVDS encoding differently. This made the picture go funky but the noise didn't change. If this option is available this would seem to be a good way of isolating the board at fault.

[budm]

Re: Samsung LE40A656A1F - Possible T-con fault?

Thanks, for the feedback. It is always difficult to be 100% sure if it is the main board or the T-CON. Great job!
From SONY: Video Process Failures: All video inputs received by the video process circuits are handled on a frame-by-frame basis. The video frames are converted and scaled to 8 or 10-bit RGB information. It is virtually impossible for the video process circuits to cause a problem on a specific area of the screen. Failures on this board usually appear as distortions, color level shifts, video level shifts or noise that involves the entire picture. The TCON can generate symptoms that appear to be video process related but the video process circuits cannot produce the symptoms of a failed TCON circuit.

[tom66]

Re: Samsung LE40A656A1F - Possible T-con fault?

YES!!! Another TV fixed .

The 46" board is completely compatible with the 40" - even with the jumpers on the board seemingly indicating different versions.

Got a 32" to fix now and going to the local tip today to have a look for some more.

[tom66]

Re: Samsung LE40A656A1F - Possible T-con fault?

I've ordered the board. I'm going to take the chance that it's compatible. If it's not, I'll just sell it on ebay cheap.

[tom66]

Re: Samsung LE40A656A1F - Possible T-con fault?

Okay, so I went into the service menu and changed the LVDS waveform. Of course, this distorted the picture (colours messed up.) But the noise on the screen stayed the same. This tells me that the noise is likely caused by the T-con. I'll probably take a chance on that T-con. Did factory reset, no dice.

[tom66]

Re: Samsung LE40A656A1F - Possible T-con fault?

I checked the LVDS waveforms with a green signal with noise on it, and no noise appears on the waveforms. This makes me think the noise is coming from the T-con. So I am definitely considering replacing the T-con but I would like input on whether the 46" will work on the 40" model. Anyone know? The board looks identical, but perhaps it has been programmed for a certain screen.

[tom66]

Re: Samsung LE40A656A1F - Possible T-con fault?

Okay, a few tests.

It only affects the green channel. Red and blue are fine.

It can't make pixels "whiter than white", which suggests to me it is digital noise.

Motion Plus doesn't affect it either way.

Pressing on main processors doesn't affect it.

It is evenly spaced, but not related to the position of the four ribbons.

Removing some ribbons doesn't make the problem go away on the rest of the screen.

I attempted to reflow the board with no luck. (Just to see if it would fix it, then I would order a new board.)

The T-con looks identical, except it's for a 46" and it's got extra LVDS connectors (not for panel, and it has the one I need... on my board there are pads for them, but they are not installed.) I think it will be fine for the 40" version though. Budm, have you used mixed size T-cons before, does it usually work?

[tom66]

Re: Samsung LE40A656A1F - Possible T-con fault?

Yes! It does have a Samsung panel.

Okay, when I first got the set, the user remarked the side buttons didn't work, they are some kind of touch sensitive ones. Also I noticed no power LED, which I would usually expect. So, I reseated the connector cable. Result: working buttons, and a power LED. I'm surprised it came loose - it maybe it was not seated properly from the factory. It wouldn't surprise me for Samsung.

The picture is worse with brighter images, but it is definitely digital noise. Not a panel problem, I'm fairly sure. The noise isn't stationary, it flickers and tends to follow objects of certain colours. And it is fixed in those locations. I'm thinking it's a problem with the big heatsinked IC - I suspect this is the 100Hz motion processor, as there's a separate IC which looks like a T-con processor, which is simply attached to the casing of the T-con for a heatsink.

Also, this thing has a friggin' fan? I wondered when I first plugged it in, I heard a grinding noise from the back of the set, so I'm trying to figure out... does it have a HDD? No, it is just a cheap, noisy fan. Any idea on how to fix it? It's not a normal fan - it's got the top of the housing removed so it sucks air through the 100Hz motion processor.

And, I did try the 100Hz motion plus technology. It works okay, but only when things are scrolling or moving in straight lines - otherwise, it doesn't really help motion that much. But it certainly doesn't cure LCD blur, which this TV is more or less immune from, except for certain scenes, but it doesn't look anywhere near as bad as a CMO/Chungwha. The advertising where they show blurry objects is completely wrong: it corrects for jagged movements, from the 25Hz update rate of normal TV, *not* for blur. It doesn't fix LCD blur, it can't - the LCD can only change as fast as it is capable of, and having 100Hz motion plus technology wouldn't improve this either way. Marketing bollocks.

Oh, and the T-con is different to the one linked, so I'll have to find a replacement.

I'm going to scope the LVDS waveforms to check if it's a main board or T-con problem, but I suspect T-con.

[tom66]

Re: Samsung LE40A656A1F - Possible T-con fault?

Like I said in the previous post I remember it looking awesome in HD. It was the first TV that I was really impressed with the watching blue ray and I'd be interested to see who the panel is made by.

The T-con is a Samsung so I hope it's a Samsung panel.

The one thing Samsung do really well is make LCD -panels-. As do LG Display.

It's just a shame the TVs they build them into are absolutely rubbish.

Sadly both Samsung and LG are now using Chi-Mei and Chungwha .

[Jasgriff]

Re: Samsung LE40A656A1F - Possible T-con fault?

Like I said in the previous post I remember it looking awesome in HD. It was the first TV that I was really impressed with the watching blue ray and I'd be interested to see who the panel is made by.

[tom66]

Re: Samsung LE40A656A1F - Possible T-con fault?

Got the TV today.

When I saw the fault, it doesn't seem too bad actually. Definitely still watchable, only faintly noticeable. Definitely doesn't look like panel, it's not on or off, and it flickers. Almost looks like bad SRAM on the T-con or main, the trouble is telling exactly which.

This TV also has USB though not as good as the Samsung plasma I fixed which could play videos. This one can only display JPEGs and play MP3s.

I'll crack it open later... it's still in the car. Big beast, very pretty red frame.

[tom66]

Re: Samsung LE40A656A1F - Possible T-con fault?

Sadly you're most likely going to be dealing with a custom IC, with no datasheet publicly available. The lack of drive almost certainly points to a T-con fault. Scope the crystal oscillator, usually dead if IC is glitchy.

[budm]

Re: Samsung LE40A656A1F - Possible T-con fault?

I check the LDO RT9183-12 (1.2V) check OK.
Another thing is that I did not find any Source/Gate drive for the TFT on the panel itself which is why I do not believe it is bad panel to have that many X/Y drivers to go bad on the whole screen.
I need to look up the spec on that large IC on the T-CON to see how it works.

[tom66]

Re: Samsung LE40A656A1F - Possible T-con fault?

I had a vaguely similar fault with a Samsung; turned out to be a bad LDO on the T-con, one was supposed to give 2.5V but was only giving 1.3V.

[budm]

Re: Samsung LE40A656A1F - Possible T-con fault?

I am working on LG 47LH55 with Horizontal lines and white screen after a minute on top of the pictures, so I did not see bad tab (press on them made no difference) on the panel yet, clean and re-seat the T-CON cable, no luck. There is no active components on the LCD panel board either, check MLC caps for shorts, no luck. I will be ordering new T-CON, TV is only 3 years old.

[Jasgriff]

Re: Samsung LE40A656A1F - Possible T-con fault?

Yeah I am the same a couple are taking up space and gathering dust I need to get them repaired and out of the way.

[tom66]

Re: Samsung LE40A656A1F - Possible T-con fault?

In the video, the noise moves, so I'm hoping it's not a bad panel, as the lines would usually be fixed with a bad panel. Still, I think it might be repairable even with bad tab bonds. I'll see when I get it.

I swear I've seen this problem before, but I'm not sure where! The Sony looks similar, but it's got blocks of fixed colour instead of noise.

I'm getting rid of two of my repaired 32" LCDs this week, so I'm clearing space for a big project...

[tom66]

Re: Samsung LE40A656A1F - Possible T-con fault?

Yep its a shame that company's try to trick customers rather than just making things fair and easy. Its just like the old contrast ratio con.

Pioneer were good at what they did by not advertising the contrast ratio anywhere.

That's probably why they left the TV market. Lie to your customers (and sell them crap at twice the price it's worth) or lose.