Black mark on LCD Screen.

[JonathanAnon]

I've had this TV for a while.. Fixed the inverter board on it with a temporary fix (cos I couldnt get a new transformer), and gave it to a friend as a loaner.. Was delighted when I managed to track down a new inverter board for it, put it in and it was perfect...... Or I thought it was perfect... :-(

See Video:

http://videobam.com/Hitpb

Seems when it was on loan, it got a belt or something, cos the screen WAS perfect before I lent it out... Now the LCD screen itself seems to be damaged.. I have to throw it out now dont I ....

[truep]

Re: Black mark on LCD Screen.

That looks to be external. Doesn't appear to be cracked. Have you tried cleaning it?

[tom66]

Re: Black mark on LCD Screen.

It's called mura effect. It is either LCD or backlight diffuser problem.

[JonathanAnon]

Re: Black mark on LCD Screen.

It's definitely not external, I was trying to demonstrate this in the window by rubbing the screen, but it didnt come out properly.. It was clearly apparent when I sprayed the screen with cleaner, but this didnt come out well on the video so I didnt include it..

I'm pretty sure it's pressure related as well... as it was fine before being moved in a car..

[tom66]

Re: Black mark on LCD Screen.

If you are prepared to take the LCD apart it may be fixable. Don't dump it anyway with that fault, I have sold ones like that before to people who only want them as second TVs etc.

[JonathanAnon]

Re: Black mark on LCD Screen.

If you are prepared to take the LCD apart it may be fixable. Don't dump it anyway with that fault, I have sold ones like that before to people who only want them as second TVs etc.

Hi Tom, just coming back to this one again.. I dont see how you think it can be fixed

I would have thought that the TFTs or the individual RGB filters in the black areas had been damaged.. The backlight diffuser just diffuses the light from the bulbs, if there was a problem with the diffuser layer, I would have thought that the problem would be a lot more widespread..

[JonathanAnon]

Re: Black mark on LCD Screen.

Sorry double post... My bband disconnected .. :-(

[tom66]

Re: Black mark on LCD Screen.

I have had a TV with mura which turned out to be dirty backlight layers.

[cashkennedy]

Re: Black mark on LCD Screen.

Rather then calling it a "mura effect". Its a pressure spot usually in US when this occurs on a computer monitor.

Apparently tom may be right that these are caused by pressure distorting the sheets between the LCD and the backlight. I used to think it was the pressure mangling the shape of the crystals within each pixel.

If you are careful you don't have much to loose (except for time) to take the set apart and remove the sheets and see if the spot goes away. Perhaps these sheets are intentionally pressure sensitive, so that they can easily be customized to remove the unevenness of backlighting for "quality" sets / monitors where color accuracy matters.

[tom66]

Re: Black mark on LCD Screen.

I'm pretty sure at least 90% of mura is unrepairable.

About 5% of the time the screws on the case can be too tight, applying too much pressure. This is fixed by loosening the screws.

The other 5% of the time, water damage may occur which can cause a similar effect due to backlight layer problems.

[cashkennedy]

Re: Black mark on LCD Screen.

If your right that the pressure spots are from distorting the sheets behind the LCD, which seems quite reasonable to me, then the majority should be fixable by replacing the sheet (not that the sheets are exactly easy to come by)

* as a correction to my previous post , id say rotate the sheets / don't flip them or remove them. That way the part effected will move, but incase the sheet in question is applying the polarity to the light you will get a really bad picture if the sheet is reverse / or removed.

After you know its the sheet, you can try to look for replacements.

[tom66]

Re: Black mark on LCD Screen.

The sheets don't apply any polarisation. That all happens on the LCD panel itself.

[Steve.B]

Re: Black mark on LCD Screen.

Dave on the EEV blog done a tear down of an LCD panel a few weeks ago, contains some interesting information on some of the different layers inside the panel.
https://www.youtube.com/watch?v=kdtyxt9OLlU

[JonathanAnon]

Re: Black mark on LCD Screen.

Dave on the EEV blog done a tear down of an LCD panel a few weeks ago, contains some interesting information on some of the different layers inside the panel.
https://www.youtube.com/watch?v=kdtyxt9OLlU

That's crazy Steve, I actually have Dave's battery tutorial paused on my screen at the moment.. !! I was going through his videos last night and never spotted the LCD tear down, I'll get a look at it. tks.

Dave is great fun.. I remember looking up his soldering video where he says "DONT buy one of those bloody soldering irons that plugs straight in to the wall"... And there I was looking at the three that I had..

[Steve.B]

Re: Black mark on LCD Screen.

Dave is great fun.. I remember looking up his soldering video where he says "DONT buy one of those bloody soldering irons that plugs straight in to the wall"... And there I was looking at the three that I had..

lol, and I've got one of those 'bloody' Vichy multimeters that Dave loves so much. Got to admit though, it is garbage. He makes me laugh when he shows his dislike for something, no holding back!

[tibimakai]

Re: Black mark on LCD Screen.

White pressure marks can be repaired?
I have a dot on one of the TVs.

[tom66]

Re: Black mark on LCD Screen.

Dots, probably not. General smears across the panel maybe.

[JonathanAnon]

Re: Black mark on LCD Screen.

Just digging this one up for an update. Got a chance over the Christmas to open up the TV and take apart the LCD Panel...

Just a quick refresh. The television has a mark on it as in the image below.



So today I took apart the LCD panel and removed the lcd matrix and controllers.


I lay the lcd matrix down on top of my overhead projector and the mark is on the lcd matrix itself.. I've cleaned it but the mark is not going away.


I guess there is nothing more I can do.

[tom66]

Re: Black mark on LCD Screen.

Guess not... who made LCD Panel in this set?

[JonathanAnon]

Re: Black mark on LCD Screen.

Hi Tom,

Here's the tag from the back of the panel.



I'm just wondering what is happening to cause the dark spots. The liquid crystals on those sections must be physically damaged so that they cannot move to the position where they fully allow all light to pass..