1. Home
  2. Electronics Repair
  3. More strange LCD distortion ...

More strange LCD distortion ...

Following on from my slightly OT post of a few weeks ago regarding the 'impossible' H linearity error that I saw on the Delta in-flight LCD screen, tonight, I saw another. This time it was on an LCD screen at my local bingo hall. I would guess that it's about a 22", standard 4:3 aspect ratio. Used to display numbers when they are playing tabletop cash bingo, and winning cards during normally called bingo. There are many screens around this large hall, all being fed from the same primary video source, so I think that incoming signal can be eliminated.

This one had a 'foldover' of about 1.5" at the top left corner. It progressed across the screen getting less and less, until at the right hand side, the top of the picture was absolutely normal. The 'foldover' was extremely non linear. It looked to be very stretched, to the point where you could see what you would describe as individual scanning or field flyback lines - if it were a CRT display ...

I thought I was reasonably au fait with the way an LCD screen was driven from its frame buffer, but I'll be buggered if I can see a way that data could be read out erroneously, in such a way as to produce a badly stretched tapering wedge of foldover, across the top of the screen. Anyone seen anything like *this* one, or have any suggestions how it could occur ... ??

Arfa

Reply to
Arfa Daily
Loading thread data ...

The screens are probably being fed an analog signal. Some noise or electronics failure is causing it to improperly sync.

--
If there is a no_junk in my address, please REMOVE it before replying!
All junk mail senders will be prosecuted to the fullest extent of the 
law!!
http://home.att.net/~andyross
Reply to
Andrew Rossmann

Imaginary ...

These are old unspent CRT nightmares from an age ago, Arfa, that you must have been dreaming about with such realism whilst asleep. Except your mind has updated the display technology to LCD.

Too much wine? Long flight? Exciting Bingo session?

Need to see a declaration that 'ye pinched yourself' while noticing the effects.

;-)

--
Adrian C
Reply to
Adrian C

Its as if the signal was distorted before it ever got to the LCD. Isn't that possible?

Reply to
Meat Plow

Hi Adrian

Nope. Yes. Nope !

No wine on either the flight or at bingo, Yes, it was a long flight, but that just gave me plenty of time to study the problem on that one (and reach no conclusions). No - not a very exciting bingo session. I didn't even want to go, but saying no to the missus when she's decided that is where we are going - well, work out the consequences for yourself !

However, on a more serious note, the problem observed on this particular monitor, was quite real. It is a ceiling suspended monitor, and definitely LCD. For sure, it is being fed with an analogue signal, but so are the other probably thirty similar monitors distributed throughout the club, and they all carry the same content at the same time, as I think I said at the beginning, and no other that I saw was exhibiting the same problem, which pretty much eliminates the content of the feed. Even if it was a problem with the signal, I can't for the life of me think what that problem could be, to cause that symptom. And not any kind of sync issue that I can think of either. The picture was perfectly stable in both the H and V directions. Very odd ...

Arfa

Reply to
Arfa Daily

Hi Meat. See reply to Adrian above. Here's a little aside you'll no doubt find amusing ... Got in this afternoon, and number 2 daughter was doing some door painting for us in the house, and had MTV on. At pretty near full volume, shaking the house ...

Tonight, I'm watching some TV, and the sound is 'wrong'. A bit quiet, and slightly 'thin' sounding. Then some incidental music came on the programme, and it had a very odd 'raspy' sort of a sound to the bass beat. Then I realised what is wrong. She's only gone and buggered the TV set's built in sub. Bloody kids. Who needs 'em ?

Arfa

Reply to
Arfa Daily

Yeh didn't read it well enough the first time.

Mine has his own gear but I did once come home to a house with rattling windows from the 5.1 system in the tv room. Luckily I like it loud myself and have 4 Infinity towers, a dual 5.25 center and floor firing 150 WRMS Kenwood 12" sub thats virtually indestructable after replacing the stock 12 with a Cerwin Vega 12 sporting a 3" voice coil :)

Hopefully they were at least fun to make.

Reply to
Meat Plow

I guess they probably were ... :-)

The sub in the TV is built into the stand. This is a hulking great Tosh CRT set, remember. I seem to recall that it is a separate box, before it gets screwed into the stand, but I can't remember whether it's screwed from the top, under the TV, or from the sides. I seem to think that it has its own set of wires going to output sockets on the the back of the TV though, so maybe I will finish up just disconnecting it, and shoving another sub on there, hidden behind the TV. I've currently got it shut off in software. Leaves me with bloody awful sound, but at least no rattly rasp ...

Arfa

Reply to
Arfa Daily

I can't recall ever using the int speakers on my Pana 51". The speakers on my bedroom set a now defunct Olevia are piss poor and that's a good review. I hooked a Logitech 5.1 set of pc speakers to it to cure that problem. One problem I have from the tv audio is when the display is set to dark or medium room I get a 400hz tone from the sets audio. It's barely there but annoying. Must be from the circuit that cuts the voltage down on the CFLs somehow getting into the audio. Fuck it I'm not going to worry about it because I watch it at full power, just have to turn a light on in the room.

Reply to
Meat Plow

">>>>Here's a little aside you'll no doubt

The sound is actually quite good on the Tosh. I don't watch a lot of films or 'big sound' drama, so I've never really bothered with 5.1 amps and the like. The set has built in Pro Logic surround, with external rear surround speakers. Good enough for what I want it for.

Anyways, bit of a result today, with any luck. I was on the phone to a mate at a shop that I do work for, and happened to mention it to him. Apparently, the sub is located inside the TV's back cover, and the box facing forward in the stand, is in fact the 'centre' speaker for the surround. Obvious now I think about it ... So, seems that he has a scrapper at the shop, and he says that I am welcome to the sub out of it, so I'll pick it up when I'm in there on Friday :-)

Arfa

Reply to
Arfa Daily

Arfa Daily wrote: I can't for the life of me think what that problem could

Perhaps it's a "flywheel" PLL sync issue around the part of the circuit that de-interlaces and reads lines of video into the digital frame buffer.

However it has got problems with recognising the pixel timing of new lines in the first field, comes in sync after a few lines, successfully uses the now found timing to digitise the secong field, then, er, forgets?

--
Adrian C
Reply to
Adrian C

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.