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Thomson 'scenium' 28" lcd has greenish tint.

 
Alastair
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I know this is mainly a Vintage Forum, but I know a lot of you guys also do modern stuff too...... :qq1

Came across this set today in work. It was dead--usual thing, dried out caps in PSU.--Nice easy start to the day!

As the set is pretty well made in comparison to a lot of others, and is still quite stylish, I rather fancied it myself.
--Problem is, the picture is either lacking blue or is excessive green. Its the same and more obvious with the colour turned right down.
Could this be the aging of the LCD panel itself--Ive heard that the UV the backlight tubes develop, destroys the dyes in the panel over the years....

Are there options to adjust such effects out for a while....?

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Topic starter Posted : 23/08/2013 7:16 pm
Refugee
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Don't you have to do a firmware upgrade after the caps have been changed on those flat sets?

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Posted : 23/08/2013 10:23 pm
Doz
 Doz
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Not just a grotty scart plug when feeding in RGB?

I'll go and see if my B&K has an adaptor for this model :aaj :aaj

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Posted : 23/08/2013 11:48 pm
Alastair
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Not just a grotty scart plug when feeding in RGB?

I'll go and see if my B&K has an adaptor for this model :aaj :aaj

Ah--Now you may have something there....

I had tested a Philips 32" LCD earlier and played a film that I'm not familiar with. I thought the colour was 'Orrible. The guy (Brother-in-law) who now has that Philips is pretty happy with it--so doubt that the colour is 'Orrible now
Same film, same DVD player, same scart, so its possible.

If not--I'll get the old bulb-bopper to it! :aaj

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Topic starter Posted : 24/08/2013 1:14 am
Refugee
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Bat capacitors do give out a pretty harsh factory reset and a service code will often need to be entered via the remote. It varies from one model to another.

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Posted : 24/08/2013 11:46 am
Haerial
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A friend of mine who does repair lcd & plasma sets has found that some back lights to go 'off white' as they age. Also many modern sets have a hidden service menus for adjusting the grey scale amongst other settings.
Be careful though. It is easy to destroy the set when in these service modes.

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Posted : 27/08/2013 11:27 pm
Red_to_Black
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Don't you have to do a firmware upgrade after the caps have been changed on those flat sets?

Bat capacitors do give out a pretty harsh factory reset and a service code will often need to be entered via the remote. It varies from one model to another.

Sometimes the eeprom gets corrupted due to the amount of ripple and hash on the supply lines (Samsung and a few other makes) and if the eeprom gets replaced it will probably need to be either a blank one (some older Samsungs) and may need slight re-programming/setting up, or sometimes the manufacturers 'default' eeprom may need to be obtained and again some setting up may be required (JVC, Vestal, Panasonic, Sony, LG to name a few).
Some Philips need the specialist COMPAIR tool, and some makes/models may need special jigs.

if a FW update is available and it cures other specific problems then often it is prudent to do this at the same time during the repair.

The operative word here is 'may', a lot of the time just replacing the caps effects a complete cure, with no setting up required at all, just the luck of the draw really, and not a hard and fast rule.

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 27/08/2013 11:52 pm
Refugee
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That is absolutely spot on.
With a bit of fiddling about it may also be possible to extract a copy of the firmware from a working set with the risk of writing off both sets.

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Posted : 28/08/2013 9:42 am
Alastair
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Eee Gads--

What happened to the days that we just needed to tweak a few pots and all was well!

F/W updates, hidden service-menus--where will it all end! :ccb

Ive since got the set home--Ive yet to fire it up with my sources here, so we'll see how it looks when I do....
--If there's going to be much hassle with it--I'll take it back and sell it on in the shop --As it is! :aad

--Probably a 28" set like that we would sell on for only a tenner anyway! :aaj

Ive since done a number of similar sized --all be it not as well-made or nice-- and they are pretty good with regards the picture quality..... ttt:

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Topic starter Posted : 28/08/2013 7:35 pm
Alastair
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Reason for the fault discovered.....

As I have scrapped a few LCD sets over the last week, I stripped down the screen ass. of them--just to see how they are made.

The LCD panel is Very Thin--so no surprise we see lots of cracked ones! Its only about 1.5mm thick--and thats on a 42" set!
--At least this set has a proper thick glass panel 'implosion' shield in front of the panel! :aad

The layout goes like this--

Plastic polariser film, LCD glass panel--These two parts comprise the LCD panel and are made as one piece.

Then we have the light deffuser, and finally the backlight light-box, containing around 10-15 thin CCFL lamp bulbs running across the back of the light-box, held in small plastic clips--They can be removed fairly easily without damage .

The deffuser comprises two thin flexible frosted type plastic sheets and one hard white plastic plate about 2.5mm thick.
These are held in the frame of the light-box and the LCD panel rests directly on them. There are a couple of small support posts stretching from the back of the light-box to hold the centre of the diffuser firmly.

I plucked up the courage to remove the chassis and the LCD module from the set to take a look how long the CCFL tubes were--That was the original plan anyway.
After much careful fiddling round, I released the LCD panel from the LCD module/light-box frame, to see a rather yellow coloured deffuser!

The thin sheet deffuser sheets were the first under the LCD and were still reasonably white/clean in appearance.
The thick sheet deffuser nearest the CCFL tubes had a distinctly yellow appearance, but was white at its covered edges where it was sandwiched between the frame.
--The white surface of the light-box also is a little discoloured too. I cleaned this as best I could, but it isnt perfect. A respray in brilliant white matte paint I think is needed, but to do that, I'll need to remove the 10 CCFL tubes, --and when I do, I might as well replace them.

It Looks like the sheet has been affected by nicotine, although the rest of the set doesnt really look to be from a smokers house--Maybe the UV has affected the plastic of this first rigid panel--like it does with uPVC windows--maybe thats where the 'myth' came from!....

Much cleaning with alcohol, Brasso, and a few other things has removed around 90% of the yellow, but its still just very slightly there.
Reassembly has shown a much better grey-scale, and quite watchable although isnt spot on.

Next large screen set I scrap--I'll save the diffuser sheets, cut them down to size and replace them all in this set....

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Topic starter Posted : 31/08/2013 12:47 pm
Anonymous
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Very interesting. The fact the discolouration can be removed suggests airborne contamination (open fire or smoking) rather than UV as that releases compounds deep into the surface (google yellowed Lego bricks).

The LCD is of course two glass panels with a very very small exact spacing containing the magic synthetic organic liquid The thin film transistors are on an inside layer as are electrodes. Between the front plastic and LCD glass is a stripe dye filter. It can fade both from sunlight and bright static pattern (Large 42" call centre LCD HDTV screens prove this, can't remember if I photographed them) The polariser layer is very thin and on rear and front sides so that the panel is only fed polarised light and the second top one ensures that as the LCD rotates polarisation the pixel goes from clear to opaque. Usually the top has also a thicker plastic protective layer just to hold all the glass fragments. Then you have the outer protective glass for mechanical stability and scratch resistance.

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Posted : 31/08/2013 2:21 pm
Alastair
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An update on this set--for future reference....

Two days ago in work--I scrapped two 27" LCD sets that had the same panel/backlight as this one. The panels were cracked so all the usable parts were kept, but one of the sets--a Sharp was particularly clean and dust-free inside.

I stripped out the light-box complete with its driver-board.

Long story short--I replaced the light-box complete in the Thomson, and the set is transformed.--Even though I had cleaned all the diffuser so that there was no apparent staining and even painted the backplane of the box, the greyscale was still poor.

Low-lights were sorta reddish/brown, mid-lights greenish, and highlights yellowish. very apparent on a greyscale step-pattern.

I can only assume the actual back-light tubes had de-generated and had gone yellow in their light spectrum.

I now have a near perfect greyscale, and haven't altered any of the service-menu settings--Still waiting for the remote I ordered.....

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Topic starter Posted : 04/09/2013 10:08 pm
neil1974
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Nice one Alastair :aad .

Cheers,Neil.

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Posted : 04/09/2013 10:13 pm
Red_to_Black
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When the tubes are worn, they are a sort of yellowish/pinkish colour, if you have a read of Sidebands thread here: viewtopic.php?f=17&t=5371

This explains some of it.

Usually either the hardware sensing circuit shuts down the inverter, and sometimes the soft/firmware shuts the inverters down too. Some like SB's Sharp have both soft and hardware trips, and in this case an error counter which puts the set in standby permanently until the error buffer is cleared, even if the lamps are changed the error buffer still needed to be cleared first.

As to this particular set without a model number we don't know which chassis is fitted, some cheaper models will show an awful picture, but Vestal sets don't, it really all depends on the set, again there are no hard and fast rules but in general premium branded sets usually won't allow an inferior picture to be shown.

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 04/09/2013 10:28 pm
Alastair
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Ah--Now That is interesting!, It helps me out with a Toshiba 32" set actually on the bench right now--No Backlights, and obviously a very well used set by its internal appearance!...

Anyway--the Thomson is a 27 LCDB 03BU and is a pretty old set, so maybe that particular (irritating from a service point of view) feature doesn't apply.... :aad

One thing I noticed, is the Thomson as a set got extremely hot during normal use. It has two fans fitted so as to draw air through the space between the backlight-box and the main chassis....

I have arranged a 47 ohm resistor from the 12V rail to make them run (reasonably quietly) at all times the set is showing a picture.
--Makes a huge difference to the temperature..... :)

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Topic starter Posted : 04/09/2013 10:41 pm
Red_to_Black
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The Toshiba is more than likely a Vestal set too Alistair, it (probably) has a chassis type on the back something like 17MB XX if it is Vestal, where the XX is two numbers eg. 17MB61 etc. etc., I have quite a bit of generic Vestal service info. but I no longer have access to Toshiba Technical, which obviously rules out getting specific firmware etc. for the Tosh.

Edit:
I have a circuit diagram for the Thomson set, but it is not much use, it has no inverter diagram (virtually none of the LCD TV manuals do!), mainly because it is considered non serviceable, and a replacement being the service solution. :bbd

The Chassis type is LCD03, and the 1st issue diagrams are dated 2003-2004 (which partially explains the chassis type designation), I don't think it was made by the Thomson (we all know and love :qq1 ) as the component reference numbers don't match Thomsons usual scheme, it was likely either badged up or made after Thomson (the consumer electronics part) was sold off to the Chinese.

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 04/09/2013 10:48 pm
Alastair
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I'm having difficulty in accessing the service-menus of the set. Either the remote I now have isnt right--some functions are incorrect, although the 'Exit' button needed for the access is correct--Or I haven't the right access procedure....

I was curious as to what the 'age/time of use' counters read, be interesting to see just how much use this old duffer has had!
Picture is very presentable now, so realistically I don't actually need to enter the service-mode at all--Just curious.....

As to those Tosh sets--I now have two, one that has no 12 and 24V from the PSU, but has the 'PSU On' signal, and the other with no backlight, and a third of the same type I haven't looked at yet--I feel some panel swapping coming on!
Both appear not to be the usual 'Vestel' types.....

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Topic starter Posted : 06/09/2013 8:12 pm
Mkstevo
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One thing I noticed, is the Thomson as a set got extremely hot during normal use. It has two fans fitted so as to draw air through the space between the backlight-box and the main chassis....

I have arranged a 47 ohm resistor from the 12V rail to make them run (reasonably quietly) at all times the set is showing a picture.
--Makes a huge difference to the temperature..... :)

The shop I worked for ended up with a Thomson set that was written off (by Thomson) as uneconomic to repair with an intermittent failure to come out of standby when warm. Well, I say written off. It was awaiting Thomson collecting the set for repair for months and months, then they went 'bust' and pulled out of the UK market. Eventually CI(H) [Euronics] from whom we'd bought the set refunded us for it. As LCD sets were still rather expensive, in a slack period I decided to have a look. I spent ages looking at the power supply, which from memory spread across a number of boards, each with their own chopper circuits and transformers to generate the various supplies required. Much time later an invisible dry joint was resoldered in the standby PSU, and the set put on long term test. It worked well and in two or more months of testing never gave any problems again. But boy did the power supplies run hot! In the customer's house it had been sited in the glare of a west facing window which combined with the extreme heat generated by the PSU had probably caused the problem in the first place. I had to wrap it in a duvet to get it hot enough to 'fail' in order to test it.

To come (finally!) to my point, I fitted a computer fan in it. This was powered by the 12V supply when 'on' and the always 5V supply in standby, with a simple diode pair in the supply feeds. This kept it reasonably quiet in standby, and with the set on, the volume was normally enough to drown out the fan even if you pressed your ear up to the case. It certainly stirred the air enough even when in standby to reduce the heat of the PSU to a much more comfortable level.

We sold it at a low price and never saw it again.

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Posted : 11/09/2013 7:37 pm