Hi, please make sure that you have removed any additional protective layers from the film. Have you tried 45degree rotation ?

Aui wrote on 2023-03-12, 12:16:

Hi, please make sure that you have removed any additional protective layers from the film. Have you tried 45degree rotation ?

Yes I did remove them, also tried 45 and reversing the film. The best quality for brightness and white blalance is at 90 but the colors are reverted.

I've been doing some experiments with this myself - I decided to buy a Toshiba T1910CS with a bad front polariser thinking it would be simple to fix. Polarisation is unfortunately a rather complex topic - linear polarisation is all that's required with a TFT, but with passive matrix DSTN panels it seems to me that there's more to it. I haven't been able to find good discussions on english language forums for computer type polarisers and mostly when I see polariser discussions it usually just ends with 'replace the screen' - sadly that's not possible with many of these laptops, your Toshiba 2140CDS uses an HPA DSTN panel that is probably the only panel that can work with the signals being sent to it.
On mine it's a Toshiba TLX-8101S-C3X that is essentially unobtainable and DSTN panels this size generally aren't available, so I've put the time into cleaning off the polariser from mine. It did some interesting damage - the polariser breaks down into acetic acid / vinegar type stuff hence the name 'vinegar syndrome' and on mine, the vinegar caused surface rust all around the front edges of the panel.

I have a similar problem to you in that a regular polariser doesn't give a clear or colourful picture (except inverted which is useless), at any angle I've tried either front-ways or back-ways. The ones I've tried so far are linear polarisers and I can compare them with the remaining segments of a damaged original DSTN polariser - which looks great with nice black levels and bright colours.

I recommend trying out some reald-3d glasses to test polarisation:

They have circular polarisers on each lens, one is clockwise and the other is counter-clockwise. A circular polariser is an additional 'quarter wave plate' layer that as far as I can tell makes the light polarisation effect into one-way, beyond just linear polarisation. If light goes through a circular polariser (circular + linear polariser) then to work with it, the polariser on the other side needs to have a matching circular polarisation. I do not know the proper terminology for this yet.
These reald-3d glasses have different direction circular polarisers and I found that the left eye lens gives a good picture. According to here that's a counterclockwise circular polariser: https://www.diyaudioandvideo.com/TV/3D/Theater/

Here are some examples of the different types of polariser, some re-used offcuts of linear polarisers from broken TFT screens, the two lenses of some reald-3d glasses and the original polariser remains:

I haven't yet found a good replacement, I tried cold-light OLED polarisers for an iPad but the circular polarisation seems to be the wrong way or on the wrong side from the glue. Consider trying this place but they don't say which direction the circular polarisation goes: https://3dlens.com/lcd-polarizer-film.php
Beyond that, I think trying out different types of oled polarisers might work if it's possible to get one that goes the other way, mine were meant for replacing the front polariser of an ipad pro screen, perhaps there are ones for the other side. It seems that beyond clockwise and counterclockwise, for purchasing they can be referred to as left-handed or right-handed. No idea which is which yet.

Right now - those glasses with lenses from 2x reald-3d glasses are required to use the laptop 😁

Thermalwrong wrote on 2023-03-13, 00:35:

I recommend trying out some reald-3d glasses to test polarisation:

They have circular polarisers on each lens, one is clockwise and the other is counter-clockwise. A circular polariser is an additional 'quarter wave plate' layer that as far as I can tell makes the light polarisation effect into one-way, beyond just linear polarisation. If light goes through a circular polariser (circular + linear polariser) then to work with it, the polariser on the other side needs to have a matching circular polarisation. I do not know the proper terminology for this yet.
These reald-3d glasses have different direction circular polarisers and I found that the left eye lens gives a good picture. According to here that's a counterclockwise circular polariser: https://www.diyaudioandvideo.com/TV/3D/Theater/

Thanks for your answer.
Yes, I've tried some Real-3d glasses and looking trough one of the lenses the image is much better in terms of colors and brightness than the Aliexpress film (and no inverted colors). Still not as good as the original film but If I could find a big sheet of film like that I would use it.
The Aliexpress film is so bad that I don't even want to stick it to the LCD.

It's not that the polariser you've got from Aliexpress is of poor quality, with a TFT / active matrix it should be fine. But because the circular polarisation doesn't match it'll always be ineffective at matching the polarisation of the polariser on the internal side of the DSTN LCD panel, unless the internal polariser is also replaced.
Notice that where I've got the other reald-3d lens up against the screen it matches the polariser offcuts from TFTs, so only works as a linear polariser.

Also for the reald-3d glasses, the left side's lens does have to be rotated quite a bit to get the colours right - like you say not 100% but it's good. Black becomes kinda purple but it's the closest I've yet seen.

Thermalwrong wrote on 2023-03-13, 14:58:

It's not that the polariser you've got from Aliexpress is of poor quality, with a TFT / active matrix it should be fine. But because the circular polarisation doesn't match it'll always be ineffective at matching the polarisation of the polariser on the internal side of the DSTN LCD panel, unless the internal polariser is also replaced.
Notice that where I've got the other reald-3d lens up against the screen it matches the polariser offcuts from TFTs, so only works as a linear polariser.

Also for the reald-3d glasses, the left side's lens does have to be rotated quite a bit to get the colours right - like you say not 100% but it's good. Black becomes kinda purple but it's the closest I've yet seen.

Okay, it's been a while but I've made some major progress on this. Looking up Gameboy Pocket polariser repairs, on reddit and facebook they've found that regular linear polarisers that are great for the original gameboy give a different colour tone to the original Gameboy Pocket polariser: https://www.reddit.com/r/Gameboy/comments/nr6 … group_recently/

I found another video where they swapped the polariser and had the same low contrast image: https://www.youtube.com/watch?v=gRmgfX_tFto - with what I've seen now I think they had the polariser angle correct at 45 degrees but the compensation film magically brings in the colour.

Eevblog has a good technical discussion on the topic: https://www.eevblog.com/forum/repair/transfle … zer-orientation
I found through those links that there's an optoelectronics seller on Aliexpress selling "FSTN front polariser film" which gives more information: "Polarizer film for FSTN LCD.
Front polarizer film for dashboard, gameboy calculator and so on. 570nm 45°"
What does that mean? The 45° means that the linear polariser is at a 45 degree angle to the square shape of the polarising film. The 570nm is telling, that fits in the range of a "full wave plate" according to this site:
https://www.apioptics.com/product-category/pr … retarder-films/

This site's got some good visuals of how the front polariser stack is put together, with a 'retarder film' or compensation layer between the glass and the front-most polariser:
http://www.sunnypol.com/EN/product.aspx?BaseI … =111&CateId=111

That's why a lens from passive 3d glasses works part-way, because it's got a compensation layer as well, but that's only a quarter-wave waveplate/phase retarder.
I thought that OLED polarisers might work since they've got the same compensation layer but reading into it, those don't work at all because the setup is specific to OLEDs. I tried buying an ipad pro polariser (or 5) and they don't work for anything, not TFT or these STN screens.

I wanted to try out this 'tape method' that reddit talked about and a few other materials. I tried some real cellophane from a roll and that didn't do anything useful. However some random cheap clear 2" wide packing tape did something impressive:

That looks pretty good! Interesting how the polarisation is lined up correctly and shows this sepia tone display, but putting some tape in between the glass and the polariser makes that much difference.
The screen itself has no polariser on it in this pic, I used a polarizing filter attached to my camera lens set to the correct polarisation angle of 45 degrees.
The tape isn't stuck to the screen yet, I folded over the ends so I can handle it and it's holding to the glass with static, very handy for experimenting 😀 The tape behaves the same facing either way, just the angle has an effect.

And a similarly good result with a monochrome LCD, eventually I found that somewhere around 20 degrees downwards from the upper line of the screen gives a great result:

Proper greyscale again!! The film compensation is the same for these 'paperwhite' greyscale LCDs as it is for colour passive matrix LCDs, because it lets them do proper black and white on the LCD, which enables the use of colour filters to make colour.
Notice as well that the proper polarisation lineup in the areas where there's no compensation film results in the sepia tone image as the colour one does. Something to watch out for if you're doing this 😀

From there I did some tests with different tapes, different angles and found that overall 20 degrees works best. I had some little snippets of the original polariser to compare the colours, contrast and black level with:

Once that was all decided, I laid strips of tape onto the glass of the LCD and getting them aligned was difficult, there are air bubbles in there too. The only polariser I have didn't fit at 45 degrees so it got up into parts too and it's got double sided tape at the edges holding it all in place:

This is a Toshiba TLX-8101S-C3X LCD from a T1910CS but it's running in my Toshiba T2400CS for reasons. This is equivalent to the Sharp LM64C089 / LM64C149 but what I've found here should be applicable to most DSTN LCD panels.

And the end result from a better angle showing some colours. It's not perfect and it probably won't stay like this since I might try the FSTN front polariser from aliexpress to see how it is. It's much more usable now:

Great Job, Looks good and respect for the persistance....

Aui wrote on 2024-10-05, 12:35:

Great Job, Looks good and respect for the persistance....

Thanks 😀 The project is still ongoing until I can find something that gives an even look without gaps and determine the important elements of this film so that other people can source it more easily. I've got closer and have determined one material works at a very specific thickness.
BTW my previous post might be wrong, 570nm doesn't indicate the type of waveplate it is, just the frequency it operates on? It could still be a quarter or half wave plate and I can't find any information to confirm what FSTN LCD panels use. So I shall stumble in the dark until I find what works best. My results are pretty good so far, now I can use some cheap cellophane in combination with a cheap linear polarizer to fix a DSTN panel where the original polariser went bad.

First of all for reference here's a picture of my Compaq Contura Aero 4/33C - which is a similar 640x480 DSTN LCD panel. It's definitely not the best but the polariser isn't failing on it yet:

The picture looks 'good' but it always feels like the contrast is not in quite the right spot, it's either too dark or too light and that's how DSTN is.

The other day I got some 20 micron polypropylene / cellophane, a huge roll of it and I was rather disappointed to find it looked like this:

It just couldn't get the colours right and was always washed out with either a red or sepia tone. Seems like 20 microns is too thin for the birefringence / phase-retardation to match the LCD panel. Now what do I do with this huge roll of useless film.

Then I got some "Archive Standard 12" VINYL LP Record ALBUM Protection Sleeves" vinyl covers because they use biaxially oriented polypropylene film (BOPP) which is supposed to 'retard ultra voilet light' so I thought maybe it would work as a phase retarder, but no it did nothing at all. So I don't recommend buying random films, this is rather specific stuff.

Now here's a test with 30 micron polypropylene and I was very disappointed to discover that it didn't do anything useful, giving a poor contrast picture even with two layers, one layer was worse.
Check out todays tests, thankfully the 25 micron stuff came in and the results are 'pretty good'!

I'm happy with that although it's uneven, because it's far easier to install. You get the front polariser at the correct angle which is usually 45 degrees, then get a sheet of the polypropylene and put it between the glass and the polarizer sheet, rotate it around til the colours look correct then use a marker to mark the edge points on the film when it's at a good angle. Cut that down and voila. Now neither the polariser or 'fstn compensation film' are glued to the LCD and that's the tricky next step - they are instead held on at the corners with double sided tape but I'm happy with the result for now, til I find some better graded polypropylene film or another material that works better:

Still waiting on the proper polariser sheets to arrive - the ones I'm getting are regular linear polariser sheets without adhesive which I think will work fine once the laptop's LCD bezel is back in place. That's one of the reasons I'm doing this btw, I want to be able to find the right angles / install a polariser without glueing it down just yet. But that FSTN polarizer on aliexpress while obviously the best option, requires attaching to the LCD with its glue to work right and I'm not confident in installing an LCD polarizing film without getting bubbles / dust in there.
Going with this method means I can just leave the polariser / compensation film in front of the LCD and use it as is for a while.

edit: though I have no access to the full articles, it seems that Keigo Iizuka made some interesting findings back in 2003 in making a regular LCD into a 3d display. He stated that 25um cellophane works well as a half-wave plate: http://individual.utoronto.ca/iizuka/research/cellophane.htm

Came here looking for repair options of Highscreen Handy Organizer (a DOS palmtop with b&w CGA). I suppose, that compared to thread above, in my case it should be pretty straightforward? 😁 Anyway, I am looking at aliexpress, there are many offers with "LCD repair film", "polarizing film" etc. But as far as I see, they do not mention if it has some sort of adhesive. And I think I need one with adhesive. So - any recommendation, where to get such polarizing foil?

rasva wrote on 2024-11-16, 10:44:

Came here looking for repair options of Highscreen Handy Organizer (a DOS palmtop with b&w CGA). I suppose, that compared to thr […]
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Came here looking for repair options of Highscreen Handy Organizer (a DOS palmtop with b&w CGA). I suppose, that compared to thread above, in my case it should be pretty straightforward? 😁 Anyway, I am looking at aliexpress, there are many offers with "LCD repair film", "polarizing film" etc. But as far as I see, they do not mention if it has some sort of adhesive. And I think I need one with adhesive. So - any recommendation, where to get such polarizing foil?

Since that looks like a gameboy with the rather green screen, you should be fine with any polarising film. If it was more black & white/grey looking then you'd need FSTN polariser which has the extra retarder layer to alter the colour profile.
You should try to find matte / non-glossy polariser that's adhesive to match the original polariser. The polarisation angle (0 deg, 45 deg, 135 deg etc) you might be able to determine from that line forming on the screen, looks like it's probably a weird angle so you can go with a 0deg or 45deg and move it around from there. Hopefully it's just the front polariser that's gone bad, since you'll need to test the screen with the front polariser removed to check the polarisation angle.

I did replace a polariser on a similar size screen the other day, on a Sony Vaio Picturebook PCG-C1 with a glossy non-adhesive polariser and the screen looks good but because it's non-adhesive I can clean out dust and not worry about bubbles when gluing down the polariser. Using a non-adhesive polariser has a serious catch though, in that if it can touch the clean glass of the LCD it'll start to stick together and end up looking weird. To resolve that I used 1mm thick double sided tape to adhere the new polariser in place and separate it from the LCD (unless it's pressed on of course).

@Thermalwrong, any chance you can point me to the latest polarizer you found the best for DSTN displays?
I experimented with multiple types of polarizers in the market and did not get great results. I even tried to recover original polarizers that were on the DSTN display and I noticed that something special is going with them, especially for the two layers (one in front of the backlight and the second one in front of the LCD).
Any clue is really appreciated.

Also, something interesting I observed is that, when I cleaned the adhesive on the LCD and the polarizing sheets and put them back together, I started to get a negative image. This is telling me that perhaps the adhesive has also a contribution in the formation of the image. Any thoughts on that?

ahmadexp wrote on 2024-12-27, 16:41:

@Thermalwrong, any chance you can point me to the latest polarizer you found the best for DSTN displays?
I experimented with multiple types of polarizers in the market and did not get great results. I even tried to recover original polarizers that were on the DSTN display and I noticed that something special is going with them, especially for the two layers (one in front of the backlight and the second one in front of the LCD).
Any clue is really appreciated.

Okay so, my recommendation for the front polariser is still this one: https://vi.aliexpress.com/item/1005006357535916.html
If you're taking off both the outer (front) and inner (rear) polariser films to replace them, with DSTN it turns out that the rear polariser has its own slightly different retardation film.

Regarding the adhesive, the adhesive is optically clear and has no other optical properties, it doesn't do the phase retardation. However the retardation layer is a separate film from the polariser and can come off separately from the polarisation layer so when cleaned off it might get removed with the glue. Oddly I was able to recover the inner polarisation layer with its retardation film from a much later DSTN LCD panel (from a Satellite 2140CDS I think), but otherwise I've never recovered a polariser from a DSTN with the retardation layer intact, it tears very easily especially where the glue has gone bad.

I did some experiements a couple of months ago but don't remember exactly what With my truly busted LM64P83 LCD with the front & rear polariser that had broken down, I found that unlike the front polariser, the rear / inner polariser needed a thicker or possibly different level of retardation film. Specifically I found that some vinyl record sleeves "storage.boutique 12" Vinyl Album ARCHIVE STANDARD Protection Sleeves" worked for that while they didn't work for the front DSTN polariser.