Electronics > Repair
Transflective LCD polarizer orientation
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CharlieD:
This topic is very interesting. I change the polarizer film of a Tek TDS2002B scope with bad polarizer fml (a typical fault) and although it improved compared to how it was, it was left with a purple hue where it should have been black, see pics below for comparison.


--- Quote from: Lomax on January 21, 2020, 07:04:57 pm ---Confirmed: FSTN LCD displays need a retardation film on the front and on the back. 

(Attachment Link)

What chance do I have of finding these films?

--- End quote ---
Any suggestions to improve this and what could be the causes?

How looks like


How should look like
pete1zed:
Hi,

It is possible that the direction of polarization is not correct.  You could check this roughly by rotating the film until you see the correct display colours.

It is possible that there a retardation layer missing in the replacement film, or present but not wanted.  See
https://tinyurl.com/retardation-layer-1

Let me know if I can send you a free sample with the retardation layer.

One issue is that you may have inadvertently peeled off the old film, but left the original retardation layer in place, which is almost impossible to detect.
I had a case where I spent a lot time trying to find the correct polarizer, and then discovered I'd not removed the old clear plastic retardation layer. 
Therefore I had two retardations layers by accident.
After I removed the original retardation layer, the regular LCD polarizer worked fine.  Just check that you removed all the film by checking the exposed layer is glass and not plastic....

.... except, if you can't get replacement film with the polarizer, you'd want to ensure the old retardation layer is in place so it can be re-used.

Of course, there may be no retardation layer at all.

This is  a confusing answer I know, so if you do find the solution, please reply here so we can all benefit.

Also,
(1) Can you just buy a whole replacement display from Aliexpress etc? 
(2) Have you tried to contact Tektronix for the information?
(3) Good luck...


When running into a similar problem, I got the following answer from www.mecanusa.com
I think it is also possible to send them a small sample of the original and they will try and figure it out. 


-Pete


----------------
Thank you for contacting Mecan.

Here below link is for our lineups of retarder film.
https://www.mecanusa.com/polarizer/phasedifferencefilm.htm

Unfortunately, we have no knowledge of the type of polarizer used in calculator
and we don't know which kind is appropriate for you.

If you would like a sample, we can provide small pieces for free.
Size is about 8 x 8 cm, and we will send you with regular air mail from our US office.

You may also want to try a circular polarizer.
A circular polarizer is made by laminating a linear polarizer and a quarter waveplate together,
so it might be that the original polarizer may have been a circular polarizer.

Here below link is for our lineups of circular polarizer film.
https://www.mecanusa.com/polarizer/circularpolarizer.htm

Unfortunately, there is no self-adhesive layer in either product

Click here for our adhesive sheets for optical films
https://www.mecanusa.com/polarizer/adhesivefilm_MPD62.htm

If there is any other request or inquiry, please contact us anytime.
We look forward to your reply.

Best Regards
Ryo
CharlieD:
Hello Pete1zed:

First of all, thanks for your answer.


--- Quote ---It is possible that the direction of polarization is not correct.  You could check this roughly by rotating the film until you see the correct display colours.

--- End quote ---

I did, it was either this colour, or a kind of white colour in the other extreme case of polarization direction, unfortunately I don't have any pictures of that. I decided this was the best direction of polarization in terms of contrast/colour.



--- Quote ---One issue is that you may have inadvertently peeled off the old film, but left the original retardation layer in place, which is almost impossible to detect.
I had a case where I spent a lot time trying to find the correct polarizer, and then discovered I'd not removed the old clear plastic retardation layer.
Therefore I had two retardations layers by accident.
After I removed the original retardation layer, the regular LCD polarizer worked fine.  Just check that you removed all the film by checking the exposed layer is glass and not plastic....
--- End quote ---
I'm not really sure, I'm gonna open the scope and check this, and I will reply.


--- Quote ---(1) Can you just buy a whole replacement display from Aliexpress etc? 
--- End quote ---
Too expensive for me  unfortunatelly, It would be more expensive than the scope itself (cost around 50 bucks with a bad channel, already repaired). Also, I'm from Cuba, get spares and buy online is almost imposible here.


--- Quote ---I think it is also possible to send them a small sample of the original and they will try and figure it out.
--- End quote ---
Same problem, I'm from Cuba, send something to another country is difficult.

I asked here hoping that someone had a similar issue, but I'll find out everything I can, I really wish that the scope can get the original display colour. I'll be posting updates in the future.

BTW, the polarizer filter I'm using is this:
https://3dlens.com/linear-polarizer-film-200x250mm-with-adhesive.php

A friend send it to me from USA.

Many Thanks.
Lomax:
Nice scope! And an absolute bargain at $50  :-+

I'm afraid what @pete1zed is saying WRT the missing retardation layer is most likely correct. I'm sorry to hear it's so difficult to place international orders from Cuba - maybe your friend in the US can help get you at least a sample piece of film with a colour correction (retardation) layer? Should be possible to send as a letter... Please let us know how you get on!
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