Author Topic: Small LCD module polariser repair  (Read 1647 times)

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Offline gnif

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Small LCD module polariser repair
« on: August 09, 2016, 08:31:37 am »
Hi All,

I have been asked by a friend to repair a Yamaha amplifier from '93 which has a LCD backlight by a 12V globe. The rubber grommet that held the globe in place has failed and the globe was resting on the back of the LCD, which has overheated and destroyed the polarising film. The LCD is configured to be a negative display allowing light through the active segments, so the new polariser needs to be as opaque as possible on unlit segments.

I tried to use a polariser from eBay for an iPhone, but the results were terrible. I am guessing these early LCD modules used some other kind of polariser.

Does anyone has any suggestions of a suitable replacement filter?
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Offline NottheDan

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Re: Small LCD module polariser repair
« Reply #1 on: August 09, 2016, 10:02:27 am »
Huh? Don't you usually just turn the polariser around and put it on backwards to get that? Certainly always worked with watches.
 

Offline amyk

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Re: Small LCD module polariser repair
« Reply #2 on: August 09, 2016, 10:39:21 am »
If the module got hot enough to damage the polariser, I think the liquid crystal would've also suffered.
 

Offline gnif

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Re: Small LCD module polariser repair
« Reply #3 on: August 09, 2016, 12:02:36 pm »
Huh? Don't you usually just turn the polariser around and put it on backwards to get that? Certainly always worked with watches.

I have done some further research and it turns out I used the wrong polarizer, modern phones use a circular polarization where these displays used a linear polarizer.

If the module got hot enough to damage the polariser, I think the liquid crystal would've also suffered.

It was only warm enough to heat the film which causes it to lose its properties over time. Polarized film is created by carefully stretching plastic, heating it allows it to return to its prior state. The display works fine, but has a spot where it was warm/hot which is not contrasting enough and hard to read. I have confirmed the display is fine by moving the old polarizer across to an undamaged edge to test.
« Last Edit: August 09, 2016, 01:19:10 pm by gnif »
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Offline Kilrah

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Re: Small LCD module polariser repair
« Reply #4 on: August 09, 2016, 02:19:35 pm »
Yup, linear polarizer and changing between "white on black" and "black on white" is done by simply rotating one of the polarizers by 90°.
 

Offline SeanB

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Re: Small LCD module polariser repair
« Reply #5 on: August 09, 2016, 02:31:35 pm »
Have you tried using the polariser out of an old LCD monitor? One side has the colour filter as well, but the other side will not. You just need to split the 2 thin glass plates apart and clean off the cholesterol from the surface, then see which side works best on the front, and then mark the correct darkest polarisation angle to cut along that to get a smaller glass and film to place there.
 

Offline SeanB

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Re: Small LCD module polariser repair
« Reply #6 on: August 14, 2016, 12:37:16 pm »
Did a quick test on Friday....



Seems to work using an old scrap small LCD display as the donor for the glass and film.
 


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