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Lcd cold effect?

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767Geoff

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Lcd cold effect?

Post02 May 2017, 20:22

Hello,

I have a beautiful 0614/06lc NOS condition with original labels on both case and crystal intact. The module looks perfect, no corrosion and is functioning.

The LCD panel is faded when viewed at 90' to the plane of the panel. This improves as one moves from 90' to 135' where it is perfect. Also it improves to perfect at 90' when cooled.

I know about poisoned LCD panels, the ones that turn black due to LCD constituents decomposing.

But what is cold effect due to ?

    Could it be a failing component on the board, capacitor solder connection oxidizing due to age. The connection might improve due to expanding materials as a result of the cold temperatures.

    Is it a polarizing film decomposition?

    Is it decomposition of the LCD component.

So, what is cold effect and can it be reversed.

Any one experimented with other early Seiko panels? Any one have a spare panel :?: :?: :?:

Here is a link to the watch in question: http://www.newdwf.com/viewtopic.php?f=58&t=8509

Cheers, Geoff
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Old Tom

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Re: Lcd cold effect?

Post04 May 2017, 17:30

My tuppence worth as no one else seems to what to have a go! The liquid crystal (LC) state exists for a fairly narrow band of temperatures (in early LC materials) and this band seems to narrow as the material ages (your 0624 is 40 years old which is just about the oldest LC material around), The transition point from the LC state to the liquid state also seems to reduce with age and what I think has happened in your display is that some of the material has decayed into a lower transition point material (which has no nematic properties- doesn't twist the plane of the incident light) so that at normal temperatures only part of the material is LC and affecting light passing through. As you cool the panel the "decayed" liquid material transitions back to the LC state and the contrast ratio improves greatly as now all the material is LC and acting on the light passing through. The reason the display appears normal when viewed off axis is probably due to polarisation by reflection (the Brewster angle) coming into play and rendering the top polariser a "super" polariser increasing the apparent contrast ratio.
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767Geoff

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Re: Lcd cold effect?

Post04 May 2017, 18:33

Tom, wonderful explanation on the dynamics of the variability in decaying LCD material.

So back to designing the mini fridge. In the winter I will wear the watch outside the jacket :nikolaus:

I think that explanation is worth a thruppence however :!:

Truly, thanks for the explanation.



Geoff
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Kasper

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Re: Lcd cold effect?

Post06 May 2017, 10:05

Great explanation there Tom. :mega:

The reason the display appears normal when viewed off axis is probably due to polarisation by reflection (the Brewster angle) coming into play and rendering the top polariser a "super" polariser increasing the apparent contrast ratio.
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