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LCD display splotches
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floobydust:
These are reflective 7-segment LCD displays that are showing this abberration as a splotch from the center. It seems to get worse with age. Does anyone know what causes this?

I thought the LCD fluid is only where the segments are and the displays work so it's not the fluid.
Looking at the display using a polarized filter at different orientations doesn't show anything matching the splotch, it's either all black or the same as using no filter. I thought the polarizers might be causing it.
The LCD sandwich is an aluminum backing and two layers of glass glued together, and a plastic polarizing film on the front. Made by AND Japan.

During a heat wave this summer, maybe 30°C an ANENG AN8008 display showed the same pattern  :o But it went away when things cooled down. Doubt they're usable in hot weather lol. This is what had me puzzled what is going on with LCD displays.
james_s:
I thought the fluid filled the entire gap between the glass sheets and the segments are defined by the transparent electrodes? Certainly in the case of dot matrix displays I can't see how you'd ever keep the fluid contained in the individual pixels, I had assumed segmented displays worked the same way.
Benta:

--- Quote from: james_s on September 05, 2021, 06:17:59 pm ---I thought the fluid filled the entire gap between the glass sheets and the segments are defined by the transparent electrodes? Certainly in the case of dot matrix displays I can't see how you'd ever keep the fluid contained in the individual pixels, I had assumed segmented displays worked the same way.

--- End quote ---

I'm with you here. The two glass plates are separated by a distance foil around the circumference, the fluid is fully between the plates.
The failure mode here points towards temperature flexing of the plates, perhaps aggravated by atmospheric pressure change, or mechanical pressure on the surface.

Gyro:
Yes, it's uneven spacing between the glass sheets. The LCD has to be able to do a 90' shift in light polarisation so that light can make it through (and back) the crossed polariser films front and back.

A variation in thickness of the liquid crystal film (or energising the segments) interferes with this, causing darkening.

I don't know of any way of de-stressing the glass layers if it's not caused by mechanical pressure in the first place.


P.S. I doubt you'd be able to see anything using an external polariser because what's happening is between the two existing layers on the display.
floobydust:
Thought maybe it's the glass "flowing" with age? The weakest part of the display is the center.
Squishing it can make the LCD segments darken but has no effect on the splotch. Freezing it just seems to have made it worse, one segment was dead (thought zebra strip) and there is now discolouration around it. It might be a chemical reaction between the fluid and electrode. These displays have never been heated up.
I was wrong about the construction, apparently it's an even pour across an entire display, one big pool.
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