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After partially disassembling and re-assembling an old dell Inspiron 1525, I noticed a row of four apparently dead pixels which weren't there before. This row gradually grew to a largish blotch which is visible even when the monitor is off, and doesn't vary with screen brightness:

enter image description here In the first frame the screen is off and illuminated only with an external light source. In the following frames the screen is on and the brightness increased gradually. The camera exposure is constant across all images.

When the above gif was captured the blotch appeared quite dark and opaque. However, sometimes it appears rather "transparent"; i.e. the affected pixels are partially illuminated and content within can be discerned:

enter image description here

What exactly could cause pixels to do this, and what might I have done to initiate it?

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    I'm no expert but it looks like the LCD layer itself is cracked & starting to leak. – Tetsujin Feb 7 '17 at 7:47
  • If it was stable, it could be physical damage to the layer, perhaps caused by the edge of something pressing hard against the screen. The fact that it's getting worse points to leakage. There isn't a reliable or effective way to fix this. Screen replacement is the usual cure. – fixer1234 Mar 27 '17 at 15:27
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A liquid crystal display is made of several layers; one of these is the liquid crystal itself. If the interface breaks, then the Liquid crystal will start to leak out.

How does the interface break?

The interface breaks simply because it made of solid material and as any material it is bound to one day break, two parameters will make it break faster:

  • External stimulations: very ‘hard treatment’ such as sharp objects, shocks. But also long exposure to UV light, heat, or extreme cold.
  • The initial quality of the material: this depends on the material used by the vendor, the inspections performed, and luck.

What happens when it breaks?

Naturally the liquid crystal will leak out; there is not much information about the fluidic properties of the liquid crystal through breaks. We can still note that the focus of liquid crystal materials is mainly the switching speed and therefore the viscosity of the fluid should be reasonably low.

What impact?

For your case, the display is a twisted nematic display. – my reference -

  • If there is no liquid left the light will try to go through two perpendicular polarizer and therefore would be totally obstructed this explain why the pixel are black with (your second picture) or without (your first picture) backlight
  • However if there is still a bit of the liquid left the light polarization can still be partially rotated and therefore a small component can pass through the second filter, this explain why you can still see some contrast.

Is there a way to stop this leakage?

No. The dimensions are too small you will not be able to strip the upper layers or patch without further damaging anything. These are devices made with the help of advanced precision machines.

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