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Hey, electronics people: A few months ago, I cleaned a spot on an LCD flat screen. Whatever it was, it was stuck on there pretty good and I guess I pushed down on it too hard (actually wasn't hard at all, to be honest). Anyway, next time I turned it on there was a huge blob of dead pixels in and above that spot. It's taken a few months, but the size of the blob has significantly reduced in size and continues to fade.

Here are two images taken less than 24 hours apart. It doesn't usually happen so quickly; I think it was just a lucky coincidence that I happened to take the first photo at the right time. It's still only marginally noticeable, but when it first happened (I'll try to find an older image) all three dead spots were all bridged together as one and the outside edge has gradually receded. First (if you look closely), they tend to go from black, to blue, to cyan (sometimes?), before fading back to normal.

Can anyone explain this? I actually expected the dead spot to do the opposite; slowly grow bigger until the display was rendered useless.

enter image description here

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  • \$\begingroup\$ great question! Many years ago I had an early LCD watch - the strap broke and I fixed it by soldering some wire. In the process the screen went completely black do to the heat. But an hour later it was fine. \$\endgroup\$ – dmb Jun 2 '18 at 9:26
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    \$\begingroup\$ perhaps the pressure squeezed the liquid crystal out from between the sheets and it has to flow back. \$\endgroup\$ – Jasen Jun 2 '18 at 9:59
  • \$\begingroup\$ @Jasen That's what I was thinking, too. If I pushed on the screen of my scooby doo digital watch, the segments get messed up, but a minute or so later it's fine again. Heck, I can push on my laptop screen to see a fun splash of color around my finger tip. I'd guess that pushing too hard would eventually destroy that area. \$\endgroup\$ – Kurt E. Clothier Jun 11 '18 at 18:26
  • \$\begingroup\$ Just an update: The two smaller/thinner blobs are gone now. \$\endgroup\$ – tjt263 Jun 16 '18 at 14:55
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How do LCD screens repair themselves?

I pushed down on it too hard (actually wasn't hard at all, to be honest). Anyway, next time I turned it on there was a huge blob of dead pixels in and above that spot. It's taken a few months, but the size of the blob has significantly reduced in size and continues to fade.

If you push slightly the screen restores itself immediately.

If you push too hard you will damage the screen permanently.

If you press a bit more than a little, but not too much, some of the warmed crystal can squeeze out. Both time and varying electric current twisting the crystal might cause it to return to it's correct location - not something you would want to test on a new screen.


Sources:

ScienceABC - Why Do LCD Screens Produce Ripples When You Put Your Finger On Them?

"The characteristic of liquid crystals that makes them ideal to be used in display screens is that they align themselves when an external electric field is applied to them. To be more technically specific, these liquid crystals are sandwiched between two pieces of polarized glass ...".

Chemistry.SE - Why do liquid crystal displays (LCDs) visually distort under pressure?

"To create a liquid crystal cell, twisted nematic liquid crystal is filled between two crossed polarizers1, and a backlight is sent through. The important thing about liquid crystals is that the specific rotation is easy to control by varying the potential difference (more potential difference leads to more anisotropic disorder).

Now, if you make a grid of these and put color filters on them, we get an RGB LCD display.

What happens when you press on them? You change the concentration/length of the liquid crystal, as well as making it bulge out slightly2.. This changes the optical rotation it induces, causing the amount of light that comes out to change (as the amount of light is dependant on how aligned the rotated light is with the second polarizer) ...".

...

"The persistence is because liquid crystals are viscous — they have to be, as they consist of long molecules. They seem to align quickly to potential differences (potential differences align the molecules without moving the liquid), but when we add pressure (where the liquid itself distorts) I think it takes some time to bounce back. The ripples move due to this same persistence.".

Quora - How do you fix stuck pixels on an LCD TV screen?

"... several people have had good luck simply applying a small amount of pressure to the affected pixel with your finger or a pen through a folded paper towel or piece of cloth (to keep said pen from scratching the screen). While applying pressure, turn the screen on and off several times.".

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