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Jeff Liebermann Jeff Liebermann is offline
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Default Why dont they seal LCD devices?

On Sun, 17 Mar 2019 00:21:45 -0500, wrote:

I've learned over the years that water destroys all LCD screens.


Wrong. I have devices with LCD screens that are at least 20 years old
that work just fine. Where did you get this "information"?

Several
years ago, I had a pipe break in my house. Did considerable damage to
the house and other stuff, but it soaked a police scanner and a AM FM
radio nearby. The radio had an analog dial. I dried it well, and it
worked fine.


I had to do that for a friend who had a similar flood. I used an air
compressor to blow away most of the water, and plenty of hot air from
a carpet dryer to evaporate the rest.

I dried the scanner too. The scanner turned on, but the LCD screen was
dead.


All black, all clear, segments missing, etc? Dead is not a technical
term.

That rendered the scanner useless. Aside from that, the speaker
was shot. Replacing the speaker was minor, but even if I could find a
replacement LCD, I am sure it would have been costly and difficult to
replace.


Yep, that's usually the problem with custom LCD displays.

Eventually I found an identical scanner on ebay for probably less than
what a replacement LCD would have cost me.


Nicely done.

I lost a cellphone outdoors. Weeks later I found it, after several rain
storms. The same with that. The LCD screen was dead. The phone appeared
to work, (made sounds), but without the screen it was useless.


You keep saying "dead". I can usually tell what killed the display if
you would kindly provide a better description.

I had a similar experience with a GPS, which got soaked.


That could have been saved. The problem is that standing water is
sucked into the display through the pressure relief hole when the
temperature of the panel drops. For example, if you warm up a display
to something above ambient, such as 30C, and then dump it into 12C
water, the liquid and air inside the panel will contract, creating a
partial vacuum, and sucking in the standing water. You can heat up
the panel in the hope that the water remains near the point of entry,
but I haven't had much luck doing that.

What does work is turning the LCD panel upside down. For some dumb
reason, the designers of most (not all) LCD panels put the pressure
relief hole at the bottom of the display. When even splashed with
water, the water will puddle near the bottom of the panel, and
eventually be sucked in by the partial vacuum. Turning the display
upside-down moves the puddle to where it can do less damage. However,
there's a problem. If the panel has a metal frame, as in most laptops
and LCD monitors, the water puddle will be trapped between the glass
panel and the metal frame. I don't have a solution for this
situation, except to turn the panel upside down while drying and hope
for the best. Whatever you do, don't let the panel cool down until
you're sure all the water has been cleared from the pressure relief
hole (with an air compressor).

Why dont they put some silicone sealer on the edges of those LCD
screens? Or something that will prevent water from getting into them?


Because changes in altitude, air pressure, and temperature will cause
the glass panel to either expand or cave in. If thin enough, it will
probably crack. Small changes in air pressure over large panels such
as big LCD monitors will result in quite a few pounds of pressure on
the display. A 0.1 psi change in air pressure, across my 270 sq-in
LCD display, will exert 27 lbs of force over the entire glass area.
Putting that much weight on thin glass will bend and possibly break
it. So, there has to be a method of equalizing the internal pressure
with the external air pressure, which is the pressure relief hole. The
problem is less with small displays, but pressure relief holes are
still used quite often.

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Jeff Liebermann

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