blackened lcd display



#2

hi, just a question for the forum gurus: i have a number
of hp calculators with lcd displays, some segmented as the voyagers' or the 41, others dot-matrix type, as the 71b's for instance, and they never developed any stains or defects with age

however, i recently got an old sharp (not hp) basic pocket computer which has an lcd display much like the 71b's, only with yellow background, and though the machine seems completely new, no dents or other signs of physical abuse at all, the display has large blackened areas throughout,
mostly by the upper and lower edges. they appear to cover every part of the display, save the dots themselves or the indicators (deg, rad, run, pro, ...)

despite those darkened areas, the lcd display is completely functional if hard to read. my question is: what could have caused such dark zones ? i think that any stress or condition serious enough to cause them should have also caused the display to fail completely or at least would have left physical marks.

also, can this condition be cured somehow, such that the dark zones dissappear ? i tried to let the machine on running some program continuously just in case this could do any good but to no avail. thanx.


#3

I think the yellow filter was used because early LCD panels were damaged by (uv?) light. It could be that your Sharp calc has suffered from too much exposure to sunlight.

I don't now of a cure - I would suspect that it is not possible and is due to the age of the device {:^(

I have seen some of the higher model early Sharp pocket 'PC' calcs and was impressed at the time (at uni).

HP's LCD's seem to hold up much better and never needed a yellow filter - is this because HP held back from rushing out an LCD model until the technology was better??? (If so well done HP).

Tom.

#4

Which SHARP basic pocket computer?


#5

it's a sharp pc-1211 (aka radio shack's trs-80 pocket
computer). it has an lcd display with a yellow background
instead of the later grey background used in the pc-1212,
1500, 1500a, etc.

the funny thing is, the machine works, and the display works too, only the lcd display has very dark zones
everywhere except in the dot matrix zone and the deg, rad, etc indicators so you can actually read the characters
displayed but it's very annoying with all that
black rubbish around them.

really, i can't understand what kind of fault or accident
can damage all zones except the dots and indicators
themselves. perhaps it's even easy to correct, if one knows how ...


#6

I've got the exact same model. I've had it from new and it's still in my desk. Its display is flawless, but it's lived its life in the hard case inside a drawer, so perhaps there's some truth to the UV theory.

#7

LCD's display (i.e. become dark) by having current flowing through the elements. This must be ac (alternating current) as a dc voltage damages the display.

The back plane of the LCD is normally connected to an alternating voltage and the elements to be made dark have the oposite polarity applied.

To make the elements clear the same alternating voltage as the back plane is applied (i.e. no voltage difference accross the element = clear)

I don't know the construction method of the early Sharp LCD's or how thay become damaged (if at all) by uv light.

Perhaps the display has been damaged by uv but the elements that have ac accross them have 'recovered' by electro - chemical action. The 'un-used' parts of the display never have current passing through them so may never 'recover'.

The above is and educated guess - I'm not an LCD expert.


#8

tom; i've seen two of these and they had a "bleeding black in from the edges" kind of look like possibly the screen was delaminating. when the black touches an active part of the display it seems to deactivate that segment.
it's the same on or off. i believe that the black keeps creeping inward on all fronts till it joins the displays active area. btw: one was a ti 1750 yellow lcd display. the yellow is said to be a filter that was used until they could make a uv stable lcd. the other one was a 41 fullnut that got closed in a truck tailgate. they both still calculated but did not display very well. - d


#9

I saw this on a semi-recent Casio machine (fx9900GC), which was carefully stored away from the sun. To my surprise, the darkened area was almost gone the next time I took a look at it. So the problem is not necessarily linked to UVs (but the old-tech LCD of the PC1211 may be more prone to UV damaging).
Also, there might be some "healing" action from use.
I saw also this phenomenon on a Psion 3 years ago, but the spot never disappeared. As a matter of fact, the dark area looked as if it was -below- the LCD elements, which were still active. Strange ?

With years passing we will be probably be running into such weird problems with the more recent machines which were not built to last like the expensive first generation LED beasties. This is frightening.


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