Help with a general LCD problem in HP 11C (Voyager series)



#4

A colleague gave me an 11C that he had stored for many years in a vertical position. This seems to have caused the display to have developed an irregular black stain along the top edge. The stain/blotch is present whether the calculator is on or not. It appears as if some of the liquid material in the display migrated down to the low side to create this stain. The calculator, including the display, is still fully functional and the stain does not extend into the area of the display where the numbers are displayed. Is there a way to reduce the size of the stain, such as storing it vertically in the other direction? Or will this only cause the stain to move down into the number part of the display and ruin what is currently a functional, if ugly, situation? Please post a response here and/or email me at c_j_falk@yahoo.com. Thanks in advance for any help.


#5

Hi Chris,

Sorry about the bad news, but there isn't such a cure for LCD's "seal broken" desease.

What has been repeatedly described a number of times in this forum as: "stains", "worm paths", "hair lines", (and a very interesting set of the most ingenuous descriptions) is nothing but air.

Originally, LCD displays are sealed, containing a very small amount of "liquid crystal" between two glasses. Transparent conductive electrodes (made of an Indium salt compuond IICR) are etched on the inner surface of both glases.

Most of LCD's used in calculators use the transflective method and twisted nematic Liquid Crystal, requiring a reflective surface back layer behind the bottom glass. The reflected light is polarized and this polarization must be "twisted" by the crystals.

On top of the upper glass all LCD's are covered by a polarised filter. Reflected polarized light comming from the back panel will pass thru the crystals if the segment is not "active".

In fact what we "see" as an *ON* segment is usually the segment which polarisation (produced by the electrodes) blocks the path of light, by twisting its crystals in the opposite direction to which the polarized upper filter is oriented.

When shock, vibration or just *age* damages the sealing, a small portion of air find its path between the glasses. Of course, air does not twist the light in any way so it cannot pass thru the filter, thus the *black* stain.

Hope this claryfies the issue, and sorry not being of much help.

Diego.


#6

On the contrary, you were of great help in understanding the problem and saving me from wasting my time trying to fix it. I'll just enjoy the calculator for what it is... a backup for the HP 15C that I use everyday. Thank you for such a complete explanation. I did search the forum first to try and avoid asking a question with an obvious answer, but I'm new here and must have used some bad search variables. The entries I found only talked about the worm-like lines that I though was a separate problem. Thanks again.


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