Hello everyone. I've been collecting calculators for a while now, but I've encountered an issue. Over time, some of them develop a dark spot in the center of the screen, which eventually spreads across the entire display. Others have screens that become rough and hard to read, almost like they're sweating a viscous liquid. Any idea what might be causing this? And, more importantly, what recommendations do you have for storing calculators?
All LCD displays eventually fail. Storage in a cool dry place can help extend the life of a given calculator display. Most responses to a failing display is to replace it with a newer display from an identical or compatible donor. Naturally this involves disassembling one or both calculators that weren't designed to do so.
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Many older LCDs will develop leaks between the two pieces of glass which results in dark spots that look like ink. Eventually it will cover the whole surface. There are some replacement LCDS made for certain Sharp calculators/pocket computers now.
The polarizer film can also darken and detach from the front and/or back surface of the glass. The front polarizer failure tends to look like a cloudy patch starting in the middle and spreading out. The rear polarizer also has a silver reflective backing which can sperate and/or get lots of small black spots on it. You can obtain new polarizing films, but they can be a bit tricky to put on.
https://polarizingsheet.com/lcd-polarizing-sheet.php
Thank you for your answers. The truth is that the situation makes me very sad, everything has happened in less than a year. Quite a few calculators have been ruined (the entire TI 80-86 graphic series for example). And I'm afraid that the HP Voyager series will follow, for example. I attach some photos.
this looks like something else happened, such as way too much heat around the location where the devices were stored
These do appear to be polarizing film failures as Jeff described. Exposure to heat can accelerate this natural decay process. Direct sunlight for example. Having a number of different displays fail in the same period suggests an environment problem where they are kept or stored.
I don't know about the Casios but the HPs can be opened and their displays replaced with donors. Quite a task though.
From reports of similar failures, high humidity is also a significant factor leading to these large dark areas. I don't believe the darkening can be reversed, but storing some desiccant packets with your devices may help to slow the spread.