When browsing eBay, you may encounter a TI-85 or two exhibiting a dark spot in the middle of the screen. That was also the case with a TI-85 from my collection. The issue is quite similar to one that plagues Game Boy handhelds, in which the polarizer begins delaminating from the rest of the LCD assembly. For the unit on the left, I peeled off the decaying polarizer sheet, carefully removed any residue using isopropanol, and applied a new adhesive polarizer sheet:
The camera perhaps does it a bit too much justice: the pixels are a nice, solid black like in later calculators, but the background is tinted pea soup yellow. Nevertheless an improvement over what was. It's also possible to apply the polarizer at a different angle for a white-on-black display, but the shadows from the dark areas end up making the lighter text hard to read.
The high-contrast black-on-white of the TI-83 and later calculators was achieved by adding a compensating film just under the polarizer, a design known to the industry as FSTN, in contrast to STN used on the 82 and 85, or TN used on the 80 and 81. Loose sheets of FSTN polarizing film is hard to come by, but some people have had luck using packing tape or cling wrap as the compensating film. My initial experiments got my hopes up until I peeled off the adhesive backing sheet from the polarizing film I had on hand. Turns out, that itself is also a sort of compensating film and without it, there was no angle at which I could replicate the FSTN effect. Between the bubbles in the homemade compensation film, the dark tint of the adhesive backing, and two hours of twisting the polarizer and screen around, I didn't pursue it further.
The camera perhaps does it a bit too much justice: the pixels are a nice, solid black like in later calculators, but the background is tinted pea soup yellow. Nevertheless an improvement over what was. It's also possible to apply the polarizer at a different angle for a white-on-black display, but the shadows from the dark areas end up making the lighter text hard to read.
The high-contrast black-on-white of the TI-83 and later calculators was achieved by adding a compensating film just under the polarizer, a design known to the industry as FSTN, in contrast to STN used on the 82 and 85, or TN used on the 80 and 81. Loose sheets of FSTN polarizing film is hard to come by, but some people have had luck using packing tape or cling wrap as the compensating film. My initial experiments got my hopes up until I peeled off the adhesive backing sheet from the polarizing film I had on hand. Turns out, that itself is also a sort of compensating film and without it, there was no angle at which I could replicate the FSTN effect. Between the bubbles in the homemade compensation film, the dark tint of the adhesive backing, and two hours of twisting the polarizer and screen around, I didn't pursue it further.
