HP 48 HG Calculator LCD Screen

[hibiki]

The same happened to my HP48GX (and HP32SII and HP42S). I think it is the reflective pelicule in the back of the LCD. I could repair one of my HP32SII simply replacing the reflective pelicule (adhesive) with an aluminized pelicule from another damaged LCD. Maybe even a white paper sheet could work. The glue in the last layer (the reflective pelicule) decays with heat and time and makes the display dark. The glue should be cleaned from the LCD. Worths a try. I have not dissassembled my other calcs with the same problem, but someday ...
See the same problem in a multimeter display:
https://youtu.be/yZq2w5EHRNg