MY LETTERS ARE NOW DOTS ON OLDER TI AND ROLODEX HANDHELDS? ANY FIX?

Hello there. I have an older Texas Instrument and Rolodex Electronics Handhelds Organizers. They come on and work. However the letters are mostly dots and the letters have disappeared and are mostly dots now. Is there a way to fix this issue on the LCD screen? Do I have to open up the machine? What is causing this issue? Please write back. Thank you.