I searched and found many repair options for the C33 radios (mine is in a 1996 328i) out there that are dim. I have not found any on corrections for all the pixels lit up. I can push on the screen lightly and see the text. I looked in the the coding menu but there is no adjustment in coding for this radio version. The one funny thing I found was 3 radio code cards in the owners manual so it appears it has been replaced many times already.

Thanks,