Casio Celviano AP-3 (1990 Vintage)

Bought this new in 1990 or 91. (I think). It's been a great piano. Recently, the speakers have been sounding fuzzy, and I want to check them out, but I can't get the top or sides off to take a look. I've taken out all the screws I can, but nothing budges. Any ideas? Thanks for your help

https://preview.redd.it/tlm0iv1f2xjg1.jpg?width=4032&format=pjpg&auto=webp&s=e42376bda087939d5154f2130939217e37d1cca6

https://preview.redd.it/dgsldu1f2xjg1.jpg?width=4032&format=pjpg&auto=webp&s=1fa54f425a4a264c3ffa6de8a259cd3ad20f9490

https://preview.redd.it/vxokxc2f2xjg1.jpg?width=4032&format=pjpg&auto=webp&s=ff45459052611588751c61b8a09f4427dcf9e332