2004 Nissan Sentra speakar not working

Electrical problem
2004 Nissan Sentra

hi,
in my car speakar on left front and rear both are not working at all. setting from the player is ok as well as i believe speakar is ok. i would like to know is their any fuse in the output of each side of speakar or else how can i open originally installed cd player or if you have wiring diagram please share it.

thanks
in advance