Sharp SF-7320 produces grainy copies

This means the machine is over-toning ie using more toner than required caused by either improper toner or different brand of toner. The correct toner is sf 222T1. Replace developer and use the right toner and clean the drum and its blade. You may need to clean fuser rollers for cleaner copies.

Replace the copying clutch or clean the reverse copy clutch and clean and oil the scanner rail.

Check the copy lamp and its thermal fuse if they are okay, then clean optics, check drum and blade and clean or replace and finally clean or replace fuser rollers. If the above is ok and still black copies, check the copy lamp wire harness for continuity or the copy control board located underneath the display panel and check for bad component like triac and replace. If OK replace the main control board.

Check copy lamp if its lighting during copying if not Switch off and remove socket outlet and check lamp and thermal fuse . Clean optics.

There are several solutions to this problem:
1. Adjust the exposure
2. The drum may be out.
3. The developer may be out.
4. Finally, You may need a PM for the copier. (replace the drum, developer, drum blade)

Also adjust your front door which acts as a switch.

Check the heat roller and clean or replace.

Sound like you need to have the developer, drum and drum blade replaced, you might want to have a tech look at this.
Hope that helps.
Lbcoaster

check if the developer that comes in a silver bag has been installed and the screw that fastens the scanner has been removed.

This means the developer unit is not installed . Check and instal.