Remove the cartridge(s) from the printer and clean the metallic drum on the front of the cartridge. Try to rotate the drum to ensure its left clean all the way around
If the printer has a separate image drum or photoconductor unit the most likely cause of image defects other than the toner is the drum. Many laser printers have a maintenance kit, Image drum unit, which includes the fuser, transfer roller and paper pick-ups.
These imaging drum units only have a limited page life and need to be replaced when an image problem occurs.