Please check the following points:

• Clean the primary corona wire inside the drum unit by sliding the blue tab. To see how to clean the corona wire of the drum unit, click here.
• Make sure the primary corona wire cleaner is at the home position.
• The toner cartridge may be damaged. Put in a new toner cartridge. To see how to replace the toner cartridge, click here.
• The drum unit may be damaged. Put in a new drum unit. To see how to replace the drum unit, click here.
• The fuser unit may be smudged. Call your dealer or Brother Customer Service.