Please check the following points:

• Make sure you use paper that meets the recommended specifications. To see what kind of paper you can use, click here.
• Check the printer's environment - high temperatures and high humidity can increase the amount of background shading.
• Clean the corona wire. To see how to clean the corona wire, click here.
• Use a new toner cartridge. To see how to replace the toner cartridge, click here.
• Use a new drum unit. To see how to replace the drum unit, click here.