Please check the following points:

• Make sure that 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.
• Try a new toner cartridge. To see how to replace the toner cartridge, click here.
• Try a new drum unit. To see how to replace the drum unit, click here.