Please check the following points:

• Make sure you use paper that meets our specifications. Rough-surfaced paper, paper that has absorbed moisture, or thick paper can cause this problem. 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.
• Make sure that you choose the appropriate Media Type in the printer driver.
• Clean the corona wire. To see how to clean the corona wire, clich here.
• The drum unit may be damaged. Put in a new drum unit. To see how to replace the drum unit, click here.