Please check the following points:

• Make sure that the machine is on a solid level surface.
• Make sure that the toner cartridges are installed properly.
• Shake the toner cartridges gently.
• Make sure that the drum unit is installed properly.
• Make sure that you use paper that meets our specifications. A rough surfaced paper or thick print media can cause this problem.
• Clean the laser scanner windows with a soft cloth.
• The drum unit may be damaged. Put in a new drum unit.