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.
  Please refer to the instructions, "How do I replace the toner cartridge?".
  
  
• Shake the toner cartridges gently from side to side.
  
  
• Make sure that the drum unit is installed properly.
  Please refer to the instructions, "How do I replace the drum unit?".
  
  
• Make sure that you use paper that meets our specifications. A rough surfaced paper or thick print media can cause the problem.
  Please refer to "What is the recommended paper?".
  
  
• Clean the laser scanner windows with a soft cloth.
  Please refer to the instructions, "How do I clean the laser scanner windows?".
  
  
• The drum unit may be damaged. Put in a new drum unit.
  Please refer to the instructions, "How do I replace the drum unit?".