Please check the following points:

• Check that the machine is on a solid level surface.
  
  
• Check that the back cover is closed properly.
  
  
• Check that the toner cartridges are installed properly.
  
  
• Shake the toner cartridges gently.
  
  
• Check that the transfer roller is installed properly.
  
  
• Replace the transfer roller.
  To see how to replace the transfer roller, click here.