White spots or black spots at 94 mm (3.7 in.) intervals

• Make ten copies of a blank, white sheet of paper.
  If the problem is not solved, the drum unit may have glue from a label stuck on the OPC drum surface. Clean the drum unit. Please refer to the instructions, "Clean the drum unit".
  
  
• The drum unit may be damaged. Put in a new drum unit. Please refer to the instructions, "REPLACE DRUM"