Canon CP660 Service Manual page 277

Work as follows:
Item
Density sensor
Pre-exposure LED
assembly
Registration roller
assembly
COPYRIGHT © 1999 CANON INC.
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Use the density sensor cleaning brush attached to the printer unit to
clean the detecting window of the sensor. For the pre-exposure LED
assembly, move the same brush in the direction of the arrow to clean
each LED.
When replacing each drum cartridge, clean the registration roller
assembly.
CANON 660/2100 REV.0 FEB. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
CHAPTER 9 MAINTENANCE AND SERVICING
Description
Cleaning brush
Detecting
window
9-3