Canon CR-55 - Manual (Page 52)

48 Regular Maintenance
Sensor Glass
4
Use a commercially available cotton swab to gently wipe dirt off of the sensor
glass.
There are two sensor glass areas, one on each side. Use a cotton swab to wipe
dirt from the entire surface of each.
IMPORTANT
Scratches on the sensor glass may cause marks on the images and could
cause feeding errors. If there are scratches on the sensor glass, contact your
local authorized Canon dealer or service representative.
5
Gently close the reading unit until it clicks into place.
6
Gently close the maintenance cover until it clicks into place.