Sharp AM-900 - Manual (Page 134)

Maintenance
132
3
Close the auto document feeder cover, pressing down on both sides to
make sure it clicks into place.
Cleaning the document glass
Open the document glass cover and clean the document glass by wiping it
with a soft, dry cloth (be sure not to use a cloth that will scratch the glass). If
needed, moisten the cloth with isopropyl alcohol or denatured alcohol.
Press down
on the marks