Canon GP335 Service Manual page 464

CHAPTER 14 TROUBLESHOOTING
12 The copy has white spots (horizontal).
Cause
Exposure system
Developing
assembly
Drum unit
Paper
Transfer charging
assembly
Developing bias
Dust-proofing
glass
14-46
Step Check
1 Generate a halftone test print in
service mode. Enter '4' to
COPIER>PG>TYPE. Are there
black lines on the output?
2 Is the problem noted at intervals of
about 35 mm?
3 Is the problem noted at intervals of
about 94 mm?
4 Try fresh paper. Is the problem
corrected?
5 Are there white spots on the
photosensitive drum during
copying operation?
6
7 Clean the dust-proofing glass. Is
the problem corrected?
COPYRIGHT © 1999 CANON INC. CANON 405/335 REV.0 JAN. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
Yes/No Action
NO Go to step 4.
YES • Clean the developing
rolls.
• Dry wipe the surface
of the developing
cylinder.
• If there are scratches
on the surface of the
developing cylinder,
replace the developing
cylinder.
YES • Clean the drum.
• If there are scratches
on the surface of the
drum, replace the
drum unit.
YES The paper may be moist.
Instruct the user on the
correct method of
storing paper.
NO Check the transfer
charging assembly for
leakage.
YES Check the developing
bias.
YES End.