Canon NP6251 Service Manual page 603

CHAPTER 11 TROUBLESHOOTING
4. The copy has an uneven density (darker at front).
5. The copy has an uneven density (lighter at front).
Cause Step
Primary
charging wire
Developing
assembly
Scanner
Pre-exposure
lamp
Developing
assembly
Charging
assembly, Copy
paper
11-72
COPYRIGHT © 1997 CANON INC.
Checks
1 Perform the Image Adjustment
Basic Procedure. Is the problem
corrected?
2 Are the developing rolls of the
developing assembly firmly in con-
tact with the photosensitive drum?
3 Clean the scanning lamp,
reflecting plate, side reflecting
plate, mirror, lens, dust-proofing
glass, and heat absorbing glass.
Is the problem corrected?
4 Is the pre-exposure lamp flashing
during copying?
5 Is the developing cylinder coated
with an even layer of toner?
YES/NO
YES
NO
YES
NO
NO
YES
CANON NP6350/NP6251 REV. 0 JULY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)
Action
End.
Check the developing
assembly locking unit.
End.
1. Replace the pre-
exposure lamp.
2. Replace the DC
controller PCB.
1. Clean the tip of the
blade of the
developing assembly
(dry wiping).
2. Clean the surface of
the developing
cylinder.
3. Check the toner inside
the developing
assembly to see if it is
level.
1. Clean all charging
wires once again, and
check their height.
2. Try replacing copy
paper.