The Copy Is Too Light - Canon NP7160 Service Manual

CHAPTER 10 TROUBLESHOOTING
2. The copy is too light. (including solid black area)
3. The copy is too light. (entirely, considerably)
Cause Step
Transfer
charging
assembly
Copy paper
Lower transfer
guide/varistor
High-voltage
cord, DC
controller PCB
Developing
assembly
Toner sensor
(TS1)
Photosensitive
drum
Developing
bias control
10–30
COPYRIGHT © 1998 CANON INC.
Checks
1
Perform the Image Adjustment Basic
Procedure. Is the problem corrected?
2
Turn off the power switch in the
middle of copying operation. Then,
open the front door, and open the top
unit. Is the toner image on the
photosensitive drum before transfer
more or less normal?
3
Is the charging wire of the transfer
charging assembly hooked correctly?
Are its height and position normal?
4
Is the transfer charging assembly set
securely?
5
Try paper fresh out of package. Is the
problem corrected?
6
Measure the resistance between the
lower transfer guide and the metal
portion of the feeding assembly. Is it
0 ?
7
Is the developing assembly set
securely? Are the rolls of the
developing assembly firmly in
contact with the photosensitive drum?
8
Is toner in the developing assembly?
9
Replace the drum unit. Is the problem
corrected?
Yes/No
YES
NO
NO
NO
YES
YES
NO
NO
NO
YES
NO
CANON NP7161/NP7160 REV.0 AUG. 1998 PRINTED IN JAPAN (IMPRIME AU JAPON)
Actions
End.
Go to step 7.
1. Hook the charging wire correctly.
2. Adjust the height of the charging
wire.
1. Clean the charging wire.
2. Set the charging assembly securely.
1. The paper may be moist. Instruct
the user on the correct method of
storing copy paper.
2. Inform the user that the use of
paper of a type not recommended
by Canon may not always bring
about good results.
1. Check to make sure that the
transfer guide is not in contact with
the metal area of the feeding
assembly (e.g., side plate).
2. Replace the varistor.
1. Check the continuity of the high-
voltage cord.
2. Check the high-voltage power
supply (primary/transfer) and the
DC controller PCB.
Check the developing assembly
locking lever.
Check the tone sensor. Then, supply
toner.
End.
Check the control system of the
developing bias.