Canon ImageRunner iR8500 Series, Service Manual, Page: 696 / 1122

Chapter 14
14-42
14.7.17 Checking the Surface Potential Control
System
0008-8472
/ iR8070
a. Outline
If an image fault occurs, it is important to find out if the cause is in the
latent image formation block (including the photosensitive drum and the
potential control system) or in the development/transfer system,
requiring a check to see if the surface potential is appropriate.
The service potential may be checked in service mode.
b. Disabling Auto Control
As a means of finding out if the corona current control, lamp intensity
control, or developing bias control mechanisms is faulty, the auto
control mechanism may be disabled
(hereafter, "non-auto control mode").
In addition, non-auto control mode may be made use of as an emergency
remedy in the event a fault occurs in the auto control mechanism.
[1] Procedure
1) Make the following selections in service mode, and enter '0':
COPIER>OPTION>BODY>P0-CNT; then, press the OK key.
2) Press the reset key twice.
When non-auto control mode is selected, all settings for corona current
control, intensity control, and developing bias control will automatically
be set to standard settings stored in ROM.
[2] Making Use of Non-Auto Control Mode
Use it to find out if the cause is on the input side or on the output side of
the microprocessor on the DC controller PCB when an image fault
occurs.
If any improvement is noted in non-auto control mode, a fault may be
suspected in the potential measurement unit or the DC controller PCB.
c. Zero-Level Check
A "zero-level check" may be used as a means to find out whether the
surface potential control circuit is good or not.
REF:
In a zero-level check, a check is made to find out whether the
microprocessor indicates 0 V when the drum surface potential is 0 V.
Using a zero-level check, the microprocessor on the DC control PCB
and the measurement unit may be checked.
In method 1, the condition of the level shift circuit on the DC controller
PCB may be checked while in method 2 the potential control circuit may
be checked.
[1] Method 1
1) Turn off the power switch.
2) Short J522-1 and -2 on the DC controller PCB with a jumper wire, and
disconnect connector J3 of the potential control PCB.
F-14-101
3) Fit the door switch actuator in the door switch assembly, and turn on
the power switch.
4) Make the following selections in service mode
(COPIER>DISPLAY>DPOT> DPOTK ), and check to see that the
reading of initial rotation is between 0 and 30.
MEMO: If not, suspect a fault in the DC controller PCB.
5) Turn off the power switch, and detach the door switch actuator.
6) Detach the jumper wire from the DC controller PCB.
7) Connect the connector to J3 of the potential control circuit.
8) Turn on the power switch.
[2] Method 2
1) Turn off the power switch.
2) Remove the developing assembly, and slide out the process unit.
3) Disconnect the connector [1] of the potential sensor.
F-14-102
4) Remove the two screws [1], and detach the potential sensor support
plate [2].
F-14-103
5) Put the developing assembly and the process unit back to their
original positions.
6) Connect the connector [1] of the potential sensor.
F-14-104
7) Fit the potential sensor checking electrode (FY9-3041) [2] to the
potential sensor [1].
When fitting the checking electrode to the potential sensor, take care so
that the magnet of the checking electrode will not come into contact with
the potential sensor cover.
Connector (J3)
J522
J522
[1]
[2]
[1]
[1]