Canon iR7086 Series Service Manual page 520

Chapter 14
a. Outline
If image faults occur, it is important to find out whether the cause is in the
latent static image formation block (including the photosensitive drum and
the potential control system) or it is in the developing/transfer system, requir-
ing a check on the surface potential. (You can check the surface potential in
service mode.)
b. Disabling the Auto Control Mechanisms
As a way of checking the mechanisms used for corona current control, lamp
intensity control, or developing bias control, you may disable the auto con-
trol mechanisms (hereafter, non-auto control mode).
As a first-aid measure when a fault exists in the auto control mechanism, you
may use non-auto control mode; keep in mind that all outputs in non-auto
control mode are fixed to standard values.
1. Procedure
1) Make the following selections in service mode, and enter '0':
COPIER > OPTION > BODY > PO-CNT.
2) Press the Reset key twice.
In non-auto control mode, all settings used for coronal current control, inten-
sity control, developing bias control will be set to standard settings stored in
ROM.
2. Making Use of Non-Auto Control Mode
If a fault occurs in images, use the mode to find out if the cause is on the input
side or output side of the microprocessor on the DC controller PCB.
In non-auto control mode, if the fault is corrected somewhat, you may sus-
pect the potential measurement unit or the DC controller PCB.
c. Zero-Level Check
One way of finding out if the surface potential control circuit is good or not
is to use a zero-level check.
MEMO:
A zero-level check is made to see if the microprocessor registers 0 V when
the surface potential of the drum is 0 V.
Using the result of the check, you can find out if the microprocessor on the
DC controller PCB or the measurement unit is good or not; a zero-level
check may take either of the following two methods:
1. Method 1
1) Turn off the power switch.
2) Short the connectors J522-1 and -2 on the DC controller PCB with a
jumper wire, and disconnect the connector J3 of the potential control
PCB.
J522
3) Fit the door switch actuator into the door switch assembly, and turn on the
power switch.
4) Make the following selections in service mode, and check to see if the
reading is between 0 and 30 during initial rotation: COPIER> DISPLAY>
DPOT> DPOT-K.
MEMO:
If the reading is not as indicated, you may 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 PCB.
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.
14-20
Connector J3
F-14-41
4) Remove the 2 screws [1], and detach the potential sensor support plate [2].
5) Put back the developing assembly and the process unit.
6) Connect the connector [1] of the potential sensor.
7) Fit the potential sensor checker electrode (FY9-3041) [2] to the potential
sensor [1].
When fitting the checker electrode to the potential sensor, be sure that the
magnet of the checker electrode will not come into contact with the potential
sensor cover.
[2]
8) Connect the cable [1] of the potential sensor checker electrode to the
frame (GND) [2] of the machine.
Never bring the clip into contact with the sensor cover. Be sure to keep it ful-
ly away from the sensor window.
[1]
F-14-42
[1]
[2]
F-14-43
[1]
F-14-44
[1]
F-14-45