Canon LaserBase MF8180C, Service Manual

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Chapter 2
2-29
F-2-43
2.3.7.3 Secondary Roller Position Detection
0008-1719
This printer has a function of detecting the engaging position of the secondary transfer roller between the roller and ITB.
The home position of the roller is detected by the DCNT Board monitoring the roller engaging sensor (PS714) and FEEDBACK (TR2S) signal for the secondary
bias.
The DCNT Board detects whether the roller is at its home position (Note) when the power is turned on or the top cover is closed. This detection is performed by a
flag located at the end of the engaging detection gear interrupting the PS714. When the roller is at its home position, the PS714 outputs "L".
When the engaging detection gear is not at its home position; the PS714 is "H", the DCNT Board rotates the main motor and let in the roller engaging clutch (CL2)
for a specified period to return the gear to its home position.
Then the DCNT Board detects the position of the secondary transfer roller, engaging and disengaging, by monitoring the FEEDBACK (TR2S) signal for the sec-
ondary transfer bias.
When the roller is at its engaging position, the resistance of the roller increases and the value of the TR2S signal decreases since the roller contacts with the ITB.
When the roller is at a disengaging position, the resistance decreases and the value increases.
If the value of the TR2S signal does not vary when the CL2 is on, the DCNT Board stops the printer engine and notifies a secondary transfer roller engaging mech-
anism abnormality to the SCNT Board.
The home position for the secondary transfer roller is the state in which it is disengaged from the ITB.
Engaging lever
Secondary
transfer roller
DCNT Board
Main motor
Roller
engaging
clutch
Roller engaging
detection gear
Engaging cam
ITB
<Engaging> <Disengaging>
Roller
engaging
sensor
Engaging cam
Secondary
transfer roller
Engaging lever
ICLRSNS
/TR2CLD
PS714
DCM
701
CL2