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.

Main motor

DCM

Roller

701

engaging

clutch

CL2

Roller engaging

detection gear

Roller