Oce 3121 Technical & Service Manual page 256

Cleaning Bias
As the machine uses direct transfer, toner from the OPC could stick to the
transfer roller (because of a jam). To counteract this, a negative voltage is ap-
plied. This returns the toner from the transfer roller to the OPC:
During the initial rotation, after a press on the Copy button.
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During a part of the last rotation.
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During a roller cleaning, initiated in user mode 'adjustment and cleaning'. In
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this case, the charging roller is cleaned at the same time.
Reference Bias
At times, the transfer efficiency varies. This is due to changes in the environ-
ment or changes in the resistance of the charging roller. To prevent loss of im-
age quality due to such variations, a correction is made to the level of the
voltage to the transfer roller.
The reference bias is applied each time the copy button is pressed. Thus cor-
recting the voltage level.
Sheet-to-Sheet Distance
During copying runs, the bias value is decreased. This is to prevent adhesion
of toner to the transfer roller between sheets of copy paper.
Main power
switch ON
SLEEP
Main motor (M1)
Cleaning bias
Reference bias
Sheet-to-sheet bias
Transfer bias
ed.1
Control power Copy Start
switch ON key ON
STBY
INTR SCFW
SCFW
LSTR STBY
06 Transfer 503