Gestetner B147, Service Manual

Page: 511 / 1081

PHOTOCONDUCTOR UNIT
SM 6-53 B147/B149/B190
Detailed
Des
cription
s
6.7.4 DRUM CHARGE AND QUENCHING
This machine uses a non-contact charge roller [A] to reduce ozone. The non-
contact charge roller gives the drum surface a negative charge. The high voltage
supply board – C, B, which is located at the rear of the machine, applies a dc and
ac voltage (at a constant current) to the roller. The ac voltage helps to ensure that
the charge given to the drum is as uniform as possible.
The machine automatically controls the charge roller voltage if automatic process
control is enabled (i.e., if SP3-125-1 is set to 0). However, if process control is
switched off, (i.e., if SP3-125-1 is set to 1), the dc voltage is the value stored in
SP2-001-1 to -9 (do not adjust in the field unless advised to do so).
The diameter of the roller is 11.14 mm (circumference about 35 mm). The gap
between a drum and the corresponding charge roller is about 50
µ
m.
The cleaning brush roller [B], which always contacts the charge roller, cleans the
charge roller.
The charge roller can generate small amounts of nitrogen oxide gases (known as
NOx), which may be absorbed by the surface of the drum. This can cause
unfocused copies. To avoid this, the film of NOx is removed at power on, at the end
of a job (if more than 200 prints), and when a toner cartridge has been replaced.
SP3-920-1 to -4 determine when this procedure (known as “refresh mode”) is done.
It can also be executed at any time (using SP3-920-5) if the prints are smeared.
Quenching is done by illuminating the whole area of the drum with the laser at the
end of every job.
B146D531.WMF
[A]
[B]