Ricoh FT7770 Service Manual page 60

30
April, '89
CHARGE
1. Corona Unit
This copier uses a dual wire corotron and a highly sensitive selenium drum.
The corona wires generate a corona of positive ions when the charge power
pack applies a high positive voltage.
receives a uniform positive charge (about +800 V) as it rotates past the
corona unit.
A dual wire corotron is used instead of a single wire type because the
highly sensitive drum requires a very uniform charge. The wires are made
of tungsten and have a carbon coating.
The selenium surface of the drum
2-4