Ricoh FW 810, Service Manual

Page: 26 / 170

2.2 CHARGE CORONA CIRCUIT
The main power supply board su24 volts (Va) to the charge/bias
power pack as the power supply source. About 8 seconds after the Start key
is pressed, the CPU drops CN107-B14 from +24 volts to 0 volt. This actuates
the dc/dc converter within the power pack which applies a high negative
voltage of approximately --5.3 kV to the charge corona wire. The corona wire
then generates a negative corona charge.
The grid limits the maximum corona charge to --940 volts. This ensures that
the charge does not fluctuate and an even charge is applied to the drum
surface. When developing the test pattern for the image density sensor, the
grid charge is --460 volts.
The copy grid voltage, and ID sensor grid voltage amounts can be adjusted
using service program modes #23 and #22, respectively.
The grid drive signal applied to CN1-6 is a pulse width modulated signal. As
the width of the pulses applied increases, the strength of the grid charge also
increases. The main board monitors the grid charge at CN110-8 and controls
the width of the drive pulses based on this feedback.
Charge / Bias PP
CN1-1
CN1-2
CN1-3
CN1-6
CN1-10
DC Power
-6
-B14
CN110
-8
GND
DC/DC
Main Board
Charge
-1
CN107
CN2
24V Va
Grid Drive
0/5
Grid monitor
Converter
DC/DC
Converter
24
0 2.5
6 January 1990
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