Ricoh A085, Manual

Page: 325 / 617

8.4 AUTOMATIC DRUM CURRENT ADJUSTMENT
This copier has an automatic drum current adjustment circuit for the transfer
and separation corona outputs.
8.4.1 Drum Current Detection
The drum current detection circuit is shown in the above circuit diagram.
The drum current on the drum surface produced by the transfer or the
separation corona output is sent at CN111-A25 of the main board through the
drum front shaft, drum shaft bearing, and drum unit connector. Inside the
IC148 (hybrid IC), the drum current is grounded via the resistor (2 KOhm)
and the voltage produced between both ends of the resistor corresponds to
the amount of the drum current. This voltage is separated into ac and dc
components and these are amplified in the IC148. The amplified components
are sent to the analog input port of IC132 (I/O CPU) and are converted into
an 8 bit digital signal. The I/O CPU detects the drum current from this digital
signal.
Transfer Corona Trigger
Transfer PWM
Separation -DC PWM
Separation -AC PWM
Separation Corona Trigger
11 DR1
2K
VO1
TP111
(I Drum)
IC 148
DAC
DDC
DCPOL
1
2
10
TP106
(Drum-AC)
TP107
(Drum-DC)
41
40
AN7
AN6
TP112
(DCPOL)
15
PC4
IC 138
[I/O Expander]
IC 137
[PWM Timer]
8
9
7
Main Board
IC 132
[I/O CPU]
OPC Drum
[Drum Current]
CN111-A25
CN103-2
CN103-6
CN103-5
CN103-7
CN103-1
T
D
High
Voltage
Supply
- CTBG
High
Voltage
Supply
- D
Data Bus
NV-RAM
[Ram Board]
[Main CPU]
IC 135
IMAGE TRANSFER AND PAPER SEPARATION 12 February 1992
2-70