Canon PC300 Service Manual page 48

2. Operations
Figure 3-19 shows the circuit that con-
trols the developing bias, and the circuit has
the following functions:
¢ Turns the developing bias AC compo-
nent ON and OFF.
¢ Turns the developing bias DC compo-
nent ON and OFF.
* Controls the voltage level of the DC
bias according to the settings made by
the copy density dial/lever.
a. Turning the Developing Bias AC
Component ON and OFF
* ACBTP=0 (pulse output OFF)
T7104 goes OFF.
The above condition deprives the devel-
oping cylinder of the AC bias.
¢ ACBTP=1 (pulse output ON)
T104 goes ON.
The above condition raises the AC bias
output using the high-voltage trans-
former (T104) and sends it to the devel-
oping cylinder.
b. Turning the DC Bias ON and OFF and
Controlling the Voltage Level
The DC bias is turned ON and OFF by
the DC bias control command (DCBPW™).
The microprocessor checks the DC volt-
age when the DC bias is ON so as to keep it
to the specified voltage.
a) DCBPWM-=0 (DC bias OFF)
Q146 goes ON.
DC bias goes OFF.
b) DCBPWM=1 (DC bias ON)
Q146 goes OFF.
DC bias goes ON.
COPYRIGHT © 1994 CANON INC. CANON PC300/320/325,FC210!290 REV.O JULY 1994 PRINTED IN JAPAN {MPRIME AU JAPON)
OPERATIONS AND TIMING fs
The voltage level of the DC bias is con-
trolled by varying the pulse width of the DC
bias control command (DCBPWM).
While the photosensitive drum is rotating
except during development, about -400 V is
applied to the developing cylinder.