Canon LBP-2000, Service Manual

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2 - 21
CHAPTER 2
b . D e v e l o p m e n t
TB403/TB404 Dv
TB405/TB406 Ant
TNRCHKT
TNRCHKD
/DVACFOT
/DCPWM
/DVDCFOT
To primary bias circuit
To developing
cylinder
From toner level sensor
DC controller PCB
Developing bias circuit
ASIC
CPU
Developing DC
bias voltage
detection circuit
Developing bias
detection circuit
Toner level
detecting circuit
DC generation circuit
AC generating circuit
Comparison
circuit
/DVDCUP
/DVACON
Superimposition
Figure 2-2-11
The ASIC generates the developing AC bias drive signal (/DVACFOT), developing AC bias ON/OFF
signal (/DVACON), developing DC bias drive signal (/DVDCFOT), and primary /developing DC
bias output level signal (/DCPWM), and applies a voltage which is a combination of a developing
AC bias and a developing DC bias to the developing cylinder.
When not forming images, the developing DC bias output switch signal (/DVDCUP) is used to
apply the developing DC bias (with a voltage higher than that used when forming an image) to
prevent soiling of the pressure roller.
The developing DC bias is monitored by the developing DC bias voltage detection circuit, and is
fed back to the DC generation circuit by way of the comparison circuit so that the Printer may
control the voltage of the developing DC bias. The developing DC bias is varied in conjunction with
the voltage of the primary DC bias according to the image density data from the video controller
PCB.