Canon LBP 2460 - B/W Laser Printer Service Manual page 65

1. Outline
In response to the instruction from the microprocessor (CPU) on the DC controller PCB, the
high-voltage power supply applies a voltage to the primary charging roller, developing cylinder,
transfer charging roller, static charge eliminator, and upper fixing roller. It applies a voltage of
DC voltage and AC voltage to the primary charging roller and developing cylinder, applies a
positive or negative DC voltage to the transfer charging roller, and a negative DC voltage to the
static charge eliminator and the upper fixing roller.
2. Principle of operation
a. Primary charging roller voltage generation
When the /PRNT signal sent from the video controller becomes "L", initial rotation starts, the
DC controller outputs the primary bias FREQUENCY OUTPUT signal (/HV1FRQ). The circuit
then applies the primary AC bias to the primary charging roller. After the specified period of
time has elapsed the PRIMARY DC BIAS DRIVE signal (/HV1DCD) goes "L" and the voltage
superimposing primary AC bias onto primary DC bias is applied to the primary charging roller.
The primary DC bias changes with the developing DC bias according to the IMAGE
DENSITY ADJUSTMENT signal (DENADJ) sent from the DC controller.
b. Developing bias generation
When the DEVELOPING DC BIAS DRIVE signal (/DBDCD) from the DC controller becomes
"L", a developing DC bias is applied to the developing cylinder.
When the VERTICAL SYNC signal (/VSYNC) is sent from the video controller, the DC
controller outputs the DEVELOPING AC BIAS DRIVE signal (/DBACD) and DEVELOPING
BIAS FREQUENCY OUTPUT signal (/DBFRQ). This circuit then applies the voltage
superimposing developing DC bias and developing AC bias to the developing cylinder.
The developing DC bias changes according to the IMAGE DENSITY ADJUSTMENT signal
(DENADJ), making the image density adjustable.
c. Transfer charging roller voltage generation
The negative, between-page, and print bias are applied to the transfer charging roller according to
the print sequence.
The negative bias voltage is applied to the transfer charging roller at an appropriate timing to
move the toner attached to the transfer charging roller onto the photosensitive drum to clean the
roller.
For the between-page bias, a positive low voltage is applied to the transfer charging roller at
an appropriate timing so that the toner remaining on the photosensitive drum is not attracted to
the transfer charging roller.
For print bias, a positive voltage is applied to the transfer charging roller in order to transfer
the toner on the photosensitive drum surface to the paper.
When the /PRNT signal sent from the video controller becomes "L", initial rotation starts and
a negative bias is applied to the roller for a certain time to clean the transfer charging roller.
Between-page bias is then applied, and a print bias is applied to the transfer charging roller after
the prescribed time has elapsed since the /VSYNC signal going "L".
A print bias is applied during the print sequence to transfer the toner onto the paper. A
between-page bias is applied between pages.
After the completion of printing, a between-page bias and a negative bias are applied again to
clean the transfer charging roller.
d. Generation of print voltage to the discharger
2 voltage loads, high and low output bias are applied to the discharger according to the various
print sequences.
The discharger bias drive signal (/DCHGBD) output from the DC Controller is "L", and when
the discharger bias switch signal (/DCHGUP) turns "H" the low output bias changes to "L" and
CHAPTER 2
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