Canon LBP-1760, Service Manual

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The primary DC bias changes with the developing DC bias according to the IMAGE DENSITY
ADJUSTMENT signal sent from the CPU.
b. Developing bias generation
When the DEVELOPING DC BIAS FREQUENCY OUTPUT signal is output from the CPU, the cir-
cuit applies the developing DC bias to the developing cylinder.
Then, the CPU outputs the DEVELOPING AC BIAS FREQUENCY OUTPUT signal at the tim-
ing of image formation, and applies developing AC bias to the developing cylinder. Following
that, the circuit applies superimposed voltage of developing AC bias onto developing DC bias to
the developing cylinder.
The developing DC bias changes according to the IMAGE DENSITY ADJUSTMENT signal out-
put from the CPU, and adjusts the image density.
c. Transfer charging roller voltage generation
The negative, between-page, or print bias is applied to the transfer charging roller according to
the print sequence.
The negative bias (voltage negative) is applied to the transfer charging roller at an appropri-
ate timing to move the toner attached to the transfer charging roller onto the photosensitive
drum to clean the roller.
The between-page bias (positive low voltage) is applied to the transfer charging roller at an
appropriate timing so that the residual toner on the photosensitive drum is not attracted to the
transfer charging roller.
The print bias (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
negative bias is applied to the roller for a certain period of time to clean the transfer charging
roller. Between-page bias is then applied, and print bias is applied to the transfer charging roller
after the prescribed time has elapsed after the CPU outputs the /TOP signal.
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. Toner level detection/cartridge detection
The EP-52 cartridge has a toner sensor.
The circuit compares the output value of the developing AC bias and the output value (ANT)
from the antenna inside the cartridge, and outputs the TONER DETECTION signal.
The CPU detects the toner level and whether the cartridge is installed or not when the devel-
oping AC bias is applied to the developing cylinder. The toner level is always detected when the
developing AC bias is applied, and the cartridge is detected only when the developing AC bias is
applied during the initial rotation.
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CHAPTER 2