User manual

95.08.23.11.30
Color LaserWriter 12/600 PS Basics & Theory 1–87
At each of the five intervals specified previously, the DC controller
prints a series of patches directly onto the transfer drum. The light
emitted by the PS14 LED is reflected off these patches and back into
the photodiode of PS14.
The reflective characteristics of colored toner and black toner differ.
Therefore, this sensing circuit uses the density sense mode select signal
(
/DSEL) to switch between the colored toner density sensing mode and
the black toner density sensing mode.
When the density sense enable signal (
/DENB) goes “L,” the LED emits
light with the intensity provided by the LED power control signal (
/D0-
7). The photodiode senses the light, which is reflected by the density
sensing pattern on the transfer drum. The density sensing board outputs
the density to the DC controller as the toner sensor signal (
DSNS).
Note: If the DC controller determines that sensor PS14 is blocked, it
will still allow printer operation to continue but will default to factory
density settings.
DC Controller Board
IC101
/DENB
DSNS
/DSEL
Receiver
(PS14)
/D0 to 7
Emitter
Density Sensing Board
Calibration Density Sensor
CPU
Density
Sensing
Circuit