Lexmark C500N, Service Manual, Page: 59 / 60

General information
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Laser drive control circuit
The laser drive control circuit (LDC) consists of a video signal input circuit, laser drive circuit, laser diode,
output sensing circuit, and output control circuit. See the illustration.
1. When the video signal is received, the laser drive control circuit switches the laser diode switch on and
radiates according to the video signal.
2. The radiated laser beam senses the photo detector (PD). The detected signal is returned to the output
control circuit.
3. The output control circuit controls the radiated output to a constant, by comparing the laser output
default with the feedback value transmitted from the output sensing circuit.
4. The laser beam, scanned by the scanner motor, is sensed by the beam detector (PD), and then outputs
the beam detecting timing (BDT) signal.