Brother HL-2700CN Service Manual page 88

(2) Laser Drive Control Circuit
Laser Drive Control Circuit (LDC) consists of the video signal input circuit, laser
drive circuit, laser diode, output sensing circuit and output control circuit, as shown
in Fig.4-33.
<Operation>
(1) When the video signal is inputted, the laser drive control circuit has the laser
diode switched on and radiated according to the video signal.
(2) Radiated laser beam is sensed by the photo detector (PD), and the detecting
signal is fed back to the output control circuit.
(3) Output control circuit controls the radiation output to be constant, by comparing
the laser output default with the feed-back value transmitted from the output
sensing circuit.
(4) Laser beam scanned by the scanner motor is sensed by the beam detector
(PD), and then, the beam detecting timing (BDT) signal will be outputted.
PRINT Signal
VIDEO Signal
MCTL PWB 2
Frequency Control
Circuit
Beam Scanning
Control Circuit
Synchronizie
Control Circuit
BDT
LCD PCB
Fig.4-33
IV-35
OPC Belt
F-θLens
Scanner Motor
Laser