Brother International HL-3400CN Service Manual - Page 90

HL-3400CN SERVICE MANUAL (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.434. (1) When the video signal is received, the laser drive control circuit switches the laser diode according to the video signal data. (2) The radiated laser beam is sensed by the photo detector (PD) and the signal is fed back to the output control circuit. (3) The output control circuit controls the laser output to make the level constant by comparing the laser output with the feed-back value transmitted from the output sensing circuit. (4) The scanning laser beam is sensed by the beam detector (PD), then the beam detecting timing (BDT) signal is output. ! PRINT Signal VIDEO Signal -:-0. ! MCTL PWB ! Frequency Control Circuit 4 OPC Beft N. .., .... \\ .., ....' oo- PD Scanner Lens i i cb 4 .4 Beam Scanning Control Circuit Synchronizie Control Circuit ,•• I* )).. LDC PCB BDT 4 Laser Scanner Motor Fig. 4-34 4-39