Bias Voltages And Laser Drive Timing - Epson ActionLaser 1600 Service Manual

Principles of Operation
If the SSCAN signal is not detected, the printer indicates a laser diode
malfunction. If the scanner mirror motor (M2) does not rotate, the printer also
indicates a laser diode malfunction.
Figure 2-26. Laser Diode Error Detection

Bias Voltages and Laser Drive Timing

Figure 2-27 is a diagram of the drum charge bias voltage, image transfer bias
voltage, doctor blade bias voltage, and the developing bias voltage control circuit.
These bias voltages are generated from the +24 VDC from the high voltage supply
board (PWB-F). If the printer detects a case open condition, the interlock switch
is set to OFF, which cuts the +24 VDC, which, in turn, cuts the bias voltages.
These bias voltages are controlled by the engine controller board (PWB-A). The
CH2:ON (HV-T) signal is the image transfer (roller) bias voltage control. While
this signal is LOW, the image transfer roller is charged to 3.2K VDC by the high
voltage supply circuit. And while this signal is HIGH, the image transfer roller is
charged to –0.8K VDC. The CH1:ON (HV-C/T. R) signal controls the drum charge.
While this signal is LOW, the PC drum is charged to --1.2K VDC.
The DB:CNT (HV-B.VR) signal is an analog signal for developing bias voltage
control. This signal controls the bias voltage level (–300V to --375K VDC) using
analog data. The image density is controlled by the developing bias voltage level.
Figure 2-27. High-Voltage Supply Block Diagram
2-22 EPSON ActionLaser 1600 Service Manual