EN Chapter 5 Theory of operation 101
Laser/scanner drive
The HP LaserJet 4100 series printer has two diodes in the laser/scanner assembly. The printer uses
a twin-beam method to scan two lines simultaneously. Based on information received from the
formatter, the engine controller board sends signals to the laser scanner assembly to modulate the
laser diodes on and off and to drive the laser scanner motor. See “Image formation system” on page
108 for more information.
Paper-motion monitoring and control
The engine controller board controls paper motion by continuously monitoring the various paper
sensors and coordinating paper movement with the other print processes. For more information, see
“Paper feed system” on page 117.
Solenoids, sensors, clutches, and switches
The engine controller board monitors the various sensors and switches in the printer and controls the
solenoids and clutches for paper movement. See "Engine controller board inputs and outputs" on
pages 96 through 100.
Engine test print
The engine controller board has a built-in engine test pattern that can be printed without using the
data from the formatter. See “Engine test” on page 190 in chapter 7.
Motors
See “Timing diagram” on page 131 for specific timing details for the printer motors.
This printer and optional input trays are driven by the main motor, which is controlled by commands
from the CPU.
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