Ricoh A-P4, Service Manual

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Each surface of the polygon mirror reflects two full main scan lines. The laser beams go to the F-theta mirror,
mirror, and BTL (barrel toroidal lens). Then these laser beams go to the drum through the toner shield glass.
The laser synchronization detector determines the main scan starting position.
• The front door and upper right door (transfer door) are equipped with safety switches that automat-
ically shut down the laser unit when either door is opened.
Auto Power Control (APC)
The LD driver on the LDDR drives the laser diode. Even if a constant electric current is applied to the laser
diode, the intensity of the output light changes with the temperature. The intensity of the output decreases
as the temperature increases.
In order to keep the output level constant, the LDDR monitors the electrical current passing through the
photodiode (PD). Then it increases or decreases the current to the laser diode as necessary, comparing it
with the reference level. This auto power control is done just after the machine is turned on and during
printing while the laser diode is active.
The reference levels are adjusted on the production line. Do not touch the variable resistors on the LDDR
in the field.
Dual-Beam Writing
This LD unit employs two laser diodes [A] (LD) and [B] (L2). Each face of the polygon mirror writes two
main scan lines, and twelve main scans are produced when the polygon mirror rotates once. This reduces
Laser Exposure
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