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Chapter 2—Functional Description
Model 330, 340SC and 370SC Service Manual 2-75
Prism
The prism receives the high intensity light from the xenon arc lamp and polarizes
the light horizontally. The prism reflects virtually all of this light toward the ILA
®
assembly. This light is then phase modulated into a vertical plane by the input side
of the ILA
®
assembly and then reflected back toward the same prism. Since the
prism reflects only horizontal light and passes vertical light, this high intensity,
vertically polarized image goes straight through the prism and into the projection
lens.
Projection Lens
The projection lens picks up the high intensity image from the prism and transmits
it to the projector screen. The projection lenses are individually mounted so they
can be focused and aligned separately. The green lens is fixed horizontally and the
red and blue lenses allow horizontal movement to align them with the green lens.
Various focal lengths, (focal length = throw distance/screen width), are available
for different sized rooms and screens.
Arc Lamp Assembly
The high intensity light from the Xenon Arc Lamp produces a “full screen” output
of between 3,000 and 6,800 lumens, depending on the model of projector. The
output from the arc lamp, along with the output from the ILA
®
Assemblies,
produces the images on the screen.
NOTE:
To protect equipment and personnel against explosion hazard, the arc
lamp is covered with a safety glass plate and is mounted in a protective metal
housing. This housing provides protection and ensures accurate alignment of the
arc lamp optical axis with the projector housing by means of machined surfaces
and precision alignment pins.
The Arc Lamp itself, a gas-filled device, maintains a relatively constant voltage.
It, therefore becomes the voltage controlled device and the SPS Arc Lamp supply
controls the current to the lamp. The constant voltage maintained by the lamp and
the constant current provided by the SPS result in a constant power supplied to the
Arc Lamp.
The arc lamp and reflector housing is never disassembled in the field. The arc
lamp is replaced by exchanging the complete assembly.
The Arc Lamp Assembly also includes the Ignitor and its circuitry. The Ignitor
circuit provides a momentary high voltage that excites the xenon gas inside the
Arc Lamp. After the arc lamp is struck and turns on, it is maintained by a high-
current, low-voltage power supply.