JVC 330, 370 SC, 340 SC service manual Prism, Projection Lens, Arc Lamp Assembly

Chapter 2—Functional Description

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.

Model 330, 340SC and 370SC Service Manual 2-75