Hughes JVC 100, Service Manual

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Chapter 2---System Description
2-6 Model 100 Service Manual
The polarized light from each of the PBS’s enters the ILA
®
and is rotated and
modulated with the image signal. The amount the polarized light is rotated is
controlled by the ILA
®
bias and the amount of CRT light hitting the input side of
the ILA
®
, and translates directly to the brightness of the image on the screen.
The image light from each of the ILA
®
s is then sent back through the Main
Polarizer portion of the PBS. The polarized blue image light continues on to a
Turning Prism where it is reflected into the 2P Combining Prism. The red and
green light come from their respective PBSs and are combined in the1P
Combining Prism. From the 1P Combining Prism, the red and green image light
go into the 2P Combining Prism to combine with the blue image light, where the
RGB image light goes through the Front Projection Lens and out onto the screen.
This completes the Illumination Path.
CAUTION!
The alignment of system optical components is
critical. Replacement of individual mirrors or prisms requires removing the
projector cover and must be performed only by Hughes-JVC Certified
technicians. Consult the factory before removing or aligning any mirrors or
prisms.
CRT \ ILA
®
Module
The three CRT/ILA
®
assemblies are located in the main body of the projector
above the Dichroic Filters and in front of the Electronics Module card cage. The
red CRT is separated and perpendicular to the green and blue CRT. Two exhaust
fans at the rear help cool the green and blue CRT assemblies. Each CRT is sent a
red, green, or blue image signal, but they do not emit a red, green, or blue color, as
in traditional CRT projectors. The CRTs are not used as a primary light source.
The light output to the screen is the function of the Arc Lamp, ILA
®
bias, and
CRT output. The purpose of the CRT is to generate an image and to control the
amount of modulation the ILA
®
assemblies introduce on the light coming from
the Arc Lamp. The Red, Green, and Blue image signals are routed to the CRTs
from the Video Amplifier Board through the CRT socket connectors.
The CRT
image passes through a thin fiber-optic coating on the CRT face and another fiber-
optic on the back surface of the ILA
®.
There is a thin layer of optical fluid
between the two fiber optic coatings. The input and output sides of the ILA
®
assembly are isolated from each other electrically and optically but are coupled
electrostatically.
At the same time the image is received at the input side of the ILA
®
, the output
side of the ILA
®
is receiving high intensity polarized light from the arc lamp
through the PBS. This high intensity polarized light is modulated by the image
from the CRT and the light polarization is rotated (90
°
at 100% CRT output) by
the liquid crystal on the output side of the ILA
®
. The light is then reflected back