Hughes JVC 220, Service Manual

Page: 77 / 140

Chapter 3 Service Adjustments
4. From the System menu, select Maintenance, then select #3,
ILA® Bias. Record the ILA® Bias present value (the Green
bias will be readable). This bias value will be returned to when
this procedure is complete. Only the Green value needs to be
recorded. Red and Blue return to their original values when
Green is reset.
5. Use the right arrow key to increase the ILA
®
Bias so the Flat
Field turns white. If the screen begins to turn from white to a
yellow-tinge, use the left arrow and adjust the bias back until an
all white flat field is observed. The flat field screen must be
white to properly perform the arc lamp focus.
6. Defocus the Arc Lamp by turning the Z-axis Focus Adjust
Screw ( see Figure 4-4 ) until a bright, circular area ( Figure 3-3 )
is achieved. This is the Arc Lamp’s “hot spot.” The sides, top,
and bottom areas will taper off in brightness. When performing
defocus, do not attempt to narrow the circle too much. Try to
obtain a uniform circular area.
NOTE: The Model 220 uses an integrated lamp/reflector system.
Normally no adjustment is required, except for Z-axis focus, when
replacing the arc lamp. It is not possible to predict how much
variation there will be from lamp to lamp. The adjustment
procedure below for the first condensing lens should be performed
only when the location of the "hot spot" on the screen is
extremely
offset from the center of the screen. If the "hot spot" is not
extremely off center, skip steps A through G. CAUTION! This
procedure should not be undertaken unless absolutely necessary .
A. Turn projector power off at the remote.
B. Wait for the Arc Lamp cooling fans to stop and turn the
circuit breaker on the rear panel off.
WARNING!!!
Some components under the Optical Shield,
especially the First Condensing Lens and nearby components,
are still hot! Before removing the Optical Shield (Step C below)
wait at least 10 minutes for these components to cool down.
C. Remove the Optical Shield (see Figure 4-1 ) by removing the
four screws holding it. Place the Optical Shield in the
manner shown in Figure 3-2 so that it blocks the light from
the lamp but still allows enough room to adjust the
condensing lens Retainer Ring.
D. Using a 7mm open end wrench, s lightly loosen (about ½ turn
or so) the 3 nuts that hold the First Condensing Lens
(
Figure 3-1 ). Do not loosen these screws too much or it
becomes more difficult to perform small adjustments.
3-2 Model 220 Service Manual