JVC 250 Service Manual page 47

Chapter 4---Optical
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ILA Operation
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The ILA plays a critical part in bringing the image to the screen. The ILA
receives the image light when the CRT projects the image through the Relay Lens
and focuses it onto the photoconductive layer on the input side of the ILA
image does not pass directly through the ILA
impedance of the photoconductive layer to the Liquid Crystal Layer on the output
side of the ILA
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the ILA and passes through the Liquid Crystal layer. Here the polarized light is
rotated according to the orientation of the liquid crystal molecules. It then reflects
off the mirror and passes back through the liquid crystal layer. The polarized light
it is rotated again and then exits the ILA
the polarized light depends on the ILA
CRT brightness (Sensitivity and Threshold).
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ILA Service Adjustments
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ILA Bias and Sensitivity Adjustment
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The ILA has adjustable bias and frequency (sensitivity). The ILA
sensitivity are adjusted by software through the menu (see Model 250 User's
Guide, section 5.6 Setup Adjustments). The ILA
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for each ILA
Super Contrast ILA
The offstate level can be adjusted on Super Contrast ILA
adjustment moves a lever on the top of each Super Contrast ILA
position. The null position is where the offstate level is as dark as possible. The
Compensator is set at the factory and should not need adjustment. Perform this
procedure when replacing an ILA
lever has been inadvertently moved.
To set the Super Contrast ILA
1. Power the projector ON and allow it to stabilize for at least 30 minutes.
2. Remove the rear cover and tilt the Electronics Module up.
3. Under the System-Preferences menu, verify that the "Shutters on Hide"
box is checked.
4. Use the HIDE key to hide red and blue.
5. Disconnect the connector from the top of the green ILA
6. Move the Compensator lever (this lever is just in front of the ILA
connector) to the right and left until the darkest level appears on the
screen.
7. Reconnect the ILA
8. Repeat the above steps for the red ILA
from the other two ILA
9. Replace the rear cover.
4-14
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. The light coming from the Arc Lamp enters the output side of
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; the ILA sensitivity (frequency) adjusts all the ILA
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Compensator Adjustment
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Compensator:
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connector to the green ILA
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s each time, using the HIDE key.
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but is transferred by a change of
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. The amount the liquid crystal rotates
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Bias, ILA Sensitivity (frequency), and
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bias is individually adjustable
assembly or if the Compensator adjustment
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.
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and blue ILA
Model 250 Service Manual
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. The
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bias and
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s together.
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s. The Compensator
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to a null
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assembly.
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. Block the light