Hughes JVC Projector 250 Service Manual
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Chapter 4---Optical 4-8 Model 250 Service Manual Figure 4-5 Upper level view of Optical Path (top view). Optical Path - Inputs Arc Lamp high intensity white light Component RGB Image light from each of the ILA ® Optical Path - Outputs Component RGB polarized light to the ILA® Output image light to the Projection Lens Optical Path - Operation The light travels from the Arc Lamp into the Optical Path (see Figure 4-5). The light reflects off a cold mirror and passes through a light pipe. From the Light Pipe, the light passes through a Condensing Lens .The Condensing Lens also acts as a XY Positioner. The function of the XY Positioner is to aim the light beam down the optical path and center it on the face of the ILA ®. After being positioned by the Condensing Lens, the light then reflects off two more Cold Mirrors, losing more Infrared light. It passes through another Condensing Lens and into the Dichroic Beamsplitter Assembly.
Chapter 4---Optical Model 250 Service Manual 4-9 The Dichroic Beamsplitter Assembly separates the white light into its red, green, and blue components. Each component light beam goes into the Prism Assembly where it is polarized. Light can be viewed as having two electromagnetic components: a Horizontal- electric field and a Vertical-electric field. These fields are perpendicular to each other. When unpolarized light travels through a polarizing beamsplitter, one of these fields is reflected and one is transmitted or passes through the beamsplitter. Upon striking the Prepolarizer, the Vertical field is reflected and is wasted, the P- electric field is passed through the Prepolarizing Beamsplitter and continues on to the Main Polarizer. The Main Polarizing Beamsplitter (PBS) is rotated 90 ° from the Pre-Polarizing Beamsplitter so the Horizontal field that was transmitted through the Prepolarizer is reflected by the Main Polarizer. The reflected polarized light, either red, green or blue, leaves the PBS and goes directly into the ILA ® (see Figure 4-6 and Figure 4-7). Each color exits the Prism Assembly and enters an ILA ® where the Liquid Crystal in the ILA® rotates the polarized light. The image light striking the input side of the ILA® modulates the polarized light. The image on the input of the ILA® originates as a image signal and is transformed into an image by the CRT. The image from the CRT passes through the Relay Lens and is focused onto the input side of the ILA ®. The modulated image light leaves the output side of the ILA® and re-enters the Prism Assembly where all three colors combine in the 4P combining optic. The image light exits the Prism Assembly, passes through the Projection Lens, and is projected out on the screen (see Figure 4-7). WARNING!!! Wear safety goggles (rated X5) when working anywhere near the light path from the arc lamp or the projection lens. DO NOT open any of the Optical Support Assembly covers while the projector is ON. The bright light can cause severe eye damage.
Chapter 4---Optical 4-10 Model 250 Service Manual Figure 4-6 Optical Path
Chapter 4---Optical Model 250 Service Manual 4-11 Figure 4-7 Optical Path Optical Path - Service Adjustments Tools Needed 3-mm Hex wrench Parts Needed No serviceable parts The one adjustment that can be performed on the optical path is with the XY Positioner that moves the #1 Condensing Lens in the X- and Y-axis. The XY
Chapter 4---Optical 4-12 Model 250 Service Manual Positioner adjusts the light beam coming out of the Light Pipe so that it projects squarely onto the face of the ILA®. NOTE: Do not adjust the XY Positioner unless there is a dark edge visible on screen. If the XY Positioner is misaligned, there will be a dark edge on the left, right, top or bottom edge caused by the edge of the Light Pipe. Perform the Arc Lamp alignment before adjusting the XY Positioner unless the dark edge makes Arc Lamp alignment difficult or impossible. To adjust the XY Positioner: 1. Turn the projector ON and allow it to stabilize for at least 15 minutes. 2. Check the screen for dark edges on the top, bottom, left, or right. Check the screen with all three colors, using the Variable Flat Field (test pattern #4) or with ILA ® bias only. The dark edge will be obvious in either mode. 3. Remove the front cover. 4. There are four access holes; two with small notches on the top of the hole and two without notches (see Figure 4-8). Use the two access holes without notches. These holes are for full aperture ILA ®s. The upper access hole is for vertical adjustment; the lower one is for horizontal adjustment. 5. Insert a 3-mm (long shank) Hex-head wrench into either the horizontal or vertical access hole and adjust the XY Positioner until the dark edge moves off the screen. Figure 4-8 XY Positioner adjust holes.
Chapter 4---Optical Model 250 Service Manual 4-13 4.3 ILA® ILA® Main functions ! Modulates image light from the CRT onto the high intensity polarized light from the Arc Lamp ! Reflects high intensity light received from the Prism Assembly back into the Prism Assembly after modulating with image light ! Adjustable bias voltage and frequency (ILA® Sensitivity) ! Adjustable offstate with Super Contrast ILA®s ! Image light from CRT is blocked from output. Image is electrostatically coupled to output ILA ® Inputs Arc Lamp light - High intensity polarized Red, Green or Blue light from the Prism Assembly. Image light - Red, Green, or Blue image light from the CRTs. ILA ® Bias Voltage and Frequency - 10-13 Vac at 2 kHz ILA ® Outputs Image light - High intensity polarized image light output to the Prism Assembly and then to the Projection Lens and screen. Figure 4-9 ILA® structure
Chapter 4---Optical 4-14 Model 250 Service Manual ILA® Operation 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®. The image does not pass directly through the ILA® but is transferred by a change of impedance of the photoconductive layer to the Liquid Crystal Layer on the output side of the ILA ®. The light coming from the Arc Lamp enters the output side of 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 amount the liquid crystal rotates the polarized light depends on the ILA® Bias, ILA® Sensitivity (frequency), and CRT brightness (Sensitivity and Threshold). ILA ® Service Adjustments ILA® Bias and Sensitivity Adjustment The ILA® has adjustable bias and frequency (sensitivity). The ILA® bias and sensitivity are adjusted by software through the menu (see Model 250 User’s Guide, section 5.6 Setup Adjustments). The ILA ® bias is individually adjustable for each ILA®; the ILA® sensitivity (frequency) adjusts all the ILA®s together. Super Contrast ILA ® Compensator Adjustment The offstate level can be adjusted on Super Contrast ILA®s. The Compensator adjustment moves a lever on the top of each Super Contrast ILA® to a null 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 ® assembly or if the Compensator adjustment lever has been inadvertently moved. To set the Super Contrast ILA ® Compensator: 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 ® assembly. 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 ® connector to the green ILA®. 8. Repeat the above steps for the red ILA ® and blue ILA®. Block the light from the other two ILA®s each time, using the HIDE key. 9. Replace the rear cover.
Chapter 4---Optical Model 250 Service Manual 4-15 NOTE: Reset the ILA® bias after setting the Compensator and check G2 Sensitivity Offset, and Threshold Offset level (see Model 250 User’s Guide, section 5.8 Black Level G 2 and Sensitivity Offset). ILA ® Overlap This adjustment positions the ILA® assemblies in their sockets so that the image from each ILA® will overlap (be placed on top of) the other two ILA®s. Make this adjustment whenever replacing an ILA®. Tools Needed 4-mm hex-head wrench Flathead screwdriver Parts Needed No parts are needed To determine if this adjustment is necessary: 1. Power the projector ON and allow it to stabilize for at least 30 minutes. 2. Record the value of the ILA ® bias for red, green and blue. Return the ILA®s to these levels when this procedure is complete. 3. Under the System-Preferences menu, verify that the “Shutters on Hide” box is unchecked. 4. Use the HIDE key to hide red, green and blue. 5. Increase the ILA ® bias for all three colors to maximum. The image on the screen should be white with some colors at the edges. 6. Check the right, left, top, and bottom edges of the images on the screen. Using the green image as a reference, compare the edges of the red and blue image to the green image. 7. NOTE: If the green ILA ® has been replaced, reference green to the blue or red image.) 8. If there is a red or blue border on the left, right, top or bottom edge, the ILA ®s overlap and need adjustment. If both the red and blue overlap, the border will be yellow. In either case, proceed with the adjustment below. 9. If there is no overlap, reset the ILA ® biases to their previous levels from Step 1. To perform an ILA ® Overlap adjustment: 10. Continue with all three colors hidden. 11. Loosen the two wing nuts at the top of the ILA ® assembly (see Figure 4-10). 12. If the overlap is at the left or right, grasp the ILA ® assembly and slide it to the right or left so that the edges coincide with the edges of the other two ILA ® assemblies.
Chapter 4---Optical 4-16 Model 250 Service Manual CAUTION! To avoid damaging the connector, grasp the ILA® assembly itself, not the connector at the top. Figure 4-10 ILA® Assembly top view. The overlap screws shown are under the ILA®. They are visible only after the ILA® assembly is removed. 13. If the overlap is at the top or bottom, be sure the projector is level. Slide the spring clip (see Figure 4-10) at the top of the ILA ® assembly back. 14. Loosen the two hex nuts, using a 4-mm hex-head wrench. WARNING!!! Always wear an ANSI/ASTM 10,000 volt rated safety glove when working around CRTs due to the High Voltage present there. 15. Slide the ILA ®/Relay Lens/CRT Assembly back and remove the ILA® assembly (it will slide out with some resistance). 16. There are two adjustment screws at the bottom of the ILA ® assembly that move the ILA® up or down. Turn these screws in or out very slightly to allow the ILA® to seat lower or higher, as necessary. 17. Reinstall the ILA ® assembly, slide the ILA®/Relay Lens/CRT Assembly forward and replace the spring clip. 18. Repeat Step 4 as necessary.
Chapter 4---Optical Model 250 Service Manual 4-17 19. Retighten the two wing nuts and tighten the two hex nuts. 20. Reset the ILA ® biases to their previous levels from Step 2. ILA ® Back Focus Adjustment The ILA® Back Focus adjustment moves the ILA®/Relay Lens/CRT assemblies forward or backward as one unit to focus the ILA® output on the screen. When using a zoom lens this adjustment allows the zoom lens’ tracking to remain focused on the screen throughout the entire zoom range. Use the Focus Pattern (Test Pattern #6) to perform this adjustment one color at a time. The procedures below perform the ILA ® Back Focus for the Green lens. The first procedure is for a zoom lens. The second procedure is for a fixed lens. For best results, perform ILA ® Back Focus procedure with two people: One person to stand in front of the screen to observe Spacer Balls and the other to move the ILA ®/Relay Lens/CRT assemblies back and forth. This is a factory-set adjustment, but may need some touch-up in the field. Tools Needed 4-mm Hex wrench 2.5-mm Hex wrench Parts Needed No parts are needed To adjust the ILA ® Back Focus for a Zoom Lens: 1. Power the projector ON and allow to stabilize for at least 15 minutes 2. Remove the Rear Cover and tilt up the Electronic Module. 3. Hide Red and Blue. View Green. 4. Select the Focus Pattern (Test Pattern #6). 5. Select Projection Lens from the menu. 6. Use the up/down arrow keys to zoom the Projection Lens to full telephoto position (smallest image). 7. Use left and right arrows to focus the projection lens to get sharply focused spacer balls. NOTE: Spacer balls separate the layers inside the ILA ® Assembly. They are tiny, random, irregularly shaped spots that are visible throughout the image. Stand directly in front of the screen and look in the lighter areas of the image to see the Spacer balls. From throw distances shorter than 4 meters, spacer balls are difficult to see. 8. Zoom the lens to a wide-angle position (largest image). 9. Loosen the wing nut on the Green Relay Lens (or whichever lens is being focused).