Hughes JVC Projector 250 Sc Service Manual

Chapter 5---Electronics
5-46 Model 250 Service Manual
Figure 5-27  
Video Amplifier PCB I/O Diagram for the Video Processor PCB and
CRTs.
Video Amplifier PCB - Outputs
RGB_BEAM - Cathode beam current sense lines (about 1 V per 100 µ A).
RGB_CATHODE - image output signal to CRTs (about 40 Vpp with peak
voltage of 70 V).
RGB_G
1 - G1 voltage to CRTs (Blanking pulse to CRT).
RGB_G
2 - G2 voltage for CRTs (about 600-800 V).
RGB_HEAT (pos.) - positive side of the CRT heater voltage (about 6.2 V). 

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RGB_HEAT (neg.) - negative side of CRT heater voltage (ground level).
ARC_GND - CRT ground back to High Voltage Power Supply (CRT Protection
against arcing).
/VA_OK - CRT Protection signal to the High Voltage Power Supply (low = good,
high = bad). This signal is becomes /HV_ENA at the High Voltage Power Supply.
Video Amplifier PCB - Operation
Image Amplifier
The main function of the Video Amplifier PCB is to amplify each of the image
signals going to...

Chapter 5---Electronics
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The Video Amplifier PCB detects all the necessary supply voltages (+80 V, +15
V, and the +6.2 V) for the CRT and includes that as part of the /VA_OK signal. If
any of the supply voltages is not present, /VA_OK goes high, again shutting down
the G1 and G2 regulators. The /VA_OK goes out to the High Voltage Power
Supply as the /HV_ENA. If the /VA_OK goes high, the /HV_ENA goes high and
shuts down the high voltage amplifier section of the High Voltage...

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5. Remove the green CRT by loosening the green CRT Holder Ring (see
Figure 5-29). Perform this step with the CRT Socket Connector still
connected to the Green CRT and the ground wire still connected from the
CRT/Yoke Assembly to the CRT Socket Connector. The Green CRT
Socket Connector is close to the rear of the projector. It is easier to
disconnect it from the CRT after the CRT/Yoke Assembly is loose and
moved away from the rear of the projector (see...

Chapter 5---Electronics
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12. Disconnect the three Focus cables that run from the CRT Socket
Connectors to the Focus connectors on the HVPS.
NOTE:
 Observe that each of the three Focus cables (large, red wires that
run from each CRT Socket Connector to the Focus connectors on the
HVPS) is joined near the CRT by a coupler plug and jack. Disconnect
(and label) the focus cables at these couplers.
13. Loosen the six Pozi-drive Phillips-head screws that secure the Video
Amplifier...

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5.10  CRT/Yoke Assemblies
CRT/Yoke Assemblies - Main Function
!
 CRTs converts image signal to image light
!
 Yokes provide horizontal and vertical deflection for CRTs
!
 Yokes provide x-axis and y-axis convergence correction for CRTs
CRT/Yoke Assemblies - Inputs
To Yokes
H_RGB_YOKE (pos.) - top of red, green, and blue horizontal yokes.
V_RGB_YOKE (pos.)  - top of red, green, and blue vertical yokes.
RGB_LOCK (pos.) - interlock for red, green, and...

Chapter 5---Electronics
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Image - image light that passes through Relay Lens and focuses on photosensitive
layer on input side of ILA®.
CRT/Yoke Assemblies - Operation
The CRTs receive image signals that come from the VICs to the Video Processor
PCB, to the Video Amplifier PCB. The image information drives an electron gun
inside the CRT. The Cathode of the CRT is a small, metal oxide disk that covers
the filament heater. The filament heater heats the Cathode causing it to...

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CRT Mechanical Focus
The CRT Mechanical focus is factory-set and normally will not require additional
adjustment unless a CRT has been replaced. After replacing a CRT, reset the
mechanical focus. After completing the CRT installation and mechanical focus,
check the other CRTs for convergence and shading.
Tools Needed
1.5-mm Hex-head wrench
#0 Pozi-drive Phillips-head screwdriver
To adjust the CRT Mechanical Focus:
1. Remove the rear cover.
2. Pull the...

Chapter 5---Electronics
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Figure 5-29  
CRT Mechanical Focus adjustments.
CRT Rotation
The CRT tilt adjustment aligns the CRT level with the screen. This is a factory-set
adjustment and should not need adjusting unless the CRT or yoke is moved.
Tools Needed
1.5-mm Hex-head wrench
#0 Pozi-drive Phillips-head screwdriver
3-mm Hex-head wrench
To perform the CRT Rotation adjustment:
1. Remove the rear cover.
2. Power the projector ON and allow it to stabilize for at least 15...

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5. View the color for the CRT that requires rotation. Hide the other two
colors.
6. In the Geometry menu, set “Reg Enable” to off by unchecking the box.
Unchecking the Reg Enable box temporarily disables any convergence
corrections that have been performed with a different CRT/Yoke assembly
and sets these values to the default levels so that CRT Rotation can be
accomplished correctly.
7. In the Geometry menu, access Bow, Skew, Pincushion, and...