Hughes JVC Projector 250 Sc Service Manual

Chapter 5---Electronics
5-6 Model 250 Service Manual
Figure 5-5  
System Controller PCB I/O Diagram for other PCBs.
System Controller PCB - Inputs
/LV_OK - signal from the Low Voltage Power Supply; it tells the System
Controller PCB that all the non-standby supply voltages are working.
/HV_OK - signal from the High Voltage Power Supply; it tells the System
Controller PCB that all the high voltage supplies are working.
/LAMP_OK - signal from the Arc Lamp Power Supply.
/LAMP_LIT - signal from the Arc Lamp...

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Model 250 Service Manual 5-7
280_CLK - Square wave signal from the Raster Timing Generator PCB, with
50% duty cycle, synchronized to the horizontal sync at 280 times the frequency of
the horizontal sync. This signal is used by the System Controller PCB to properly
output shading and convergence data.
SOURCE_VALID - Signal from Raster Timing Generator PCB indicates a new
source (or valid source). A high indicates a valid stable signal and a low indicates
a change in input signal....

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RGB_THRES - red, green, or blue Threshold correction information to the Video
Processor PCB.
RGB_SENS - red, green, or blue Sensitivity correction information to the Video
Processor PCB.
ISYNC - 5 MHz clock to the Raster Timing Generator PCB, used to generate the
internal sync signals
Y_RGB_CONV - control signals to Convergence Deflection PCB for Red, Green,
or Blue Convergence in the y-axis (full-scale correction is about 1 Vpp).
X_RGB_CONV - control...

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Model 250 Service Manual 5-9
Figure 5-6  
Power On timing sequence.
Normal Operation Functions
During normal projector operation, the System Controller PCB receives
commands through the remote control, tethered remote control, or a PC.
Commands issued from the IR remote controls are received through IR Detectors
located on the front and rear of the projector. Commands issued from a PC,
Laptop, or Tethered Remote Control are received through the RS-232 serial
interface ports.
The...

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5-10 Model 250 Service Manual
Controller PCB also enables the selected VICs through the IIC bus based on the
VIC selected on the Channel Menu.
The System Controller PCB generates the on-screen menus and test pattern
overlays and sends them to the Video Processor PCB. It sends the X and Y
Convergence correction data to the Convergence Deflection PCB. It sends
Threshold and Sensitivity shading data to the Video Processor PCB for the all
three colors. The System Controller PCB stores...

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Model 250 Service Manual 5-11
5.4  Video Processor PCB
Video Processor PCB - Main Functions
!
 Video signal input and multiplexing
!
 Sync signal stripping
!
 Overlay signal multiplexing
!
 Brightness, Contrast, DC Restore and Blanking
!
 Video signal gamma correction
!
 Sensitivity and Threshold signal input and control
!
 Automatic Contrast, G2, and internal image limiting
Video Processor PCB  - Inputs
RGBHV VIC 1,2, & 3 - External image signals from the VICs for red, green,...

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Figure 5-7  
Video Processor PCB I/O diagram for VICs and Power Supplies. 

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Figure 5-8  
Video Processor PCB I/O diagram for PCBs.
Video Processor PCB  - Outputs
RGB_VID - red, green, or blue video signal to Video Amplifier PCB, typically 0-
1 V.
H&V_SYNC - horizontal sync pulse goes to the Raster Timing Generator PCB.
GRN_SYNC - sync-on-green sync pulse goes to the Raster Timing Generator
PCB.
RESTORE - DC Restore control signal to the Video Amplifier PCB. This signal
controls the DC level of the image signal, clamping it to...

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RGB_G2 - red, green, or blue G2 voltage adjust control signal to the Video
Amplifier PCB.
G
1_BIAS - G1 adjust control voltage (global adjustment) to the Video Amplifier
PCB.
IIC_INT - IIC interrupt output to System Controller PCB.
Video Processor PCB  - Operation
The Video Processor PCB accepts image and synchronizing inputs in either
composite or separate RGBHV component format from the selected VIC. When
the projector receives the power ON command,...

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The G2 voltage accelerates the electrons that are emitted from the cathode of the
CRT. The CRT filament emits the electrons and G
1 voltage regulates the amount
of electrons that are emitted from the cathode. The G
2 voltage is adjusted through
the menu (Black Level). The Video Processor PCB receives the G
2 control data
for each color through the IIC bus and sends an analog voltage to the Video
Amplifier PCB to control the G2 voltage.
The Video...