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 Power Supply; it tells the System
Controller PCB that the Arc Lamp is lit.
ODD_FIELD - Square wave signal from the Raster Timing Generator PCB, with
50% duty cycle that is low during odd fields of an Interlace signal. This signal is
high during noninterlaced signals. 
						

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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.
H_DRIVE - Square wave signal from Raster Timing Generator PCB, with a 50%
duty cycle synchronized to the selected horizontal sync.
V_DRIVE - Square wave from Raster Timing Generator PCB, with a negative
going pulse synchronized to selected vertical sync with a pulse width of about
four horizontal lines.
/FRONT_IR - command signals from the front infrared receiver.
/REAR_IR - command signals from the rear infrared receiver
H_F2V - DC voltage from the Raster Timing Generator PCB, proportional to the
horizontal frequency of the current source.
IIC CLK - IIC clock line, unidirectional clock line for control of synchronous data
transfer of data between PCBs.
IIC DATA - IIC data line, bi-directional serial data line for control of
synchronous data transfer between the System Controller PCB and the Raster
Timing Generator PCB.
+5.1 V Stdby - from the Low Voltage Power Supply when the AC Circuit Breaker
is turned on; it supplies power to the CPU, Interlock Switches, and IR Detectors
before the projector receives the POWER ON command.
+5.1 V  - from the Low Voltage Power Supply for all digital circuitry.
±15 V - from the Low Voltage Power Supply for all analog circuitry
GND - Ground
System Controller PCB - Outputs
/LV_ENA - signal to enable the Low Voltage Power Supply non-standby voltages
after the System Controller PCB receives the POWER ON command.
/FAN_ENA - signal to the Low Voltage Power Supply to turn on the +24 V stby
supply to turn on the cooling fans.
/LAMP_ENA - signal to enable the Arc Lamp Power Supply.
RGB_OVER - signal to Video Processor PCB for the On-screen Menu and /or
Internal Test Pattern for red, green, and blue.
OVERLAY - signal to the Video Processor PCB, to switch between internal and
external sources. 
						

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5-8 Model 250 Service Manual
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 signals to Convergence Deflection PCB for Red, Green,
or Blue Convergence in the x-axis (full-scale correction is about 1 Vpp).
CORR_SYNC - Square wave HCT level synchronous signal to the Convergence
Deflection PCB for the horizontal axis.
RGB_SHUT - Signal to operate the red, green, and blue shutters.
LENS_ZOOM - Signal to the zoom motor of the Projection Lens.
LENS_FOCUS - Signal to the focus motor of the Projector Lens.
System Controller PCB - Operation
Startup Functions
When AC Circuit Breaker is powered ON, the Low Voltage Power Supply sends
+5.1 V stdby voltage to the System Controller PCB. The +5.1 V Stdby powers the
CPU and IR Detector so the System Controller PCB can receive and respond to
the POWER ON command. The System Controller PCB sends a /FAN_ENA
signal back to the LVPS turning on the +24 V Stdby to turn the cooling fans on.
When the System Controller PCB receives a POWER ON command from either
the IR remote control or a PC, it sends the /LV_ENA signal to the Low Voltage
Power Supply. This turns on all the non-standby (±15 V, +5.1 V, +6.2 V, +24 V,
+80 V) voltages. After all the non-standby voltages power up, the LVPS sends the
/LV_OK signal back to the System Controller PCB to tell it that all the non-
standby voltages are present.
When the System Controller PCB receives a POWER ON command, it receives
the /LAMP_OK signal from the Arc Lamp Power Supply and sends the
/LAMP_ENA signal back to the Arc Lamp Power Supply to turn it on. The Arc
Lamp lights, and the Arc Lamp Power Supply sends a /LAMP_LIT signal back to
the System Controller PCB (see Figure 5-6).
The System Controller PCB also monitors the status of the High Voltage Power
Supply through the /HV_OK signal. 
						

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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 two RS-232 ports, labeled Terminal-in and Control-out, are functionally
almost identical. Both ports can be used to interface with computers, switchers, or
other remote controlling devices using a null modem cable. The difference is,
importing and exporting of configuration data can only be performed through the
Terminal-in. The dipswitch on the back of the System Controller PCB controls
the baud rate (see Figure 7-2).
The System Controller PCB enables the Video Processor PCB to select between
an internal and external source through the OVERLAY signal. The System 
						

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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 all the configuration data such as
Geometry, Convergence, Shading, ILA
® Bias and Sensitivity, and G2 settings etc.
in flash memory and allows that data to be exported to, or imported from a floppy
disk.
The System Controller PCB displays system status through a single three-color
LED visible on the back panel. A green light indicates normal operation, the
yellow indicates standby operation, and red indicates a fault or error condition.
The System Controller PCB has an External Service Mode Switch that enables the
operator to switch from the normal operating mode to a diagnostic mode. If there
is a new release of system software, it can be uploaded into the projector by
switching into the diagnostic mode. The procedure for this is in the Software and
Protocol section (see Chapter 8, Software and Protocol).
System Controller PCB - Remove and Replace
Tools Needed
#1 Pozi-drive Phillips-head screwdriver
#0 Pozi-drive Phillips-head screwdriver
Parts Needed
System Controller PCB - p/n 104678
To remove the System Controller PCB:
1. Power OFF the projector by IR Remote or PC, and allow the cooling fans
to run until they shut off automatically.
2. Turn the AC Circuit Breaker to the OFF position and unplug the AC
Power Cord.
3. Disconnect all the external source video cables and control cables.
4. Remove the rear cover.
5. Remove the Back Panel. Remove the nine Pozi-drive Phillips-head
retaining screws using the #1 Pozi-drive Phillips screwdriver.
6. Remove the Connector Bracket by removing the single Pozi-drive
Flathead Phillips-head screw using the #0 Pozi-drive Phillips screwdriver.
7. Pull the black Card Extractor handles back to disconnect the System
Controller PCB connector and pull the PCB out of the Electronics Module.
8. Reverse the procedure to install the System Controller PCB. 
						

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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, and
blue.
/SEL_VIC - input signal from the RGB VIC used to select the input source from
VIC #1.
RGB_OVER - from the System Controller PCB, the Menu overlays and internal
test patterns for red, green, and blue.
OVERLAY - from the System Controller PCB, switches between internal and
external sources.
CLAMP - Pulse signal from the Raster Timing Generator PCB, tells the Video
Processor PCB the timing and duration of the DC Restore.
BLANKING - Pulse signal from the Raster Timing Generator PCB, it tells the
Video Processor PCB the blanking interval during the scan.
RGB_THRESH - Threshold correction information for red, green, or blue from
the System Controller PCB. Real time data at 0-1 V.
RGB_SENS  - Sensitivity correction information for red, green or blue from the
System Controller PCB. Real time data at 0-1 V.
RGB_BEAM - sense signal proportional to the cathode current averaged over
several horizontal lines in the red, green, or blue CRT. The voltage level is +
mV/mA.
/VA_OK - signal from the Video Amplifier PCB telling the Video Processor PCB
the Video Amplifier PCB is receiving red, green, and blue deflections voltages
from the Horizontal Vertical Deflection PCB.
IIC_DATA - IIC data line. Bi-directional serial line for synchronous data transfer
between the System Controller PCB and Video Processor PCB.
IIC_CLK - IIC clock line. Unidirectional clock line for control of synchronous
data transfer over IIC bus. 
						

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

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Model 250 Service Manual 5-13
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 the proper level on the
Video Amplifier PCB. 
						

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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, the System Controller PCB polls
the VICs to determine what VICs are available. It then activates the VIC selected
in the Channel Menu (see section 4-6 in the User’s Guide). The selected VIC
sends a signal (/SEL_VIC) to the Video Processor PCB telling it which VIC is
active.
The Video Processor separates the sync pulses and passes them (H_SYNC and
V_SYNC) on to the Raster Timing Generator PCB. If the source sync type is
Sync-on-Green, the Video Processor strips the horizontal and vertical syncs from
the green input and sends that sync signal (G_SYNC) to the Raster Timing
Generator PCB.
The Video Processor PCB adjusts the image input information with contrast,
brightness, DC restore clamp, and blanking.  Contrast changes the peak to peak
amplitude of the External image while keeping the offset (black level) the same.
Brightness shifts the DC level of the External image up or down while keeping
the peak to peak amplitude the same. The DC restore circuit (or clamp pulse)
restores the DC offset (black level) after each horizontal line. Contrast and
Brightness commands come from the IIC data bus. The DC Restore and Blanking
signals come directly from the Raster Timing Generator PCB.
 The Video Processor PCB switches in the menu overlays and internal test
patterns. It performs gamma correction adjustments, and applies the shading
(sensitivity and threshold) adjustments. The menu overlay signals create the
displayed menus and test patterns. Menu overlays are generated on the System
Controller PCB. The gamma circuit corrects non-linearities, primarily due to the
ILA
®. Gamma correction consists of degrees of black and white boost. The
gamma tracking controls adjust the gain of the image information near the 50%
level.
Sensitivity and Threshold are shading adjustments that correct for non-uniformity
in the CRT and ILA
®. Sensitivity adjusts the gain (same as Contrast only local
instead of global) and threshold adjusts the DC offset (black level) (same as
Brightness, only local instead of global) to adjust the dark areas of the red, green,
or blue channel. The sensitivity and threshold commands come from the System
Controller PCB through the IIC bus and adjust both the internal and external
image information. Sensitivity and Threshold are applied to the image
information after the contrast, brightness and gamma correction. 
						

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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 Processor PCB protects the CRTs from excess beam currents to
prevent it from burning the phosphor. The Video Amplifier PCB sends a sample
of the beam current (RGB_BEAM) for each CRT back to the Video Processor
PCB. The Video Processor PCB compares this sample to a preset value. If the
sample beam current is higher than the preset value, the Video Processor PCB
reduces the contrast for the CRT with high beam current. If the CRT beam current
is still high, it then reduces the G
2 voltage. The maximum beam current is 250 µ A
per CRT.
The Video Processor PCB receives the G1_BIAS signal from the System
Controller PCB through the IIC bus and sends a voltage to the Video Amplifier
PCB to set the brightness level.
Figure 5-9  
Video Processor PCB LEDs.
Video Processor PCB  - Remove and Replace
Tools Needed
#1 Pozi-drive Phillips-head screwdriver
Parts Needed
Video Processor PCB  - p/n 105234
To remove the System Controller PCB:
1. Power off the projector by IR Remote or PC, and allow the cooling fans to
run until they shut off automatically.
2. Turn the AC Circuit Breaker to the OFF position and unplug the AC
Power Cord.
3. Disconnect all the external source video cables and control cables.
4. Remove the rear cover.
5. Remove the Back Panel by removing the nine Pozi-drive Phillips-head
retaining screws using the #1 Pozi-drive Phillips screwdriver.