Hughes Model 230 Projector Service Manual

							Chapter 2---System Description
Model 230 Service Manual2-19
R
G
B
/H
/SELECT Comp
Y in
C in
IIC_CLK
IIC_DATA
+5.1V
+15VB2
B4
B6
B8
B12 B13
A13
B16
B15
Pin callouts are to P12, P14, 
or P18, depending on which
VIC slot is being used.
/V
B10
Figure 2-9.   Quad Standard Decoder I/O Diagram.
LED Indication
There are two LEDs on this VIC. The LED on the right side of the board glows
when Composite Video is selected and the LED on the left glows when S-Video
is selected. Only one LED can light at one time.
IIC Interface
The Quad Standard Decoder VIC is controlled by the serial bus interface. The
IIC bus comes from the System Controller Board through the Backplane Board.
All required adjustments for this board are provided via the IIC serial bus
interface. The information transferred over the IIC bus is indicated below (I =
input to YPbPr_VIC, and O = output of YPbPr_VIC). The selection of this VIC is
accomplished through the IIC control bus which provides the /SEL_VIC signal.
Table 2-6.  Quad Standard Decoder VIC IIC Interface
I/O INFORMATION DESCRIPTION
I SOURCE Selects input source (Composite Video or S-
Video)
I STANDARD Selects signal standard
(AUTO/NTSC/PAL/SECAM/4.43NTSC) 
						

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2-20Model 230 Service Manual
I TINT Data for adjustment of Hue
I COLOR Data for adjustment of color
I SHARP Data for adjustment of Sharpness
I VTR Selection of VTR mode
O VNR Selection of Video Noise Reduction mode
Quad Standard Decoder VIC I/O
This section provides a description of the inputs to and outputs from the Quad
Standard Decoder VIC. The I/O descriptions are arranged by the
source/destination of the signal. The format used is such that the assembly
communicated with is used as the primary heading of each group of signals.
Those signals are further subdivided into inputs and outputs. Input refers to an
Input to the VIC, output refers to an output from the VIC.
Table 2-7.   Quad Standard Decoder VIC Signals
PROJECTOR INPUTS
INPUT DESCRIPTION
Composite V Video input signals-about 0.7 to 1 VPP
S-Video Video input signal-about 0.7 to 1 VPP for Luminance and about .3-.6
VPP for Chrominance (Burst)
VIDEO PROCESSOR BOARD
OUTPUT DESCRIPTION
/SELECT Selection indicator for VIC. Low indicates the Quad VIC is selected.
RED
GRN
BLUVideo signals. about 0.7 to 1 VPP
H, V Horizontal/vertical sync signals, about 1-1.25 VPP
SYSTEM CONTROLLER BOARD
INPUTS DESCRIPTION
IIC_CLK IIC clock line. Unidirectional clock line for control of synchronous
data transfer over the IIC bus interface.
IIC_DATA IIC data line. Bidirectional serial line for synchronous data transfer
between System Control Board and the VIC. 
						

							Chapter 2---System Description
Model 230 Service Manual2-21
LOW VOLTAGE POWER SUPPLY
INPUTS DESCRIPTION
+5.1 V +5.1 V supply for use by The Quad Decoder VIC.
+15 V + 15 V supply for use by the Quad Decoder VIC.
Interlocks and protection
None
2.3.4  Video Processor PCB
The Video Processor Board (VPB) is the bottom-most card (see Figure 5-1) in
the card cage. It is connected directly to the Backplane board through 2
connectors. When an external signal is being received, the VPB provides
Horizontal Sync, Vertical Sync, and Green Sync signals to the Raster Timing
Generator (RTG) board. It also provides three primary color signals, and G2, G1
bias and DC RESTORE control signals to the Video Amplifier Board (VAB).
The following functions are provided by the VPB:
•  Video signal input and multiplexing
•  Sync signal stripping
•  Overlay signal multiplexing
•  Brightness and Contrast control, and DC RESTORE
•  Video signal gamma correction
•  Sensitivity and Threshold signal input and control
•  Automatic limiting for Contrast, G2, and internal video
The Video Processor I/O diagram and the list of inputs and outputs provide
information to allow the technician to perform module-level troubleshooting. 
						

							Chapter 2---System Description
2-22Model 230 Service Manual
B31   RED_VIC#1
B29   RED_VIC#2
B27   RED_VIC#3
B23   GRN_VIC#2
B21   GRN_VIC#3
B19   BLU_VIC#1 B25   GRN_VIC#1
B24  RED_THRESH
B23  GRN_THRESH
B22  BLU_THRESH B25  BLU_SENSB17   BLU_VIC#2
B15   BLU_VIC#3
B13   H_VIC#1
B9     H_VIC#3
B7     V_VIC#1
B5     V_VIC#2B11   H_VIC#2
B3     V_VIC#3
GRN_G2    A20
BLU_G2     A21 
G1_BIAS    A11 RED_G2    A19 
B20  GRN_BEAM
B21  BLU_BEAM
A13  /VA_OK (/HV_ENA) B19  RED_BEAM
A8         +5.1V
A9          +15V
    A10        -15V
B12   IIC_CLK
B13   IIC_DATA
A12   /IIC_SINTB27  RED_SENS
B26  GRN_SENS B29   OVERLAY
B15   CLAMP
B15   BLANKING
REST ORE   B16  A2    /SEL_VIC#1
B1    /SEL_VIC#2GRN_VIDEO   B4 RED_VIDEO    B2
BLU_VIDEO    B6V_SYNC        A16 H_SYNC        A17
GRN_SYNC  B17
GRN INPUT  A28
A1    /SEL_VIC#3
B32   RED_OVER
B31   GRN_OVER
B30   BLU_OVER
J17
J16
J16
EXTERNAL
VIDEO
FROM
SCB
FROM RTG
FROM
SCB
FROM/
TO VAB
FROM
LVPSTO
RTG
TO
VAB
TO
VAB
TO
VAB
VIDEO
PROCESSOR
BOARD
Figure 2-10.  Video Processor I/O Diagram
IIC Interface
The VPB communicates with the SCB via the IIC bus. The information
transferred over the bus (as shown in Table 2-8) is indicated as follows (I = Input
to the VPB, O = Output from the VPB):
Table 2-8.  Video Processor IIC communication
I/O INFORMATION DESCRIPTION
I RED_CONT Red Contrast level
I GRN_CONT Green Contrast level
I BLU_CONT Blue Contrast level
I BRIGHTNESS Brightness level
I BEAM CURRENT Beam Current 
						

							Chapter 2---System Description
Model 230 Service Manual2-23
I RED_G2 Red G2 Control
I GRN_G2 Green G2 Control
I BLU_G2 Blue G2 Control
I WHT_BOOST Gamma correction
I BLK_BOOST Gamma correction
I G1_BIAS G1 bias level
O /VA_OK Issues to SCB that Video Amplifier
is OK
O BEAM_CURRENT Beam current control
O OK_DETECT Issues to SCB that VPB is OK
Video Processor I/O
This section provides a comprehensive description of the inputs to and outputs
from the VPB. The I/O descriptions in Table 2-9 are arranged by the
source/destination of the signal. The format used is such that the assembly
communicated with is used as the primary heading of each group of signals.
Those signals are further subdivided into inputs and outputs. Inputs refers to an
input to the VPB, while output refers to an output from the VPB.
Table 2-9.  Video Processor I/O signals
SYSTEM CONTROLLER BOARD
INPUT DESCRIPTION
RED_OVER Red signal of on-screen menu and/or internal test pattern
GRN_OVER Similar to RED_OVER
BLU_OVER Similar to RED_OVER
OVERLAY Overlay control signal
RED_SENS Sensitivity correction information for red. Real time data at
0 volt to 1 volt.
GRN_SENS Similar to RED_SENS 
						

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2-24Model 230 Service Manual
BLU_SENS Similar to RED_SENS
RED_THRES Threshold correction information for red. Real time data at
0 Volt to 1 Volt
GRN_THRES Similar to RED_THRES
BLU_THRES Similar to RED_THRES
 I/O DESCRIPTION
IIC_DATA IIC data line. Bidirectional serial line for synchronous data
transfer between SCB and other circuit boards. See detailed
description for list of signals transferred and data direction
IIC_CLK IIC clock line. Unidirectional clock line for  control of
synchronous data transfer over IIC bus.
IIC_INT Interrupt output to SCB
RASTER TIMING GENERATOR
INPUT DESCRIPTION
CLAMP Pulse signal input from the RTG board. Indicates the commanded
timing and duration of the DC restore.
BLANKING Pulse signal input from the RTG board. Indicates the commanded
blanking interval during the scan.
OUTPUT DESCRIPTION
H_SYNC Horizontal sync signal to RTG board
V_SYNC Vertical sync signal to RTG board
GRN_SYNC Green sync signal to RTG board
GRN_INPUT Green video signal to RTG board
VIDEO AMPLIFIER
INPUT DESCRIPTION
RED_BEAM Voltage signal proportional to cathode current averaged
over several horizontal lines in the red CRT. Voltage
level is + mV/mA 
						

							Chapter 2---System Description
Model 230 Service Manual2-25
GRN_BEA Similar to RED_BEAM
BLU_BEA Similar to RED_BEAM
/VA_OK Issued from the VAB to indicate VAB working properly
OUTPUT DESCRIPTION
RED_VID Red video output. 0 Volt to 1 Volt.
GRN_VID Similar to RED_VIDEO
BLU_VIDE Similar to RED_VIDEO
RESTOR DC RESTORE control signal. When this signal is asserted,
DC level of the video signal is clamped at the proper value
on the VAB.
RED_G2 Red CRT G2 voltage adjust control signal.
GRN_G2 Similar to RED_G2
 BLU_G2  Similar to RED_G2
 G1_BIAS  Control the adjustment of G1 voltage for all three CRTs
 EXTERNAL VIDEO
 INPUT  DESCRIPTION
 RED_VIC  Red video input from video input card #1
 GRN_VIC  Similar to RED_VIC #1
 BLU_VIC  Similar to RED_VIC #1
 RED_VIC  Similar to RED_VIC #1
 GRN_VIC  Similar to RED_VIC #1
 BLU_VIC  Similar to RED_VIC #1
 RED_VIC  Similar to RED_VIC #1
 GRN_VIC  Similar to RED_VIC #1
 BLU_VIC  Similar to RED_VIC #1
 H_VIC #1  Horizontal sync signal input from video input card #1
 H_VIC #2  Similar to H_VIC #1
 H_VIC #3  Similar to H_VIC #1
 V_VIC #1 Vertical sync signal input from video input card #1 
						

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2-26Model 230 Service Manual
 V_VIC #2  Similar to V_VIC #1
 V_VIC #3  Similar to V_VIC #1
/SEL_VIC  Input signal from RGB VIC board which is used to select
 input video source from VIC #1.
 /SEL_VIC  Similar to /SEL_VIC #1
 /SEL_VIC  Similar to /SEL_VIC #1
LOW VOLTAGE POWER SUPPLY
INPUTS  DESCRIPTION
+ 5.1 volts  Power supply to digital components
+ 15 Volts  Power supply to analog components
- 15 Volts  Power supply to analog components
2.3.5   Video Amplifier
The Video Amplifier Board (VAB) is located at the back side of the projector
under the necks of the three CRTs. It contains three separate video amplifiers,
one each for red, green, and blue. The outputs from these video amplifiers
connect directly to the CRTs and provide all electrical connections to the CRTS
except for the anode voltages.
The following functions are provided by VAB:
•  Amplification of video signals and driving the cathode of all three
CRTs
•  Sensing the cathode beam current for all three CRTs
•  G1 regulator for all three CRTs
•  Blanking drive section
•  Phosphor protection for all three CRTs
•  G2 regulator and adjustment of black level (screen) for all CRTs
•  DC restoration for the video signals
•  CRT interface for focus, heater voltage and ARC ground
The Video Amplifier Board I/O diagram (Figure 2-11) and the list of Inputs and
Outputs (Table 2-10) provide information for the technician to perform module
level troubleshooting. 
						

							Chapter 2---System Description
Model 230 Service Manual2-27
G1 Regulator for three CRTs
The input supply for the G1 grid of the CRTs is G1_SUPPLY and is about -200V.
The VAB regulates this supply to about -80V to -30V. This supply can be
adjusted by the G1_BIAS line. This adjustment provides the brightness control
function. The G1_BIAS signal is an input of the VAB and is generated by the
Video Processor Board. In the event of a failure, such as lack of deflection (a
high on the /SWEEP_OK line), this output goes to the most negative value of the
input supply (about -200V).
G2 Regulator and  black level adjustment for CRTs
The VAB also regulates the G2 grid of the CRTs. The supply for the G2 grids
(about 1200V) is generated by the HVPS. This G2_SUPPLY is an input to the
VAB. There are also three control inputs (RED_G2, GRN_G2, and BLU_G2).
The G2 voltage of each CRT is adjusted individually by using these control lines.
This adjustment provides black level control. The G2 output voltages are pulled
down during shutdown mode.
RED_VIDEO
GRN_VIDEO
BLU_VIDEO
BLANKING
G1 SUPPLY
G1 BIAS
RESTORE
ARC_GND BLU_CATHODE 8
BLU_GRID1 9
BLU_GRID2 10BLU_BEAM 16
BLU_HEAT- 7 BLU_HEAT+ 6
ARC_GND 3 GRN _CATHODE 8
GRN _GRID1 9
GRN _GRID2 10 GRN_BEAM 14
GRN _HEAT- 7GRN _HEAT+ 6
ARC_GND 3RED _CATHODE  8
RED _GRID1   9
RED _GRID2  10RED_BEAM         12
RED _HEAT-       7 RED _HEAT+   6
ARC _GND    3
2
4
6
23
21
1
2
13      GRN_G2
15      BLU_G2
1     G2 SUPPLY 11      RED_G2
19   /SWEEP_OK
3     + 8OV
7     + 15V
5     + 6.2V
9     -15V
/VA_OK                18
J83 J68
J68
J85
J87 J68
J68
J84-1,
J86-1,
J88-1 J67
J68
J69
J68 From
VPB
From VPB
From HVPSFrom RTG
From VPB
From
VPB
From HVPS
From HVDB
From
LVPS
To  VPB
To  RED
CRT
To  VPB
To  GRN
CRT
To  VPB
To  BLU
CRT
To  VPB
To  
HVPS
VIDEO
AMPLIFIER
BOARD
Figure 2-11.   Video Amplifier PCB, Block Diagram. 
						

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2-28Model 230 Service Manual
CRT interface for Focus, heater voltages and ARC ground
The three CRT sockets are part of the VAB. They provide the necessary
interface for the input of the three CRTs. The Focus voltage for each color is
connected directly to the socket of each CRT.
The VAB provides ARC grounds for each CRT which are used to protect against
arcing of the CRT anode supply.
IIC Interface
The VAB does not use the IIC interface. All adjustments are accomplished by the
control lines coming from the Video Processor Board.
The Video Amplifier Board I/O
This section provides a description of the inputs to and outputs from the VAB.
The I/O descriptions are arranged by the source/destination of the signal. The
assembly communicated with is used as the primary heading of each group of
signals. Those signals are subdivided into inputs and outputs. Input refers to an
Input to the VAB, output refers to an output from the VAB.
Table 2-10.  Video Amplifier I/O signals
VIDEO PROCESSOR BOARD
INPUTS DESCRIPTION
RED_VIDEO
GRN_VIDEO
BLU_VIDEOVideo preamp signals. About 0.5 VPP
G1_BIAS Brightness control line. 0 to 5 V DC
RED_G2
GRN_G2
BLU_G2Black level (G2) control lines 0 to 3.1 V
RESTORE Video DC restoration pulse. logic HC positive going  4% duty cycle
OUTPUTS DESCRIPTION
/VA_OK VAB status line. Low = good VAB. High = Bad VAB (This signal is
called /HV_ENABLE at the HVPS).
RED_BEAM
GRN_BEAM
BLU_BEAMCathode beam current lines. about 1 volt per 100 UA