Hughes JVC Projector 250 Sc Service Manual

							Chapter 5---Electronics
5-16 Model 250 Service Manual
6. Pull the black card extractor handles back to disconnect the Video
Processor PCB connector and pull the PCB out of the Electronics Module.
7. Reverse the procedure to install the Video Processor PCB.
5.5  Raster Timing Generator PCB
Raster Timing Generator PCB - Main Functions
!
 Generates an internal sync pulse
!
 Detects and selects sync pulses
!
 Generates a phase locked sync
!
 Generates blanking pulse
!
 Provides horizontal and vertical phase adjustments
!
 Detects interlaced and generates odd field pulse
!
 Selects horizontal frequency band
!
 Generates horizontal line count and vertical count
!
 Provides IIC interface
!
 Generates clamp pulse
!
 Detects changes in source
!
 Generates HVPS_SYNC signal
!
 Enables horizontal deflection (/H_ENA) circuitry
Figure 5-10  
Raster Timing Generator I/O diagram for Power Supplies. 
						

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Model 250 Service Manual 5-17
Figure 5-11  
Raster Timing Generator for other PCBs.
Raster Timing Generator PCB - Inputs
V_SYNC - input vertical sync from the Video Processor PCB.
H_SYNC - input horizontal sync from the Video Processor PCB.
G_SYNC - Sync-on-Green sync stripped from green video signal at the Video
Processor PCB.
ISYNC - 5 MHz clock from the System Controller PCB used to generate the
internal sync. 
						

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IIC_CLK - IIC clock line. Unidirectional clock line for control of synchronous
data transfer over the IIC bus.
IIC_DATA - IIC data line. Bi-directional serial line for synchronous data transfer
between System Controller PCB and Raster Timing Generator PCB.
+15 V (two inputs) - input power from LVPS for analog circuitry including the
Phase Lock Loop (PLL) circuit.
-15 V (two inputs) - input power from LVPS for analog circuitry including the
Phase Lock Loop (PLL) circuit.
+5.1 V - input power from the LVPS for digital circuitry
Raster Timing Generator PCB - Outputs
SOURCE_VALID - signal to the System Controller PCB, indicates a new or valid
source. High = valid, stable source, low = change in input source.
ODD_FIELD - square wave to System Controller PCB, with 50% duty cycle that
is high during the odd field of an interlaced signal and low for non-interlaced
signals.
280_CLK - square wave to System Controller 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.
CLAMP - a negative-going image clamp signal to the Video Processor PCB, with
about 3% duty cycle.
BLANKING - right, left, top, and bottom blanking signal to the Video Processor
PCB.
H_BAND(0-3) - horizontal frequency band lines to the Horizontal Vertical
Deflection PCB.
Band 0 = 15 - 24 kHz
Band 1 = 24 - 28 kHz
Band 2 = 28 - 55 kHz
Band 3 = 56 - 90 kHz
/H_ENA - enables the horizontal deflection amplifier on the Horizontal Vertical
Deflection PCB, Low = enabled deflection; high = disabled deflection.
H_FV2 - a DC voltage to the Horizontal Vertical Deflection PCB and System
Controller PCB, proportional to horizontal frequency.
H_DRIVE - square wave to the Horizontal Vertical Deflection PCB, 50% duty
cycle synchronized to the selected horizontal sync. This signal provides a sample
of the horizontal sync to the horizontal amplifier on the Horizontal Vertical
Deflection PCB.
HVPS_SYNC - synchronization pulse for High Voltage Power Supply,
synchronized with the selected horizontal sync at the same, half, or one third the
frequency. 
						

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Model 250 Service Manual 5-19
V_DRIVE - square wave negative going pulse to the Convergence Deflection
PCB, synchronized to the selected vertical sync with the pulse width of about four
horizontal periods.
Raster Timing Generator PCB - Operation
The Raster Timing Generator PCB generates a square wave that is phase-locked
to the horizontal sync pulse. It generates timing signals such as Blanking that goes
to the Video Processor PCB and Video Amplifier PCB, and the H_DRIVE signal
that goes to the Horizontal Vertical Deflection PCB. The PLL (Phase Locked
Loop) locks these signals to the horizontal sync signal. The Raster Timing
Generator PCB has LEDs that indicate the type of sync pulse received and the
status of the PLL circuit (see Figure 5-12).
The H_DRIVE signal supplies a sample of the horizontal scan frequency to the
horizontal deflection amplifier on the Horizontal Vertical Deflection PCB for
timing of the horizontal deflection waveform.
The Raster Timing Generator PCB checks the incoming syncs to make sure they
are valid signals and within the frequency ranges (15 - 90 kHz - horizontal, and 45
- 120 Hz vertical). If the syncs are out of range, or there is no sync pulse, the
Raster Timing Generator PCB generates an internal interlaced sync at 33.7 kHz
horizontal and 60 Hz vertical.
The Raster Timing Generator PCB tells the System Controller PCB when there
has been a source change using the SOURCE_VALID signal.
The Raster Timing Generator PCB generates the Blanking signal, and the
horizontal Phase signal.
!
 Blanking shuts off the image during times where there is no active video. The
Blanking signal pulls the G1 voltage on the Video Amplifier PCB down far
enough to make the CRT shut off. The Raster Timing Generator PCB receives
the top, bottom, left, or right blanking command on the IIC bus and sends the
appropriate Blanking signal to the Video Processor PCB.  The Raster Timing
Generator PCB receives the Blanking adjustment commands on the IIC bus.
!
 The horizontal Phase signal adjusts the on-screen image horizontally to
compensate for different phase requirements at different horizontal scan
frequencies. The Raster Timing Generator PCB receives this command from
the System Controller PCB on the IIC bus.
The Raster Timing Generator PCB sends several signals such as 280_CLOCK
signal to the System Controller PCB to correctly set the timing for shading and
convergence data.
In order to combat noise caused by crosstalk between supplies (beat patterns) the
High Voltage Power Supply is phase locked to the incoming horizontal frequency
by the HVPS_SYNC signal.
The horizontal flyback time gets shorter as the horizontal scan frequency
increases.  The Raster Timing Generator PCB works together with the Horizontal 
						

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5-20 Model 250 Service Manual
Vertical Deflection PCB to break the range of horizontal scan frequencies into
four smaller ranges called bands (see Figure 5-12).
Figure 5-12  
LEDs on the Raster Timing Generator PCB.
Raster Timing Generator PCB - Remove and Replace
Tools Needed
#1 Pozi-drive Phillips-head screwdriver
Parts Needed
Raster Timing Generator PCB - p/n 105238
To remove the Raster Timing Generator 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. Pull the black Card Extractor handles back to disconnect the Raster
Timing Generator PCB connector and pull the PCB out of the Electronics
Module.
7. Reverse the procedure to install the Raster Timing Generator PCB. 
						

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Model 250 Service Manual 5-21
5.6  Horizontal Vertical Deflection PCB
Horizontal Vertical Deflection PCB - Main Functions
!
 Drive the main horizontal deflection coils to provide horizontal raster scan
for the CRTs
!
 Drive main vertical coils to provide vertical raster scan for the CRTs
!
 Horizontal raster centering for all three colors
!
 Switch mode power supply generating the required proportional DC
supply
!
 Horizontal width adjustment
!
 Horizontal retrace switch network
!
 Left/right pincushion and keystone correction
!
 Vertical linearity adjustments individually for all three colors.
!
 Vertical raster centering for all three colors
!
 IIC interface.
Horizontal Vertical Deflection PCB - Inputs
H_BAND:0-3 - horizontal scan frequency bands, from Raster Timing Generator
PCB.
/H_ENABLE - from the Raster Timing Generator PCB, enables the horizontal
deflection supply. Low = enabled deflection, High = disabled deflection.
H_DRIVE - square wave from the Raster Timing Generator PCB, 50% duty cycle
synchronized to the selected horizontal sync.
H_F2V - a DC voltage from the Raster Timing Generator PCB, proportional to
horizontal frequency
H_LOCK (neg.) - Deflection Yoke Connector Interlock return from the Scan
Reversal PCB.
DEFL_OK - deflection status signal from the Scan Reversal PCB (high = good,
(about 2 V), low = no scan).
V_RAMP - vertical ramp waveform from the Convergence Deflection PCB,
(about 4 Vpp).
V_PARAB - vertical parabola waveform from the Convergence Deflection PCB,
(about 4 Vpp).
FRONT/REAR - front or rear projection status line from the Scan Reversal PCB.
(FRONT = low, REAR = high).
FLOOR/CEILING - floor or ceiling projection status line from the Scan Reversal
PCB. (FLOOR = low, CEILING = high). 
						

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IIC_CLK - IIC clock line
IIC_DATA - IIC data line
IIC_SINT - IIC interrupt
±15 V - input power from the Low Voltage Power Supply, for the analog
circuitry.
+5.1 V - input power from the Low Voltage Power Supply, for the digital
circuitry.
Figure 5-13  
Horizontal/Vertical I/O Diagram. 
						

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Model 250 Service Manual 5-23
Figure 5-14  
Horizontal/Vertical I/O Diagram for Scan Reversal and Video
Amplifier PCBs. 
						

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Figure 5-15  
Physical layout of the Horizontal/Vertical PCB (note the Vertical Size
Adjustment Pots (Red-137, Grn-148, and Blu-160) on  the lower right).
Horizontal Vertical Deflection PCB - Outputs
/SWEEP_OK - signal to the Video Amplifier PCB, derived from the H_ENA
signal from the Raster Timing Generator PCB, and the DEFL_OK from the Scan
Reversal PCB.
WIDTH_CTRL - a DC voltage to the Convergence Deflection PCB that adjusts
the parabola waveforms used for geometric correction (about 4 V max.).
H_RGB(pos.) - horizontal deflection waveform return from the Scan Reversal
PCB. A DC offset that shifts the reference for red, green, and blue image for
centering.
H_OUT_FLYB - output waveform to the Scan Reversal PCB for the horizontal
deflection coils on the CRTs.
H_LOCK (pos.) - +15 V to the Scan Reversal PCB for deflection yoke connector
interlock.
V_RGB (pos.) - positive vertical deflection voltage to the Scan Reversal PCB.
V_RGB (neg.) - negative vertical deflection voltage to Scan Reversal PCB.
±15 V - pass through voltage from Low Voltage Power Supply to Scan Reversal
PCB to power analog circuitry.
+5.1 V - pass through voltage from Low Voltage Power Supply to Scan Reversal
PCB to power digital circuitry.
H_CUR_FDBK - current feedback to horizontal waveform amplifier.Vertical Adjustment Pots 
						

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Horizontal Vertical Deflection PCB - Operation
The Horizontal Vertical Deflection PCB consists of a RGB horizontal deflection
amplifier and separate vertical deflection amplifiers.
The Horizontal Deflection Amplifier
The horizontal deflection amplifier is a switching mode power supply that varies
according to the input horizontal sync frequency. The horizontal supply generates
the sawtooth current-driven waveform that drives the horizontal deflection coils
on the CRT. The sawtooth current waveform creates the raster on the CRT. The
horizontal amplifier also generates the retrace waveform portion of the raster.
The horizontal deflection sawtooth waveform is modulated by other waveforms
that perform geometric correction such as Pincushion, Keystone, Horizontal
Centering, Horizontal Linearity and Horizontal Width adjustment. The Width
Control voltage also goes to the Convergence Deflection PCB to adjust the
geometric correction parabolas.
The H_F2V signal converts the input horizontal scan frequency to a voltage that
switches from one band (see explanation of bands in the Raster Timing Generator
PCB Operation section) to the next depending on the horizontal scan frequency.
This adjusts the retrace time to correspond to the input horizontal frequency. The
output of the horizontal supply is H_OUT_SUPPLY that goes on to the Scan
Reversal PCB.
CRT Protection
The Horizontal Vertical Deflection PCB uses the H_LOCK+, H_LOCK- and
DEFL_OK signal to protect the CRTs from being damaged if the deflection
waveforms are lost. Refer to the CRT Protection section in Chapter 9 for a
complete discussion of these and all the signals associated with CRT Protection.
The Horizontal Vertical Deflection PCB receives the DEFL_OK signal from the
Scan Reversal PCB indicating the presence of the horizontal and vertical
deflection waveforms. If there is a failure of any of the Deflection Yokes
(horizontal or vertical), a current sense line on the Scan Reversal PCB forces
DEFL_OK low. On the Horizontal Vertical Deflection PCB, the DEFL_OK
signal becomes /SWEEP_OK and is sent to the Video Amplifier PCB where it
shuts down G
1. If DEFL_Ok is forced low, or if /H_ENA is forced high,
/SWEEP_OK goes high. The /SWEEP_OK goes to the Video Amplifier PCB. If it
goes high, it shuts down the G
1 voltages and G2 Regulator circuit (see
Troubleshooting, CRT Protection section).
Vertical Deflection Amplifier
The vertical deflection sawtooth waveform is generated on the Convergence
Deflection PCB and timed to the vertical sync by the V_DRIVE signal from the
Raster Timing Generator PCB. The Convergence Deflection PCB sends this
waveform along with a parabola waveform V_PARAB to the vertical deflection
amplifier on the Horizontal Vertical Deflection PCB. The Horizontal Vertical
Deflection PCB takes V_RAMP, amplifies it and adds geometric correction with