Hughes JVC Projector 250 Sc Service Manual

							Chapter 5---Electronics
5-26 Model 250 Service Manual
the V_PARAB waveform. The output waveform V_RGB+ goes to the Scan
Reversal PCB and then drives the Vertical Deflection Yokes. The Vertical
Deflection Yoke return signal to the Horizontal Vertical Deflection PCB is
V_RGB-.
Horizontal Vertical Deflection PCB - Service Adjustments
Vertical Size Adjustment
Tools Needed
Miniature Potentiometer-Trimmer Adjustment tool
To adjust the Vertical height (see Figure 5-15):
1. Remove the rear cover and pull the Interlock switch out to the Service
Mode position.
2. Power ON the projector by IR Remote or PC, and allow it to stabilize for a
minimum of 15 minutes
3. Use the X-hatch test pattern.
 NOTE: The green image is the reference to which the red image and blue
image will be matched. The green height pot should not need adjustment
except when the green CRT has been replaced.
4. Hide Blue and view Red and Green.
5. If Red is higher than Green at the top and lower than Green at the bottom
of the X-hatch image, or If lower than Green at the top and higher at the
bottom, adjust Red vertical pot (R137) to correct the error.
Vertical Adjustment Potentiometers (see Figure 5-15)
Red - R137
Green - R148
Blue - R160
Figure 5-16
  Red image needs vertical adjustment (decrease). 
						

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Model 250 Service Manual 5-27
Figure 5-17  
Red image needs vertical adjustment (increase).
If Red is higher than Green at the top and bottom, or lower than Green at
the top and bottom, the Red image may not being centered correctly. This
can be corrected with the centering adjustment (see Model 250 User’s
Guide, Chapter 5).
Figure 5-18  
Red image needs vertical centering.
If the Red height pot does not completely eliminate the difference in
height between Red and Green, balance the difference at the top and
bottom. Too much of an difference at the top or bottom makes
convergence procedures harder to accomplish.
4. Repeat Steps 2 and 3 above for Blue while hiding Red.
5. Recheck all Geometry and Convergence settings (see User’s Guide) and
readjust wherever necessary. 
						

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Horizontal Vertical Deflection PCB - Remove and Replace
The Horizontal/Vertical (H/V) Deflection PCB is located in the upper portion of
the Electronic Module card cage.
Tools Needed:
#1 Pozi-drive Phillips-head screwdriver
Parts Needed:
Horizontal Vertical Deflection PCB  p/n 105236
To remove the Horizontal/Vertical (H/V) Deflection 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. Remove the rear cover.
4. Disconnect six connectors; J34, J35, J36, J41, J42, and J43 (see Figure
5-15). Move the cables out of the way.
5. Loosen (it is not necessary to remove) the 5 Pozi-drive Phillips-head
screws that secure the Horizontal Vertical Deflection PCB to the
electronic module cage.
6. Remove the Horizontal Vertical Deflection PCB by sliding it toward the
left side of the projector (this is the upward direction if the electronic
module is tilted up) so that the mounting screws clear the access holes.
Then lift the side of the PCB that is nearest the front of the projector first
and angle it upward so that the side closest to the rear clears the lip of the
electronic module frame. Be careful when removing or reinstalling the
PCB to avoid damaging it on the fan screws or cable clamps.
7. Reinstall the Horizontal Vertical Deflection PCB by lowering the side that
is nearest to the rear of the projector in first until it clears the electronic
module edge, then lowering the other side. Carefully fit the board over the
mounting screws and slide the board into position. Tighten the screws and
reconnect the connectors.
5.7  Convergence Deflection PCB
Convergence Deflection PCB - Main Functions
!
 Generation of various waveforms for the horizontal and vertical
deflection.
!
 Height control
!
 Generation of waveforms for dynamic focus
!
 Various geometry correction functions for the horizontal and vertical axes 
						

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Model 250 Service Manual 5-29
!
 Convergence output amplifiers for all colors and both horizontal and
vertical axes
!
 Convergence enable and raster fill function
!
 ILA® assembly driver circuitry with temperature compensation
!
 Phase locked loop for ILA® assembly drivers
!
 IIC serial bus interface
Convergence Deflection PCB - Inputs
X_RGB_CONV - x-axis Convergence waveform from the System Controller
PCB (the amplitude for full-scale correction is about 1 Vpp).
Y_RGB_CONV - y-axis Convergence waveform from the System Controller
PCB (the amplitude for full-scale correction is about 1 Vpp).
CORR_SYNC - square wave from the System Controller PCB, logic level
synchronization signal for the horizontal axis.
V_DRIVE - square wave from the Raster Timing Generator PCB, logic level
synchronized to vertical sync with four horizontal line duty cycle.
WIDTH_CONTROL - a DC waveform from the Horizontal Vertical Deflection
PCB that controls the image width.
IIC_CLK - IIC clock line.
IIC_DATA - IIC data line.
IIC_SINT - IIC interrupt line.
±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.
Convergence Deflection PCB - Outputs
RGB_ILA®(pos) - positive outputs to the ILA® for the red, green, and blue ILA®
driver circuitry (about ±12 Vpp).
RGB_ILA
®(neg) - negative outputs to the ILA® for the red, green, and blue ILA®
driver circuitry (about ±12 Vpp).
H_PARABOLA - horizontal parabola for dynamic focus section of the High
Voltage Power Supply.
V_PARABOLA - vertical parabola for dynamic focus section of the High Voltage
Power Supply.
V_RAMP - vertical ramp waveform to the Horizontal Vertical Deflection PCB
(about 4 Vpp).
V_PARABOLA - vertical parabola waveform to the Horizontal Vertical
Deflection PCB (about 4 Vpp). 
						

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Figure 5-19  
Convergence Deflection PCB I/O Diagram. 
						

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Model 250 Service Manual 5-31
Figure 5-20  
Convergence Deflection PCB I/O Diagram. 
						

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Figure 5-21  
Physical layout of the Convergence/Deflection PCB.
Convergence Deflection PCB  - Operation
The Convergence Deflection PCB performs four main functions. It generates the
vertical deflection sawtooth waveform. It generates the square waves that bias the
three ILA
®s. It controls the amplitude of waveforms used for convergence
corrections, and it generates the parabolic waveform used for dynamic focus.
The Convergence Deflection PCB receives the V_DRIVE signal, which is a
sample of the vertical sync, from the Raster Timing Generator PCB. The
Convergence Deflection PCB has a Waveform Generator Section that generates
the vertical deflection sawtooth waveform and outputs the V_RAMP signal that
drives the vertical amplifier on the Horizontal Vertical Deflection PCB. The
vertical amplifier drives the CRT deflection coils for vertical deflection. The
Waveform Generator also generates the parabolic waveforms used for geometry
correction such as bow, pincushion, keystone, and linearity
Each of the ILA
®s is biased by a square wave generated by the Waveform
Generator on the Convergence Deflection PCB. Each ILA® is biased separately
through the ILA® Bias command in the Factory Adj. Menu. The commands are
received through the IIC interface. As the square wave that drives the ILA® is
increased, the ILA® becomes more sensitive to the image light that strikes the
photoconductive layer and outputs more light. The command that controls the
frequency of the ILA
® bias square wave is referred to as ILA® Sensitivity. It is a
global command for all the ILA®s and is received from the IIC interface.
Attached to the green ILA
® mount is a thermistor that senses the temperature of
the ILA®. It sends the Convergence Deflection PCB a signal that adjusts the green
ILA® bias to compensate for temperature variations inside the projector. If the 
						

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Model 250 Service Manual 5-33
temperature of the green ILA® increases, the bias is increased to maintain a
constant ILA® output.
The Convergence Deflection PCB receives commands for x and y-axis
convergence from the System Controller PCB. The Convergence Deflection PCB
has a Convergence Control Section that receives the convergence commands,
waveforms from the Waveform generator, and geometric correction data from the
IIC interface. It amplifies the convergence data and outputs it to the Scan Reversal
PCB.
The Waveform Generator section generates a horizontal and vertical parabolic
waveforms that the High Voltage Power Supply uses for dynamic focus.
Convergence Deflection PCB - Remove and Replace
The Convergence/Deflection PCB is located on the bottom side of the Electronic
Module card cage (see Figure 5-2).
Tools Needed
#0 Pozi-drive Phillips-head screwdriver
Parts Needed
Convergence Deflection PCB  p/n 105210
To remove the Convergence/Deflection 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. Remove the rear cover.
4. Tilt the Electronic Module up.
5. Disconnect six connectors; J31, J32, J33, J38, J39, and J40 from the
Convergence/Deflection PCB (see Figure 5-21). Move the cables out of
the way.
6. Loosen (it is not necessary to remove) the five Pozi-drive Phillips-head
screws that secure the Convergence Deflection PCB to the Electronics
Module card cage.
7. Remove the Convergence Deflection PCB by sliding it upward so the
mounting screws will clear the access holes, then angle the right side
outward. In order to get the right side of the PCB out, it may be necessary
to first, move the PCB out enough to clear the access holes. Then, angle
the left side out just enough for the top 2 fins of the heat sync to fit over
the Electronics Module frame lip. This will allow a little more clearance
for the right side to be removed. Then, maneuver the right side of the PCB
out. 
						

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5-34 Model 250 Service Manual
8. Reinstall the Convergence/Deflection PCB by lowering the right side in
first  until it clears the electronic module edge, then lowering the left side
in.
NOTE:
 It may be necessary to fit the top 2 fins of the heat sync over the
electronic module frame lip at the left to get enough clearance for the right
side to be installed. Carefully fit the board over the mounting screws and
slide the PCB into position. Tighten the screws and reconnect the
connectors.
5.8  Scan Reversal PCB
Scan Reversal PCB - Main Functions
!
 Reverses of scan in both horizontal and vertical axes
!
 Outputs deflection waveform to the Deflection Yokes on the CRTs
!
 Outputs convergence data to Convergence Yokes on the CRT
!
 Horizontal width adjustment for each color (R, G &B)
!
 Scan failure detection for (horizontal and vertical) deflection amplifiers
Scan Reversal PCB  - Inputs
H_OUT_FLYBACK - output horizontal deflection waveform from the Horizontal
Vertical Deflection PCB (about 800 Vpp).
H_LOCK (pos.) - horizontal interlock for the yoke connectors from the
Horizontal Vertical Deflection PCB (about 5 V when closed, 15 V when open).
H_RGB (pos.) - return of horizontal deflection waveform to the Horizontal
Vertical Deflection PCB.
V_RGB (pos.) - output signals of red, green, and blue from the Vertical Amplifier
of the Horizontal Vertical Deflection PCB (about 40 Vpp).
X_RGB (pos.) - output signals of the red, green, and blue from the Horizontal
Convergence Amplifier for the X-axis from the Convergence Deflection PCB.
Y_RGB (pos.) - output signals of the red, green, and blue from the Horizontal
Convergence Amplifier for the Y-axis from the Convergence Deflection PCB.
±15 V - input power from the Horizontal Vertical Deflection PCB for the analog
circuitry.
+5.1 V - input power from the Horizontal Vertical Deflection PCB for the digital
circuitry.
From Yokes
H_RGB_YOKE (neg.) - bottom of red, green, and blue horizontal deflection
yokes.
V_RGB_YOKE (neg.) - bottom of red, green, and blue vertical deflection yokes.
X_RGB_YOKE (neg.) - bottom of red, green, and blue x-axis convergence yokes. 
						

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Model 250 Service Manual 5-35
Y_RGB_YOKE (neg.) - bottom of red, green, and blue y-axis convergence yokes.
RGB_LOCK (neg.) - interlock for red, green, and blue deflection yokes (5 V
when closed or 0 V when open).
Scan Reversal PCB - Outputs
H_LOCK (neg.) - Horizontal Interlock for the yoke connectors to the Horizontal
Vertical Deflection PCB (about 5 V when closed, 15 V when open).
FRONT/REAR - front or rear projection status line to Horizontal Vertical
Deflection PCB (front = low, rear = high).
FLOOR/CEIL - floor or ceiling status line to the Horizontal Vertical Deflection
PCB (floor = low, ceiling = high).
DEFL_OK - deflection status line from the Horizontal Vertical Deflection PCB
(high (about 2 V) = good, low = no scan).
X_RGB(neg) - current feedback signals of the red, green, and blue Horizontal
Convergence Amplifier for the x-axis to the Convergence Deflection PCB.
Y_RGB (neg.) - current feedback signals of the red, green, and blue Horizontal
Convergence Amplifier for the y-axis to the Convergence Deflection PCB.
To Yokes
H_RGB_YOKE (pos.) - top of red, green, and blue horizontal deflection yokes.
V_RGB_YOKE (pos.)  - top of red, green, and blue vertical deflection yokes.
RGB_LOCK (pos.) - interlock for red, green, and blue yokes (5 V when closed or
15 V when open).
X_RGB_YOKE (pos.) - top of red, green, and blue x-axis convergence yokes.
Y_RGB_YOKE (pos.) - top of red, green, and blue y-axis convergence yokes.