Hughes JVC Projector 250 Sc Service Manual

Chapter 5---Electronics
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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...

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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...

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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...

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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 -...

Chapter 5---Electronics
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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...

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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...

Chapter 5---Electronics
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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...

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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 =...