Hughes JVC Projector 250 Service Manual

Chapter 5---Electronics
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Figure 5-22  
Scan Reversal PCB I/O Diagram. 

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Model 250 Service Manual 5-37
Figure 5-23  
Scan Reversal PCB I/O Diagram for Horizontal Vertical Deflection PCB. 

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Figure 5-24  
Scan Reversal PCB I/O Diagram for CRT Yokes.
Scan Reversal PCB - Operation
The Scan Reversal PCB has several functions. It provides an interface for scan
reversal, and provides for horizontal width adjustment. The Scan Reversal PCB
outputs the convergence and deflection waveforms that drive the CRT
convergence and deflection yokes, and it contributes significantly to the CRT
Protection circuit.
The Scan Reversal PCB provides an interface...

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Model 250 Service Manual 5-39
front/upright projection. This means the horizontal scan jumper is plugged into
J100, the vertical scan jumper is plugged into J53, and the convergence jumper is
plugged into J50.
NOTE:
 Whenever the horizontal scan jumper is switched from front projection to
rear projection, the convergence must also be switched from J50 to J50A.
The Scan Reversal PCB sends two signals (FRONT/REAR and
FLOOR/CEILING) back to the Horizontal Vertical Deflection PCB,...

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Scan Reversal PCB - Service Adjustments
Figure 5-25  
Physical layout of the Scan Reversal PCB.
Horizontal Size adjustment
The Horizontal size adjustment must be performed after the Horizontal Vertical
Deflection PCB is replaced.
Tools Needed
Delrin .100 hex alignment tool
Equipment Needed
No equipment needed
To adjust the horizontal size coils (see Figure 5-25):
4. Remove the rear cover and pull the Interlock switch out to the Service
Mode position....

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10. Recheck all Geometry and Convergence settings and readjust wherever
necessary.
11. Replace the rear cover.
Front/Rear Projection Jumper Settings
In the procedures below each of the jumpers mentioned have a specific purpose:
J100 and J101 are the horizontal scanning jumpers, J 53 and J53A are the vertical
scanning jumpers, and J50 and J50A are the convergence jumpers.
  CAUTION!  Do not attempt to switch jumpers while the
projector is operating....

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Table 5-1  
Projection orientation jumper settings.
OrientationConvergence.
P50 goes to:Vertical.
P53 goes to:Horizontal.
P100 goes to:
Front/Floor
(Upright)J50 J53 J100
Front/Inverted*
JA50 JA53 J101
Rear/Floor
(Upright)JA50 J53 J101
Rear/Inverted*
J50 JA53 J100
* see CAUTION! below
NOTE: Whenever the horizontal scan jumper is switched from front projection to
rear projection, the convergence must also be switched from J50 to J50A.
Floor/Ceiling...

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7. Power ON the projector and allow it to stabilize for a minimum of 15
minutes. It is recommended that the projector be operating for a least one
hour before performing shading adjustments.
8. When changing jumpers for floor or ceiling screen projection, Centering,
Convergence and Shading must be rechecked.
Scan Reversal PCB - Remove and Replace
The Scan Reversal PCB is located on the front side of the Electronic Module (see
Figure 5-2).
Tools...

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Video Amplifier PCB  - Inputs
RGB_VIDEO - image pre-amp signals from the Video Processor PCB (about 0.5
Vpp).
RESTORE - image DC restorations pulse from Video Processor PCB, logic level
positive going 4% duty cycle.
BLANKING - Blanking signal, logic F type.
G
1_SUPPLY - supply for G1 grid on CRTs from High Voltage Power Supply
(about -150 V).
G
1_BIAS - brightness control line from Video Processor PCB (0-5 VDC).
RGB_G
2 - G2 (black level) control...

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Figure 5-26  
Video Amplifier PCB I/O Diagram