Hughes JVC Projector 250 Service Manual

							Chapter 5---Electronics
5-36 Model 250 Service Manual
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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5-38 Model 250 Service Manual
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 for reversing the projection mode
from front to rear projection and from upright to inverted (upside down) mounting
projection setups. The projection modes are changed by switching a jumper from
one connector to another on the Scan Reversal PCB. J100 and J101 are for
horizontal scan connections. J53 and J53A are the vertical scan connections, and
J50 and J50A are convergence jumper connections. The Model 250 comes set for 
						

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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, which sends
the signals back to the System Controller PCB through the IIC data bus. This
allows the System Controller PCB to properly output convergence and shading
data, however the shading, convergence, geometry will need to be adjusted after
switching deflection modes.
The Scan Reversal PCB receives the deflection waveforms from the Horizontal
Vertical Deflection PCB. The horizontal deflection waveforms go through the
horizontal size adjustment inductors (L1, L2, and L3) and is output to the
Deflection Yokes on the CRT without any further signal processing. The vertical
deflection waveforms pass through the Scan Reversal PCB without any further
signal processing. The convergence data passes through the Scan Reversal PCB to
the Convergence Yokes on the CRT without any further signal processing.
The Scan Reversal PCB provides for the adjustment of horizontal scan width.
Inductor L1 adjusts the red horizontal width, and L5 adjusts the blue horizontal
width. L3 increases the horizontal size range of red and blue.
The Scan Reversal PCB contains two major components of the CRT Protection
circuit. The first component is the DEFL_OK signal that goes back to the
Horizontal Vertical Deflection PCB. The Scan Reversal PCB has a sensing
inductor (coil) that detects the presence of a horizontal and vertical deflection
waveform for each CRT. These sense lines combine to drive the DEFL_OK
signal. If any of the deflection waveforms are not present, the DEFL_OK signal
goes low. As the /SWEEP_OK signal it shuts down the G
1 and G2 regulator
voltages on the Video Amplifier PCB. It also shuts down the high voltage section
of the High Voltage Power Supply (see CRT Protection section of Ch. 7--
Troubleshooting).
The other component of the CRT Protection circuit on the Scan Reversal PCB is
the H_LOCK+ and H-LOCK- signals. These signals are actually one voltage (+15
V) that forms a series circuit through each vertical and horizontal deflection yoke
connector on each CRT. If any of the deflection yokes are not properly or
securely installed, the H_LOCK- signal shuts down the horizontal amplifier on
the Horizontal Vertical Deflection PCB (see CRT Protection section of Ch. 7--
Troubleshooting). 
						

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5-40 Model 250 Service Manual
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.
5. Power ON the projector by IR Remote or PC, and allow it to stabilize for a
minimum of 15 minutes
6. Use the X-hatch test pattern.
7. Hide Blue. View Red and Green.
8. If the Red image is outside the Green image on both sides, or inside the
Green image on both sides, use a Delrin .100 hex alignment tool to adjust
the Red horizontal size coil to correct the error. If the Red image is outside
the Green image on one side and inside of Green on the other side, this is
most likely caused by Red not being centered correctly and can be
corrected with the centering adjustment (User’s Guide, Chapter 5).
If the Red horizontal size coil does not completely eliminate the size error
between Red and Green, balance the difference on both sides to allow for
easier convergence.
9. Repeat Steps 4 and 5 above for Blue while hiding Red. 
						

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Model 250 Service Manual 5-41
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. The projector must be powered OFF when Scan
Reversal Jumpers are being changed.
Front/Rear Jumper Setting (Horizontal Reverse)
!
 The Horizontal Scan Reversal Jumper reverses the image projection for
front or rear projection. Figure 5-25 illustrates the jumpers’ location on the
Scan Reversal Board.
!
 The Model 250 Projector is shipped with the jumper plugs inserted in J50
and J100 for front/upright projection (see Table 5-1 for other
orientations).
To set the Horizontal Scan Jumper:
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. Verify that the Horizontal Scan Reversal jumper is plugged into J100 and
the convergence jumper is plugged into J50 for front projection (see
Figure 5-25 and Table 5-1).
5. Switch the Horizontal Scan Reversal jumper to J101 and the Convergence
Jumper to JA50 for rear projection (see Figure 5-25 and Table 5-1).
6. Replace the projector cover.
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. Recheck centering, convergence, and shading when changing jumpers for
front or rear screen projection. 
						

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5-42 Model 250 Service Manual
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 Jumper Setting
The Ceiling/Floor jumpers invert the image vertically for use in some situations
that use dual mirror projection setups.
  CAUTION! The Model 250 Projector can not be
mounted in the inverted (upside down) position, 
however there are
dual mirror applications where the vertical scan jumper will need to be
changed to the inverted setting (JA53).
Figure 5-21 illustrates the location of the jumpers on the Scan Reversal Board.
The Model 250 Projector is shipped in the normal vertical projection position with
the jumper plug inserted into J53. For an inverted vertical setup this jumper plug
must be inserted into JA53. (see Table 5-1 for other orientations).
To invert the vertical image:
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. Verify that the Vertical Scan Jumper is plugged into J53 for upright
projection. (see Figure 5-25 and Table 5-1).
5. Switch the Vertical Scan Jumper to JA53 for inverted projection. The
Convergence Jumper will not need to be changed for inverted projection
unless the Horizontal Scan Jumper is being changed.
6. Replace the rear cover. 
						

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Model 250 Service Manual 5-43
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 Needed
#1 Pozi-drive Phillips-head screwdriver
Parts Needed
Scan Reversal PCB  p/n 102585
To remove the Scan Reversal 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 projector rear cover.
4. Disconnect seven connectors (seeFigure 5-25): J52, J54, J64, J65, J66, J50
(or J50A), and J100 (or J101). To remove, push in slightly, squeeze the
tabs, and then pull connector out.
5. Move all cables out of the way.
6. Remove the four Pozi-drive screws (see Figure 5-25) and lift the board off
the Electronics Module.
7. Reinstall in the reverse order from above.
5.9 Video Amplifier PCB
Video Amplifier PCB - Main Functions
!
 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 
						

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5-44 Model 250 Service Manual
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 lines from Video Processor PCB (0-3.1 V).
G
2_SUPPLY - supply for G2 grid on CRTs from High Voltage Power Supply
(about 1200 V).
RGB_ FOCUS - Focus supply for CRTs from the High Voltage Power Supply
(approximately 7 kV).
SWEEP_OK - deflection status line from the Horizontal Vertical Deflection PCB.
+80 V - from the Low Voltage Power Supply
±15 V - input power for the analog circuitry from the Low Voltage Power Supply.
6.2 V - input power for the CRT filaments heaters from the Low Voltage Power
Supply. 
						

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Model 250 Service Manual 5-45
Figure 5-26  
Video Amplifier PCB I/O Diagram