Hughes JVC Projector 250 Sc Service Manual

							Chapter 7---Troubleshooting
Model 250 Service Manual 7-3
Figure 7-1  Rear Panel layout
Control Out -  The Control Out terminal is another RS232 port similar to the
Terminal In port except that it can not be used to Import/Export setup data.
Tethered Remote Jack - The Model 250 projector is shipped with an IR Remote
Control. This IR Remote can be used with an optional 150 ft. cable that will plug
in the Tethered Remote Jack.
IR Detector - This sensor detects commands from the IR Remote Control included
with the projector. There is another IR Detector on the front of the projector.
Switch Block - The Switch Block controls various parameters of the CPU. Most
of the switches are for diagnostic functions performed at the factory and will not
need to be changed. They should all be in the DOWN position. The switch that
will be of most concern to the field technician is the #4 switch that controls the
baud rate of importing and exporting data and software. The UP position sets the
baud rate at 19200 BPS and the DOWN position is 9600 BPS. 9600 BPS
(DOWN) is the factory default setting. 
						

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Figure 7-2  
Dip Switch Block  on System Controller PCB.
Reset Switch - The Reset Switch resets the CPU if the projector locks up and does
not respond to an IR Remote, PC or Laptop computer. If the rear panel is in place,
the CPU can also be reset by cycling the AC Circuit Breaker off and back on
again.
  CAUTION!  If the Arc Lamp was operating or recently
turned off (the cooling fans were still running) at the time the CPU
locked up, it is very important to turn the AC Circuit Breaker back on
immediately to power ON the cooling fans. The cooling fans are
needed to cool down the Arc Lamp, Optics and PCBs properly to avoid
damage to optical and electronic components.
If the Reset Switch is used, the cooling fans will stop momentarily and
begin operating again automatically.
Figure 7-3  
LEDs visible from the left side of the Electronics Module.
For a complete description on each of the LEDs, check the individual PCBs LEDs
in this section. 
						

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Video Processor PCB LEDs
Figure 7-4  
Video Processor Test Points and LEDs.
Video Processor - Test Points
The test points on the Video Processor PCB are visible and accessible from the
left side of the Electronics Module when the rear projector cover is removed. The
test points can be grouped into four categories: 
						

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Sync - There are three sync test points: H sync for the horizontal sync pulse, V
sync for the vertical sync pulse, and G sync, which is a combination of the
horizontal and vertical sync pulses that are carried with the green image signal.
External - There are three external image test points: R ext, for the red external
image signal, G ext for the green external image signal, and B ext for the blue
external image signal. The external signal is the image signal coming into the
Video Processor PCB from the VIC.
Figure 7-5  
Grey/Pluge (test pattern #7) with associated waveform.
Video - There are three video test points: R video for the red output image signal,
G video for the green output image signal, and B video for the blue output image
signal. The video signal is the image signal leaving the Video Processor PCB and
going to the Video Amplifier PCB.
Ground - The Gnd test point is for reference ground.
The other test point on the Video Processor PCB is for the /Clamp signal, which is
not very useful for troubleshooting purposes.
Video Processor - LEDs
The Video Processor PCB has two green LEDs. VP_OK is a status line that
indicates that the Video Processor PCB is has power (±15 V). The Beam current
LED will be illuminated orange if any of the CRTs is at or exceeding beam
current limit (250 µ A). If any of the CRTs is at the beam current limit, the Video
Processor will reduce Contrast. If reducing Contrast does not bring down the
beam current for that CRT, the Video Processor PCB will reduce G2 voltage. 
						

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Raster Timing Generator PCB LEDs
Figure 7-6  
 Raster Timing Generator LEDs. 
						

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Raster Timing Generator PCB LEDs
Band LEDs
 The range horizontal scan frequencies accepted by the Model 250 projector is
divided into four “bands”. The four LEDs  (A, B, C, & D) toward the front of the
projector on the Raster Timing Generator PCB indicate which range of horizontal
scan frequencies the input source is operating. The four bands of horizontal
frequencies are
Band A = 15-25 kHz
Band B = 26-29 kHz
Band C = 29-56 kHz
Band D = 56-90 kHz
Only one of these LEDs will be illuminated green at one time. As an example, if
the input source horizontal scan frequency is 64 kHz, Band D LED would be
illuminated green.
Sync Type LEDs
The five LEDs, toward the rear of the projector on the Raster Timing Generator
PCB, indicate the sync of the input source. As an example, the SEP LED would
be illuminated green if the input source had separate horizontal and vertical syncs.
The following list gives a brief description of the each LED and its associated
sync type.
SEP - Separate horizontal and vertical sync inputs.
COMP -Composite (Red, Green, Blue, Horizontal, and Vertical signals all
combined into one signal).
INT - Internal sync means there is no input source sync signal present so the
System Controller PCB generates an internal sync at a horizontal scan rate of
33.7 kHz and a vertical rate of 59.7 Hz interlaced.
GRN - Sync-on-Green sync is where the horizontal and vertical sync signals are
combined with the green image signal.
PLL - Phase Locked Loop is the circuitry that locks onto the horizontal sync. This
LED indicates that the projector has locked onto the horizontal sync signal.
One of the first four LEDs should be illuminated indicating the type of sync used
by the input source. The fifth LED (PLL) should always be illuminated when the
projector is operating except during input source changes. 
						

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Convergence Deflection PCB LED
Figure 7-7  
Convergence Deflection PCB LED.
The Convergence Deflection PCB has only one LED. It illuminates green when
power (±15 V) is present on the PCB. 
						

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Video Amplifier PCB LED
Figure 7-8
  Video Amplifier PCB LED.
The VA_OK LED on the Video Amplifier PCB is illuminated green when all the
CRT deflection circuits are operating properly (/DEFL_OK), the supply voltages
(±15 V, +6.2 V, and +80 V)  are present at the Video Amplifier PCB, and all the
CRT Yoke connectors are properly installed (see Figure 7-15 and Figure 7-16). 
						

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Backplane PCB LEDs
Figure 7-9  
Backplane PCB LEDs on right side (exposed side)of PCB.
The Backplane has two status LEDs, the /LV_OK signal from the Low Voltage
Power Supply, and the /HV_OK signal from the High Voltage Power Supply. The
Backplane also has several connectors that can be used for probing signals and
voltages (see Figure 7-18 and associated signals and voltages). 
						

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7.3 Diagrams
Command ON Timing
Figure 7-10  
POWER ON and POWER OFF command timing diagram.
When the AC Circuit Breaker is powered ON, the Low Voltage Power Supply
generates a +5.1 V Standby voltage that goes to the System Controller PCB to
power the CPU and IR Detectors. The Low Voltage Power Supply also puts out
the +24 V Standby voltage (/FAN_ENA goes low) that provides power to the
cooling fans. The cooling fans run from the time the AC Circuit Breaker is
powered ON until approximately ten minutes after the projector receives a power
Off command (AC Circuit Breaker still on).
When the projector receives a power ON command from the IR Remote, PC or
Laptop, the System Controller PCB receives a /LAMP_OK from the Arc Lamp
Power Supply.  The System Controller PCB then drives the /LAMP_ENA signal