Hughes JVC Projector 250 Service Manual

Chapter 3---Electrical
Model 250 Service Manual 3-5
!
 +5.1V for digital components
!
 +6.2V for CRT filaments
!
 ±15V for analog circuits
!
 +80V supply used by the High Voltage Power Supply, Video Amplifier
PCB, and the Horizontal/Vertical Deflection PCB.
LVPS - Service Adjustments
There are no service adjustments for the Low Voltage Power Supply.
LVPS - Remove and Replace
Tools Needed:
#2 Posi-drive Phillips-head screwdriver
Parts Needed:
Low Voltage Power Supply - p/n 102520
To remove the Low Voltage...

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Model 250 Service Manual
ALPS - Inputs:
AC input power: Directly from the AC Line Filter. The input range is from 220-
240 VAC, at 50/60 Hz.
/LAMP_ENA - from the System Controller PCB. Turns on the ALPS.
/COVER_ON - signal enabling the Arc Lamp Power Supply.
/LAMP_OK  - the input is jumpered at the Arc Lamp Power Supply (tied to
ground) so it is always low.
/ = Active Low
ALPS - Outputs:
!
 +170 VDC output during the boost phase to get Arc Lamp ignition. This
supplies the...

Chapter 3---Electrical
Model 250 Service Manual 3-7
Figure 3-2  
Arc Lamp Power Supply signals and voltages.
ALPS - Operation:
Three signals (/LAMP_ENA, /COVER_ON, and /LAMP_OK) are required in
order for the Arc Lamp Power Supply to light the Arc Lamp. The /LAMP_OK
(active low) input is jumpered to ground at the Arc Lamp Power Supply, so it is
always low. The Arc Lamp Power Supply sends the /LAMP_OK to the System
Controller PCB. The System Controller PCB then sends the /LAMP_ENA signal
back to the Arc...

Chapter 3---Electrical
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Model 250 Service Manual
The Arc Lamp Power Supply sends the
/LAMP_LIT signal back to the System Controller when the Arc Lamp is lit.
The Arc Lamp regulates its output to give a constant Arc Lamp power. If the Arc
Lamp has not lit within 20 seconds (/LAMP_LIT still high), the System
Controller PCB will try once more to re-initiate the sequence. If the Arc Lamp
still fails to light, an error code will appear on the back panel (see section 7.22
Error Codes).
The Arc Lamp Power...

Chapter 3---Electrical
Model 250 Service Manual 3-9
2. Turn the AC Circuit Breaker to the OFF position and unplug the AC
Power Cord.
3. Remove the front cover (see section 6.1 Projector Covers ).
4. Remove the lower-right-side panel by removing the five Pozi-drive screws
securing it.
5. Remove the five Pozi-drive screws securing the EMI Shield. Slide the
shield to the left and remove it.
6. Disconnect the INPUT AC plug.
7. Disconnect the two CONTROL SIGNALS cables. The /LAMP_OK signal
jumper is attached...

Chapter 3---Electrical
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Model 250 Service Manual
Figure 3-4  
High Voltage Power Supply I/O signals.
HVPS - Inputs
HVPS_SYNC - this signal is generated on the Raster Timing Generator PCB.
Square wave HCT level with 50 or 33% duty cycle. The signal is synchronized to
horizontal sync.
/HV_ENA - The HVPS shutdown signal from the Video Amplifier PCB
(/VA_OK).
H_PARABOLA - The horizontal parabola from the Convergence Deflection PCB
used by the Dynamic Focus Amplifier.
V_PARABOLA  - The vertical parabola...

Chapter 3---Electrical
Model 250 Service Manual 3-11
RGB Anode Voltage - goes directly to each CRT
RGB Focus Voltage - goes directly to each CRT
Arc Ground - The Arc Ground protection for each CRT from the Video Amplifier
PCB.
HVPS - Operation
The High Voltage Power Supply has three basic functions.
!
 High Voltage Generation
!
 Focus Voltages
!
 High Voltage and CRT Protection
High Voltage Generation - The High Voltage Amplifier section converts the +80
V from the Low Voltage Power Supply, to 25 kV, and...

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Model 250 Service Manual
HVPS - Remove and Replace
Tools Needed
#1 Pozi-drive Phillips-head screwdriver
#2 Pozi-drive Phillips-head screwdriver
small Flathead screwdriver
Parts Needed
High Voltage Power Supply  p/n 102566
To remove the High Voltage Power Supply:
1. Power off the projector by IR Remote or PC, and allow the cooling fans to
run until they shut off.
2. Turn the AC Circuit Breaker to the OFF position and unplug the AC
Power Cord.
3. Remove the front cover.
4....

Chapter 3---Electrical
Model 250 Service Manual 3-13
Table 3-1 
HVPS - 
P45 I/O Pinout
PIN # Description PIN # Description
1 GND (+80V) 9 +15V
2 GND (+15V) 10 -15V
3 GND (-15V) 11 G1 SUPPLY
4 GND (G1) 12 /HV_ENA
5 /HV_OK 13 V PARABOLA
6 H PARABOLA 14 H DRIVE (HVPS_SYNC
7 GND (DAF)
8 +80V
Figure 3-6  
High Voltage Power Supply.
5. Carefully slide the cover upward and outward to remove it.
NOTE
: Refer to Figure 4-5 for the remainder of this procedure.
6. Disconnect the three CRT Anode Cables.
7....

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Model 250 Service Manual
10. Disconnect P45 (“Control”) at upper left of HVPS.
11. Disconnect and label the three Focus cables. The square tabs on these
cables (see Figure 3-6) may have to be lifted up. Gently pry up with a
small Flathead screwdriver.
12. Remove all the cables from the slot in the cable guide located on the left
side of the HVPS.
13. Verify that all plugs and cables are removed and out of the way so the
HVPS is free to be removed.
14. Loosen (do not remove)...