Hughes JVC 220, Service Manual

Page: 24 / 140

Chapter 2---System Description
/COVER_ON: Cover interlock signal. Indicates both covers are in
place.
/LAMP_OK: Tells the ALPS that the lamp is installed, the
temperature is within limits, and the lamp cooling blower is
working.
Outputs:
+140 VDC boost voltage to the Laser Power Supply.
Voltage: 18 to 25 VDC to maintain the arc lamp ON.
Current: 45 to 50 amps to maintain the arc lamp ON.
LAMP_OUT: Lamp output voltage, positive.
LAMP_RTN: Lamp return.
/LAMP_LIT: Signal to SCB that the lamp is lit.
Operation:
Two signals (/COVER_ON and /LAMP_OK) are required in order
for the arc lamp to light. /COVER_ON from the cover interlock
switches tells the Arc Lamp Power Supply that the covers are in
place and the interlock switches are pressed down. /LAMP_OK
informs the System Controller that the lamp is installed (a
mechanical switch activates when the lamp is installed) The
System Controller then sends the /LAMP_ENA signal to the ALPS.
The /LAMP_ENA signal turns on the ALPS.
The Arc Lamp Power Supply then provides the +140 VDC boost
voltage to a spark gap and high voltage transformer which steps
up the voltage to approximately 32KV and ignites the Xenon Arc
Lamp. After the Arc Lamp is lit, it is maintained on by the ALPS at
a steady 20 volts and 47.5 amps. The /LAMP_LIT signal output
informs the System Controller if the lamp is lit or not.
The Arc Lamp Power Supply is electrically and magnetically
shielded to prevent noise or disturbances in the CRTs or other
circuitry.
High Voltage Power Supply (HVPS)
The High Voltage Power Supply (HVPS) is located on top of the
LVPS on the right side of projector ( as viewed from rear). This
supply provides the anode, focus, and screen voltages required
for the three CRTs in the Model 220 projector.
The following functions are provided by HVPS:
•
Phase locked loop circuit for synchronization to the horizontal
sync
2-10 Model 220 Service Manual