COMPONENT MAINTENANCE MANUAL
IN 1502H RADAR INDICATOR
TM109102
1-30
May/01
half of the 700 volts appears at the center tap between C2027 and C2030. Capacitor
C2032 charges through CR2015, which peak detects the 250 to 285 volts.
The -160 volt output for the brightness circuit is obtained from the negative side of
C2032. This voltage is routed to the video board via CR2013 and R2066. The actual
negative voltage level on this line will vary, depending upon the setting of the front
panel BRT control.
The third DC voltage output (SWEEP REF) is obtained by regulating the +250 volt
output down to +27 volts through R2062, R2067 and Zener diode CR2018. The final
output (VID EN) is obtained from the +250 volts by dropping 200 volts across Zener
diode CR2014, 40 volts across R2064 and 5.1 volts (VID EN) across CR2017.
C. High Voltage Power Supply (See figure 6-5 or 6-8.)
The high voltage power supply consists of the high voltage tripler potted assembly and
high voltage regulator module, which is mounted on the potted assembly. The regulator
module includes the high voltage supply on/off circuit, a pulse width modulation control
circuit, driver and a current limiter/soft start circuit. The focus adjustment and grid 2 bias
circuit are also located on this module. The potted assembly contains a high voltage
tripler assembly and the horizontal static convergence assembly. The high voltage tripler
printed circuit board includes a high voltage flyback transformer and the voltage tripler
circuit. A small portion of the high voltage output is fed back to the high voltage regulator
module via the horizontal static convergence adjustment assembly.
(1) On/Off Circuit
When the horizontal sweep circuit is operating, the sweep reference (+27 volts) is
applied to the base of Q4001. This causes the transistor to conduct, ap12
volts to pin 12 (supply voltage input) of pulse width modulation control circuit U4001. If
the horizontal sweep circuit stops operating, the sweep reference input drops to zero
volts, shutting off Q4001 and removing power from U4001. This keeps the high
voltage supply off as long as there is no horizontal sweep.
(2) Driver
Transistor Q4002 is switched on and off, under control of pulse-width modulation
control circuit U4001, to deliver high voltage pulses via flyback transformer T4501 to
the high voltage tripler assembly. The transistor is an n-channel MOSFET capable of
continuous operation with up to 10 amperes drain current.
On the P/N 300-09684-0501high voltage power supply, an inverting high-speed power
MOSFET driver (U4002) is inserted between U4001 and the gate of Q4002. The
U4001 output is taken from the collector outputs (pins 8 and 11) while the emitters
(pins 9 and 10) are grounded. By off-loading the power driving duties to the MOSFET
driver, the power supply controller can operate at lower dissipation, improving
performance and reliability.
The document reference is online, please check the correspondence between the online documentation and the printed version.
