HP 8414A Operating And Service Manual page 102

Section VIII
Service
SCHEMATIC 4. CIRCUIT DESCRIPTION
CRT, CRT POWER SUPPLIES
+150V Power Supply.
The +150V power supply is
a regulated supply. Reference Amplifier, A3Q2
senses a change in output voltage, amplifies that
change and inverts the polarity of the change. The
output of the reference amplifier changes the con¬
duction of Driver A3Q1, which changes the con¬
duction of Series Regulator A3Q3. The series regu¬
lator acts as a variable resistor whose resistance
varies inversely with collector current; i.e., if the
series regulator's base voltage goes in a negative
direction, its collector current decreases, dropping
more voltage across the regulator, decreasing out¬
put voltage.
High Voltage Oscillator.
High Voltage Oscillator
Ql, Q2 is a free-running multivibrator whose
frequency, 20 kHz ±2 kHz, is determined by the L
and C of Tl's primary.
CRT Cathode Supply.
One of Tl's secondary
windings supplies power to the CRT's cathode
A_
f A3TP2 50 mV P-P
supply and anode supply. The cathode supply
consists of a half-wave rectifier and pi section
filter. Its output voltage is about -2450 Vdc. In
addition to providing dc bias to the CRT cathode,
the cathode supply's output voltage is used in a
voltage divider to +150V to provide about -2000
Vdc to the front-panel focus control.
CRT Anode Supply.
The anode supply consists of
a voltage doubler and pi section filter. Its output
voltage is about +5100 Vdc.
CRT Grid Supply.
The grid supply consists of a
half-wave rectifier or peak detector. Its output
voltage is about -2500 Vdc with the CRT un¬
blanked. With no input from the intensity modula¬
tor, the grid supply is referenced to ground; how¬
ever, an input voltage from the intensity modulator
becomes the reference voltage for the grid supply.
A change in this input voltage causes the grid
supply's output voltage to change, which changes
the CRT's grid to cathode bias.
B
Ql COLLECTOR 40V P-P
8-18