GE 4PE350A3 Instructions Manual page 35

COLOR CAMERA
to yoke resistance. A sample of the sweep
is applied to the base of Q19. The signal is
then coupled to transformer T3 by Q19. The
output of T3 drives a push-pull stage con-
sisting of Q17 and Q18, whose output feeds
transformer T2. The secondary of T2 is,
in effect, in series with a main sweep cur-
rent; therefore, the correction current is fed
in series with the main sweep current. Po-
tentiometer R67 is used to adjust the lin-
earity of the sweep. The width is controlled
by the WIDTH potentiometer on the registra-
tion control panel, which governs the d -c
voltage on Q16.
CAMERA BLANKING CIRCUIT
A circuit is provided to produce Camera
blanking and sweep failure protection. This
circuit is so arranged that if either sweep is
missing, the Plumbicon tube is turned off
to prevent damage. The blanking voltage is
applied to the cathode of the Plumbicon tubes;
therefore, a positive voltage cuts off the tube
and, conversely, a negative voltage turns it on.
Q9 and Q12 have a common collector load.
Therefore, whatever signal is present on
either base appears on the common collector.
Without a signal to either base, the col-
lectors are at +40 volts because both tran-
sistors are in saturation. Since this plus,
or positive, voltage is d -c coupled by Q10
to the cathode of the Plumbicon, the tube is
turned off.
As long as both sweeps are present, the
collectors operate between cutoff and sat-
uration, which turns on the tube during the
active part of blanking and turns it off during
the blanked -off time. If either the horizontal
or vertical sweep is missing, its correspond-
ing transistor is in saturation and the col-
lector voltage is at +40 volts.
Q8 is used to shape the vertical portion of
blanking, and Q13 is used for the horizontal
portion.
Q23 is a voltage regulator used to obtain
+40 volts from +100 volts.
FOCUS REGULATOR CIRCUITS
A focus current regulator is provided to
compensate for current changes due to re-
sistance changes in the focus yokes.
EBI-6351
Q20 is a dual transistor which is used as
a differential amplifier. The voltage on one
base is fixed by a divider, R76 and R77,
one percent resistors. The voltage on the
other base of Q20 is fixed by the voltage
drop across R74. This resistor is in series
with the focus current; therefore, the base
voltage is proportional to this current. Any
change in focus current unbalances the dif-
ferential amplifier, and the voltage at the
base of Q21 changes. Q22 is a series regu-
lator, so that a change in base voltage causes
a change in focus current. The circuit is so
arranged that when focus current changes
occur, the voltage applied to the base of the
series regulator is in the direction to cor-
rect the original change.
Skew Generator Board, PL -7781890
Refer
to
the Waveforms, Fig. 37, the
Printed Circuit Diagram, Fig. 38, and the
Schematic Diagram, Fig. 39.
The input signal to the skew generator is
a vertical rate sawtooth with an amplitude
of 1.5 volts, peak -to -peak, derived from the
Camera sweep board. The input stage of the
generator, Qi, is
a unity gain device that
provides an inverted and noninverted form
of this input. These inputs are routed along
two bus lines that have four potentiometers,
R5, R7, R9, and R11, connected across them.
The potentiometers are used to select the
amount and polarity of the correction needed.
Following each potentiometer control is an
emitter -follower buffer, which serves as an
output stage. The skew voltage is de -coupled
through the chokes to prevent horizontal
sweep from entering the system.
The maximum output of the positive or
negative polarity is 1.2 volts, peak -to -peak.
Camera Power Supply Board,
PL -7674504G2
Refer to the Waveforms, Figs. 40 and 41,
the Printed Circuit Diagram, Fig. 42, and
the Schematic Diagram, Fig. 43.
The d -c to d -c converter power supply
portion of this board operates from a +100
volt source controlled by a series regulator
21