and horizontal positions of the electron beam.
Therefore, overall focus is improved over the crt
display area. Figure 4-3 illustrates the typical
correction-voltage curve as the beam is deflected over
the crt display area. The correction-voltage curves for
vertical and horizontal deflection are not identical;
however, the theory is the same.
I
I
I
I
:
.....-- CRT DISP LAY A R E A
:
CRT
CENTE R
I
- - +80 V
1
- - - - - - - +20 V
VOLTAG E
D E F L ECTI O N
2025· 1 8
Figure
4- 3 .
Typical correction-voltage curve applied t o the
crt focus element (correction voltage applied for both
vertical and horizontal deflec�ion).
X FOCU S - C O R R ECTION SHA P E R
Samples o f the +X and
- x
horizontal signals, from the
X Focus-Correction Pickoff stage shown on diagram 2,
are coupled to the X Focus-Correction Shaper stage of
the Dynamic Focus circuit. Quiescently, with the crt
beam horizontally deflected within about 3 divisions of
center screen, Q710-Q720 are conducting and CR710-
CR720 are reverse biased. The voltage level at the
anodes of CR710 and CR720 is approximately +5.1
volts, as determined by zener diode VR750 and
transistor Q750.
As the beam is deflected to the right side of the crt
display area, the output of Q710 falls below +4.5
volts, forward biasing CR710 (CR720 is reverse
biased). The signal is coupled through R715 (Right)
and applied to the Summing and O utpu t Amplifier at
the emitter of Q750.
As the beam is deflected to the left side of the crt
display area, the output of Q720 falls below +4.5
volts, forward biasing CR720 (CR710 is reverse
biased). The signal is coupled through R725 (Left) and
a pplied to the Summing and O u tput Amplifier at the
emitter of 0750.
Y FOCU S - C O R R ECTI ON SHA P E R
Samples o f the
+Y
and
- Y
vertical signals, from the
Y
Focus:Correction Pickoff stage shown on diagram 1,
are coupled to the
Y
Focus-Correction Shaper stage of
the Dynamic Focus circuit. Quiescently, with the crt
beam vertically deflected within abou t 3 divisions of
@
Theory o f O peration-SOS
center screen, 0730-0740 are conducting and CR730-
CR740 are reverse biased. The voltage level at the
a nodes of CR 730 and CR740 is approximately +5 . 1
volts, as determined by zener diode VR 750 and
tra nsistor 0750.
As the beam is deflected to the bottom region of the
crt display area, the output of 0730 falls below +4. 5
volts, forward biasing CR730 (CR740 is reverse
biased). The signal is coupled through R735 (Bottom)
and applied to the Summing and Output Amplifier at
the emitter of 0750.
As the beam is deflected to the top region of the crt
display area, the output of 0740 falls below +4. 5
volts, forward biasing C R740 (CR730 is reverse
biased). The signal is coupled through R745 (Top) and
applied to the Summing and Output Amplifier at the
emitter of 0750.
S U M M I N G AN D O UTPUT AMPLI F I E R
Outputs from both the X and
Y
Focus-Correction
Shapers are added in the Summing and Output
Amplifier stage. The focus-correction signals are
coupled to common-base transistor 0750. Diode
CR753 limits the output of 0750 to prevent
overdriving the Output Amplifier. The Output Amplifier
of this stage, consisting of transistors 07S0-0765-
0770-Q776, is an inverting operation amplifier. The
input signal to this amplifier is developed across R 753.
The feedback network for the Output Amplifier
consists of R7S9 and C7S9-C7SS. Emitter followers
0760 and Q765 provide current amplification for
0770 and 0776, which are connected in a collector
coupled complementary amplifier configuration. The
composite correction signal is coupled to the Focus
Element DC Restorer stage of the High-Voltage Power
Supply circuit (diagram 5).
H I G H -V O LTAG E POW E R S U PP LY
<$>
The High-Voltage Power Supply provides the voltage
levels and control circuits necessary for operation of
the cathode-ray tube (crt). A schematic diagram of the
High-Voltage Power Supply is shown on diagram 5. A
detailed block diagram, showing each major stage of
this circuit, is superimposed on the schematic diagram
with wide shaded lines. The stage names (given as
sub-headings in the following discussion) can be found
in the shaded boxes on diagram 5.
H I GH -V O LTAG E O S C I LLATOR
A repetitive, sinusoidal signal is produced by a
regenerative feedback oscillator in the primary of T850
and induced into the secondary. Current drive for the
primary winding is furnished by OS1 6-0818-081 0-
OS14. The conduction of the High-Voltage Oscillator
transistors is controlled by the output voltage of the
Error Amplifier.
4-5
