East-West Regulator - Zenith ZCM-1490 Service Manual

Pin 4 of IC7001 is the Y(+) multiplier input, pin 8 is
the Y(-) multiplier input, pin 9 is the X(+) multiplier
input, and pin .12 is the X(-) multiplier input. Each of
these inputs is biased and balanced by a cor-
responding resistor: R7003 for pin 4, R7010 for pin 8,
R7013 for pin 9, and R7015 for pin 12. When the in-
puts are balanced, a vertical ramp applied to both
pins 4 and 12 will produce a parabola at the output of
the multiplier.
A ramp waveform at the vertical scan rate is added to
the parabola to correct trapezoidal distortion at the
left and right sides of the raster. To add the ramp to
the parabola, the bias of the (balanced) inputs of
multipler IC7001 is offset. When the bias is offset, a
portion of one of the input signals is present at the
output of the multiplier. In this manner, the vertical
ramp is "added" to the parabolic waveform. The input
bias is offset by R7011 and R7012, the E-W trap
(trapezoid) control. R7012 adjusts the amount of off-
set to obtain the desired amplitude and polarity of the
vertical ramp to be added to the parabolic waveform.
.
.
The outputs of multiplier IC7001 are applied to the
differential amplifier formed by transistors 07007 and
07008. The output from pin 2(+) is applied to the
base of 07008. The output of 07008 is coupled to
the E-W level control (R7027) by C7007. R7027 con-
trols the amplitude of the parabolic waveform. The
signal from the E-W level control is coupled to the E-
W regulator.
The multiplier output from pin 14(-) is applied to the
base of 07007. The output of 07007 (a parabolic
waveform) is integrated by C7010 to form a sine
wave. This is the sine wave mentioned earlier that is
added to the parabolic waveform to correct phase
errors. The sine wave is buffered by 07009 and ap-
plied to the E-W phase control (R7039). The signal
from the E-W phase control is applied to the E-W
regulator.
The E-W waveform generator must also produce the
proper correction waveform regardless of changes in
horizontal and. vertical display sizes. A vertical size
change is automatically compensated for because
the vertical ramp amplitude determines the vertical
display size. Thus, a larger ramp at the input of the
multiplier circuit results in a correspondingly larger
output. To compensate for a change in the horizontal
Circuit Descriptions
display size, the B+ voltage supplied to the horizontal
deflection circuitry is sampled and used to adjust the
correction waveform accordingly.
The B+ voltage at pin 2 of connector 8V6 is scaled
and filtered by R7037, R7001, and C7002. Transistor
07001 compares the resulting signal to a fixed volt-
age of about 12V (sensed by R7004). The output of
this transistor is applied to the K (multiplication con-
stant) input (pin 3) of IC7001.
As
the sampled B+
voltage changes at the base of 07001, the current
applied to the K input of IC7001 changes. Because
the output of the multiplier circuit is KXY (a constant
times the X and Y inputs), the K factor corrects the
resulting parabolic waveform as the horizontal size
changes. In this manner, changes in either the
horizontal or vertical size are compensated for.
East-West Regulator
The E-W regulator determines how much of the E-W
correction waveform is imposed onto the horizontal
scan voltage. It also supplies the current (with the
correction waveform) to the horizontal deflection cir-
cuitry. Refer to Figure 5-6.
~---~~
...... '.,3
Figure 5-6. E-W Regulator
.........
f-----r-- ......
PIN 2
eno'"
4.71100v
J
The output of the E-W level control (R7027) is cou-
pled to the non-inverting input of IC7101 by C7008
and R7028. R7027 controls the amplitude of the
parabOlic waveform that is applied to IC7101.
The output of the E-W phase control (R7039) is ap-
plied to both the inverting and non-inverting inputs of
IC7101. When this control is set to its midpoint, the
sine wave formed by integrating the parabola signal
at C7010 is applied equally to both inputs. Thus, no
part of the sine wave appears at the output of
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