Service manual

CA-19
Deflection Control
voltage. The HV shutdown circuit utilizes a rectified DC voltage across CX3003. This voltage is applied to
a zener diode, ZDX3004, through a voltage divider consisting of RX3013, RX3015, RX3016, and
RX3022. The actual value of the zener will vary according to screen size. When this DC voltage becomes
high enough, the zener begins to conduct. The resulting voltage can be metered at pin 29 of ICX2200. If
the voltage in the shutdown pin is above +3.5 volts, the ICs internal shutdown circuitry will trigger and
deactivate all horizontal signal from the IC, thereby shutting off the set. In this case, the microprocessor will
have to be reset before the television can be powered on.
Width and Geometry Correction
Width and east/west pincushion correction circuitry may be found on receivers with 27 - 36 inch picture
tubes. Smaller sets have pincushion correction preset in the windings of their deflection yokes. Otherwise,
width is controlled in the CA chassis digitally through the microprocessor, IC6000, using an internal pulse
width modulator. The width control signal is emitted from pin 47 of the microprocessor and is supplied to
C3250. This operation is very similar to the vertical size adjustment. The resulting DC voltage effects the
biasing of transistor Q3250, thereby changing the current in coil LX3201 and ultimately altering the width.
<<Figure CA-18>>
R3252
C3250
Q3250
R3255
Horz Size Pulse
RX3256
R3253
QX3251
R3257M
TP3200
R3259
CX3251
LX3201
DX3250DX3251
CX3252 CX3216
CX3256
C3217
H-Output from QX3203
LX3262
HYoke
+35V
RX3215
CX3215
DX3203
RX3214
CX3218
C3255
R3258
W3203
W3200
W3201
W3202
Vertical Rate
Drive
Vertical
Parabola
The pincushion correction is accomplished using diode modulation. Key components of this circuit include
the width coil, LX3201; the horizontal yoke; CX3216 and CX3252; CX3217, used for S-correction;
LX3262, for linearity; DX3250 and DX3251 as dampers; and QX3251 and CX3251, used for amplifying
the vertical parabola waveform. This circuit uses the parabolic waveform from IC2100, the vertical ampli-
fier, to shorten the horizontal scan lines on each end of the vertical trace. As the vertical trace is near its
extremes, voltage across CX3251 is increased. The result is a lower net voltage across the horizontal yoke
coil which translates to less beam deflection. Conversely, when QX3251 modulates a lower voltage across
CX3251, particularly when the vertical scan is closer to the middle of its trace, deflection is increased. The