Service manual

CB-26
CB CIRCUIT DESCRIPTIONS
Width and Geometry Correction
East/West pincushion correction is performed by circuitry built into 32 and 36 sets. The windings of the
yokes used in the 27 CB chassis have this correction shaped into their design at assembly. Correction is
necessary on larger sets due to their geometry. As the CRT electron beam approaches the upper and lower
extremes of the screen, its horizontal scan lines sweep a wider length than they do in the middle of the
screen. DX3250, DX3251, CX3216, CX3252 and CX3256 act as a diode modulator circuit to limit
current in the horizontal yoke when the sweep is at the higher and lower edges of the screen. This diode
modulator relies on signals amplified by Q3250 and QX3251, and supplied by both the vertical yoke and
the video processor. Q3250 receives its power from the +35V derived at CX3253 off the flyback.
IC3200 is an op-amp that boosts the signal from IC2200. It is powered by the +15VSW, and provides
not only pin-correction information, but also width control. Varying the DC level on the base of Q3250
alters the overall screen width by changing the current through LX3201, the width coil.
R3252M
Q3250
R3255M
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
+15VSW
R3251M
W3259
W3202
LX3203
W3200
W3203
1 2 3 45
6 7 8
IC3200
C3224
R3268
R3267
E/W
R3266M
ABL
+15VSW
R3261M
R3262M
R3263M
R3264M
Vertical
Parabola
<<Figure CB-26>>