BELINEA 10 55 70, Service Manual

Page: 31 / 80

Transistor ON
(a) Base input voltage
(b) Current through transistor
(c) Current through diode
(d) Capacitor current
(e) Current through deflection yoke
(f) Voltage generated in deflection yoke
Figure 3-20 Horizontal Output Voltage/Current Waves
it prevents DC unwanted DC currents
ing through the deflection yoke which would
otherwise cause an undesirable deflection of
the CRT beam.
curve to the linear ramp, resulting in
linearity errors in the displayed image.
In addition to the AC coupling of the deflection
yoke, another
major difference is that the
Secondly, the voltage drop across it due to the
AC ramp current flowing causes a parabolic
modulation in the slope of the ramp, leading to
a progressive curve in the ramp, symmetrical
about the zero current value as shown in Figure
3-23, below. This intentional distortion of
linear ramp is required to compensate for the
‘S’, or symmetric linearity distortion in
CRT.
In series with C31 I and the deflection yoke is
another indicter,
This is a saturating in-
dictor is biased with a permanent magnet.
Consequently this device has a linearity that is
higher for current flow in one direction than in
the opposite direction. This function provides
compensation for resistive losses would
otherwise cause an undesirable exponential
damper diode is split into two diodes. A second
resonant circuit comprising of
and
are connected at this point. This second reso-
nant circuit acts
as a smaller version of
circuit. A ramp is set up in
proportional to the voltage at the output
of the modulator circuit, VDM. A small
is also across as
a of this. Conscqucntly, the voltage seen
across winding is the difference be-
tween constant main pulse
seen across Q301 and the smaller, variable
pulse seen across As the current
flowing in the yoke is proportion to this differ-
ence, the deflection current (and therefore the
displayed image width) can hence be modu-
lated by varying the diode modulator voltage,
3-20