BELINEA 10 55 70, Service Manual

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tor output, is added to horizontal B+ to provide
pincushion distortion correction.
diode modulator pm-amplifier provides
this filtering action. The op amp is con-
figured with 4353 to provide a current source
output at the collector of 4353 . The
parabola is filtered to remove horizontal rate
harmonics by 657.
3.2.4. Structure of Horizontal Deflection Circuit
The function of the horizontal deflection circuit is to
cause left/right scanning of the electron beam using
the sawtooth wave current flowing through the hori-
zontal deflection yoke, and is made up of the hori-
zontal oscillator circuit, horizontal drive circuit,
horizontal output circuit. synchronous AFC circuit
and high voltage generator circuit.
1.
Horizontal Drive Amplifier
In order to rapidly saturate the output transistor
(ON) or cut it off (OFF), a sufficient basic
current must be provided. Because of this, an
amplifier circuit is added between the oscillator
circuit and the output circuit to amplify the
pulse voltage. At the same time, after the wave-
form has been regulated, by adding this circuit
to the output circuit, this amplification circuit
functions as a drive amplifier.
2 .
The sawtooth wave is from Pin of
and C354 and and input
to Pin 2 of It is then output Pin 1
of and after being sent to collec-
2 .
IC UPC1883 consists of a vertical sawtooth
wave generator, horizontal sawtooth wave gen-
erator, horizontal oscillator circuit, vertical os-
cillator circuit, AFC circuit, phase regulator
circuit, geometry control circuit and drive am-
plification circuit. This
includes the vertical
and horizontal circuits combined in one pack-
age.
When the synchronization signal input to Logic
circuit and pin 26 of
The pin 18 of
output horizontal frequency is achieved
by the pin 12 and pin 13 of (D.A.C
control) and pulse pin 6 of
fed to pin 17 of so the pin 18 of
output horizontal frequency through
4374, Q3 and provide a hori-
zontal output transistor base current of 1.
The horizontal output transistor base drive
is
taken from a conventional base trans-
former stage. This circuit
as in a similar
to
a
power supply. The square
horizontal oscillator output signal is coupled
into the base of base drive stage transistor,
via C334, D333, R326,
Q3 turns on and connects the primary wind-
ing of transformer across the and
supplies. This causes the primary current
to increase linearly until such time as 4310
turns off, hence storing a predetermined
amount of flux energy in the transformer. As
10 tums off, and the primary current falls to
zero, the secondary voltage is driven above the
threshold of the base-emitter junction voltage
of the horizontal output transistor, 4301. Cur-
rent flows through R457, R329 and
D3 12 into the base of 4301 hence turning this
device on. The high base current of around
Lamps
is
so high 4301 is driven
heavily into saturation. This is important in
order that the collector voltage should be as low
as low as possible whilst conducting the high
peak currents that flow through the horizontal
deflection winding. In turn. this is vital to limit
dissipation.
At the required time as determined by the hori-
zontal oscillator, the base drive transistor is
turned back on. The voltage at 4310 collector
fall rapidly back towards the rail. How-
ever, the secondary current still remains flow-
ing in a positive direction for a short time, due
to the finite leakage inductance of
Also,
due to the heavy saturation of the base
voltage remains at around The current in
the secondary winding rapidly reverses and
goes sharply negative as the charge stored
within the base region of
is removed
Diode D312 helps to speed up this charge re-
moval. Note that during this time, the collector
output of the
is still turned on, even
though the base current is flowing out of the
base.
This period of time is known as the storage time
of the device and may take between
depending upon peak collector current and
temperature and various other design factors.
Finally, when all charge in the base region of
is dissipated the base current suddenly
stops, and the secondary current drops almost
instantly to
zero. At
that point, the device now
become non conducting and the collector cur-
rent flow also terminates. The secondary volt-
age on
drops to it’s unloaded voltage and
the current flow in the primary settles to it
initial value once more.
3.
Horizontal Output Circuit
The horizontal output circuit uses the switch
operation of a transistor and a damping diode,
and
a sawtooth wave current to the
dcllection horizontal deflection yoke
is made up of L on coil and
the coil connected in series.
Its resistance is extremely small, and the time
constant
is
extremely Because
of
this
the voltage at
the
two
terminals of
the coil
cause rapid variation in the current flowing in
the coil still will slowly vary, creating a