Philips PM 3266 - Page 99

104
INPUT
SWITCHING
OF
STORAGE
AMPLIFIERS
This block
produces
the output
signals
that
feed the inputs
of the
storage
amplifiers. In
turn,
these
amplifiers
drive the storage
electrodes
of the c.r.t.
The output
signals
of the INPUT
SWITCHING
block
are derived from
the output
signals,
produced
by the
DUAL
OSCILLATOR,
the ETB/BTB
PULSE GENERATOR
and the
STABILISATION
PULSE
GENERATOR.
The pulse
sequence of
the output
signals
is
determined by
the setting
of the
storage
control
pushbuttons
(S24A,
S24B,
S24C)together
with
the output
pulses from
the TIMER.
These
output
pulses
from
the TIMER
are
initiated
on the
release of
the ERASE
pushbutton
or
by the AUTO-ERASE
TIMER.
3. 1.5.8. Focus
and Z-
Amplifier
Block Diagram
Description
The
focusing
of the
electron
beam of
the c.r.t.
is
controlled
by the setting
of
the INTENSity
control (R14).
This
coupling
between
the Z-amplifier
and the
focus
is such that the spot
on the
c.r.t.
screen
remains
well
focused
over
almost
the entire
intensity
range.
The
c.r.t. has
a scan
magnifier
facility
and
this
necessitates
two focussing
electrodes;
one is
active in the
vertical
direction
and
the other
is
active in
the horizontal
direction.
The intensisty
is
influenced
by the
following
signals:
—
the setting
of the
INTENS
control (R14),
—
a signal
applied
to
the
external
Z-modulation
input X8,
—
a signal from
the
chopper
oscillator,
used
for blanking in the
CHOPped
mode,
—
a signal from
the
X-deflection
selector,
used
for
display blanking
in the ALTernate
mode,
—
a signal
that
increases
the intensity
in the TB
MAGN
xIO mode,
—
a signal from
the storage
logic
that
increases
the intensity
in
the FAST
mode,
—
a signal
from
the
AUTO,
TRIG,
SINGLE
switch
that
controls the intensity
in
the single
shot
mode.
The
above-mentioned
input signals
are
applied
to the INTENSITY
AND
FOCUS
PREAMPLIFIER.
This
amplifier
has
two
outputs
that have
identical
signals,
but with
a phase
difference
of 180
degrees.
One output
feeds the
Z-amplifier. The
other
output feeds
the FOCUS
AMPLIFIER
via a correction
network
comprising
a zener diode
and a resistor. This
network
compensates
for
the difference in
focus
and intensity
characteristics
of the c.r.t
The
output
signal from
the Z-amplifier
must
be applied
to the Wehnelt cylinder
(G1) of the c.r.t. which
stands
at
a potential of about
—3
kV.
The
h.f.
components
can be directly applied
to
G1 via a d.c.
blocking
capacitor.
However,
the d.c. and
l.f.
components are first
applied to the MODULATOR
where
they
modulate
an
h.f.
carrier. They
are
then
fed
via a d.c. blocking
capacitor to tlie DEMODULATOR.
The
output
signal from
the
DEMODULATOR
consists of the
d.c. and
l.f. components, which are
then
applied to the
Wehniet
cylinder
(G1) of the c.r.t.
The
output signal from
the FOCUS
AMPLIFIER
is divided into
two parts; one for vertical
focusing
and the
other for
horizontal
focusing.
The vertical
focusing
is controlled
by R19, which
adjusts the VERTICAL
FOCUS AMPLIFIER
that drives the
vertical focusing
electrode G5 of
the c.r.t
The horizontal
focusing is
controlled by R1 7 on the front
panel, which adjusts
the HORIZONTAL
FOCUS
AMPLIFIER that
drives
the
horizontal
focusing electrode G3 of the
c.r.t.
The deflection coefficients
of the c.r.t. are
affected by the cathode potential of
the c.r.t.
Therefore, the
—3
kV
cathode voltage is stabilised by a
—3
kV
STABILISER that has
a potentiometer adjustment
control.
3.1.6.
Stabilized
power supply
The
mains voltage
is full-wave
rectified
and fed to
a
regulated
sine converter.
The
output voltage
of the
sine converter
is kept constant
by regulating the
duty cycle
of the applied
voltage.
This output voltage
is applied to the primary of
a
transformer,
the secondary
voltages
of this
transformer
are
full-wave rectified,
smoothed and applied to the
various circuits.
The
MAINS
triggering
signal is taken
direct from the
mains and, via
an
opto-isolator, fed
to the trigger
circuitry
on
a
safe level.
An
additional
power
supply unit
makes the
supply voltages for
parts
of
the storage
system.