Philips PM3208 - 4 Circuit Description; 4.1 Vertical Deflection

4 CIRCUIT DESCRIPTION 4-1
4 CIRCUIT DESCRIPTION
4.1 VERTICAL DEFLECTION
4.1.1 Attenuator
Ch. A and Ch. B are identical. For this reason, only Ch. A will be described. The input
signal is fed to the attenuator by means of the input coupling switch $1.
- In position "AC", the input signal is coupled via C2 to block DC components.
- In position "GND", the attenuator input is connected to ground.
- In position "DC", the input is directly connected to the attenuator.
The attenuator consists of two sections. The first one, consisting of S2a and S2b,
performs
1:1,
10:1
and
100:1
attenuation.
The
second
one,
S2c,
performs
2:1,
5:1
and
10:1.
Output
from
the
attenuator,
a
single-ended
(asymmetrical)
signal,
is
fed
to
the
preamplifier.
4.1.2 Preamplifier
Ch.
A
and
Ch.
B
are
identical.
In
the
preamplifier,
the
single-ended
output
signal
from
the
attenuator
is
converted
into
a
differential
signal
by
means
of
IC2.
In
the
preamplifier,
compensations
and
adjustments
to
obtain
a
good
signal waveform
are made.
4.1.3 Intermediate amplifier
Ch.
A
and
Ch.
B
are
practically
identical.
The
only
difference
is
the
additional
invert
facility
for
Ch.
B.
The
output
signals
from
the
vertical
preamplifier
are
fed
to
the
intermediate
amplifier
where
they
are
amplified
in
Q5-Q6
and
Q7-Q8.
(Q105-Q106
and
Q107-Q108
in
Ch.
B).
The
intermediate
amplifier
contains
the
controls
for
vertical
shift,
RV54
and
RV154,
as
well
as
the
invert
switch
for
Ch.
B.
The
output
signals
from
the
intermediate
amplifier
are
fed
to
the
driver
Q201-Q202,
under
control
by
the
vertical
switching
circuit.
4.1.4 Y-out amplifier =
For
external
purposes,
the
vertical
signal
from
Ch.
A
is
also
fed
to
the
Y-out
amplifier
Q11
and
from
there
to
a
BNC
connector
at
the
rear
side
of
the
oscilloscope.
Input
signal
for
the
Y-out
amplifier
is
taken
from
the
first
stage
in
the
vertical
amplifier
Q5-Q6
and
fed
to
Q11
via
the trigger
amplifier
Q9-Q10.
4.1.5 Vertical switching circuit
This
circuit
consists
of
the
logic
circuitry,
defining
the
vertical
mode.
Part
of
this
circuit
is
the
chopping
generator,
consisting
of
1C201.
In
position
"DUAL",
Ch.
A
and
Ch.
B
are
displayed
alternately
at
high
time-base
speeds
and
chopped
at
low
speeds.
The
output
from
the
switching
circuit
defines
whether
Ch.
A
or
Ch.
B
is
fed
to
the
driver
Q201-Q202
Control
takes
place
via
the
diodes
D60...63
and
D160...163
by
means
of
the
flip-flop
IC202
pins
8
and
9.
4.1 VERTICAL DEFLECTION