Philips PM 5390 Service Manual page 14

3-5
3.3.
MODULATION INTERFACE, UNIT
3,
fig-
39
Processing and matching of the
modulation
signals
for the
RF
units,
i.e.
the
internal
and
external
am
or
VIDEO
are
achieved
by
unit 3.
The
different
modes
are
controlled via
ports P1/B0-6, P1/A4-7,
P1/A0-1 of
CPU,
unit
1,
and
are
switched
by
inverters
351/352 and FET-switches
353
...
356.
These
switches
are
supplied
by
~2
V
at
pin 7
and +12
V
at pin 14.
Detailed
information of the logic states
and port outputs for
all
modulation
modes
is
given
in
table
fig.1
IC318
(U1)
PORT1
/
BO
...
6
PORT1
/
AO... 7
6 5
4 3
2
1
0
7
6 5
4
3 2
1
0
Pin
U1
B11
BIO B9 B8 B7 B6 B5
B14 B13 B12 C26 C25 C24 C23 C22
Pin
U3
5
6
7
8 9 10
11
2 3
4
1
12 not used
ident.
U3
E F
G
1
K
B
B
C D
A
H
-
-
AM
int 1 1 1
1 1
0 0
1
0
1 1
1
1
AM
ext
1 1
0
1
1
0
1 1
1
1
1 1
FM
int
1 1 1 1 1 1
0
1
1
1
0
1
FM
ext
1 1 1
0
1
1 1 1 1 1 1 1
VIDEO
1 1 1 1
0
1
1 1 1 1 1
1
VFM
int 0
1 1
1
0
1
0
1
1
0
1
0
V.FM
ext
0 0
1
1
0
1 1 1 1 1
1
0
VAM
int
1 1 1 1
0
1
0 0
1
0
1
0
VAM
ext
1
0
1 1
0
1 1
0
1 1
1
0
,
Fig.
1
Unit
1
and
3; logic states
of port
outputs for
modulation
modes
The
sound part consists of
a
sound
carrier
oscillator/modulator (switched
in
during
VIDEO),
a
1
kHz
oscillator
and an input
circuitry for external/internal
sound
signals
for generation of
AM
and
FM
modu-
lation.
The
1
kHz
oscillator
is
a
RC
oscillator
based
on the Wien-bridge
principle,
the
components
of
which are
654,
535, 534, 659.
A
rectifier
is
added balancing the differential
amplifier
307/1.2.
So
the stability
of oscillation
and amplitude
is
achieved.
The
oscillator
is
switched
in
by 355/L.
For external
FM
sound
signals a
decoupling preamplifier
306, 307/5,
308
is
available.
By means of
soldering link
F the required pre-emphasis of
50
jus
can be obtained.
In
VIDEO/FM-mode
the
modulation
signal
is
applied
via
FET-switch
355/E to the
sound
carrier
osciHa-
tor/modulator. In
FM-mode
(f
=0.1
- <
340 MHz)
the
FM
modulation
signal
is
applied
via
switches
354/H
or
356/A and output
FM
(point 21
)
directly to
the RF-unit
1
.
In
VIDEO/AM-mode
the
modulation
signal
is
applied to the
sound
carrier
oscillator/modulator via
FET-switch 355/B.
In
mode RF
carrier
/
AM
the
modulation
signal
is
fed
via
IC
357
to the
AM
am-
plifier
304/4
...
1
1.