Onkyo TX-7230 - Auto Search Tuning Circuit; FM;AM Switch Circuit

TX-7230
3. Auto search tuning circuit
Q103
FM IF
SYSTEM
TO
STEREO
DECODER
D811
Ww WwW
0702
CONTROLLER
Q806
NOISE
DETECTOR
From
AM IC
To :
Signal
indicator
circuit
Maximum frequency
Station B
Station A
Start
Minimum frequenc
= a (fig. 4)
4. FM/AM switch circuit
+B Q702
Q155
Q709 (ON
The FM/AM selector circuit is shown in the diagram. fig.5.
Pins 4 and 5 of Q702 are of the mutual reset type. For FM,
pin 4 is high and pin 5 is low; for AM, pin 4 is low and pin
5 is high. Because pin 5 is high and pin 4 is low during AM
reception, Q709 is off, the AM, kHz segments of the fluores-
cent display are turned on. Also, since Q708 goes to on and
Q714 is turned off, and the FM indicators are turned off.
At the same time, Q155 is turned off and Q154 turned on,
so
+B
is
supplied
to
the
power
source
terminal
of
the
radio
Q154
To AM/kHz segment
To FM/MHz segment
During FM reception, this is operated by the IF level detec-
tion and zero point detection circuits included in the FM IF
system IC of Q103 and by the noise component detection
circuit
of
Q806.
When
a
station
is
tuned,
the
output
of
all
outputs
go
to
the
low
level
so
Q843
goes
from
on
to
off,
causing
pins
32
and
33
of
the
controller
IC
to
go
to
the
high level to complete auto search tuning.
During AM reception, this is operated by the IF level detec-
tion included in the AM radio system IC of Q151. When a
station is turned, Q152 goes from off to on and Q706 goes
to off, causing pins 32 and 33 of the controller IC to go to
the high level to complete auto search tuning.
@ Manual Tuning
When the UP or DOWN key is pressed, the frequency
goes up or down by one step. When either key is held
down, the frequency rapidly increases or decreases
(scans) and stops when the key is released. When either
end of the turning range is reached, key input will no
longer be received and the frequency will stop at the
highest or lowest frequency.
e@ Auto Tuning
When the UP or DOWN key is pressed, scanning begins
in the up or down direction, stopping where there is a
radio station. Since auto scan is operated by a trian-
gular
wave,
scanning
is
begun
in
the
opposite
direction
the instant either end of the tuning range is roached.
Also, if the UP or DOWN key is pressed when the tuned
frequency is not at either end of the range, up or down
scanning will begin.
Pin 16 of Q201
VCO stop terminal
of stereo decoder
Pin 2 of Q103
FM IF Amp,
stop inpu
Muting circuit
——— -
D119
Q108
Pins 8 & 14
AM B+ Terminals
( ): FM reception
from A. G. C detector circuit
(fig. 5}
system pins 8 & 14 of QIS].
Pin
16
of
Q201
goes
to
the
high
level,
the
VCO
oscillator
stops,
and
pin
2
of
Q103
gose
to
the
high
level
so
the
FM
IF
amp
is
also
switched
off.
Also,
during
AM
reception,
Q108
is
turned
on
so
the
muting
circuit
is
off.
During
FM
reception,
all
of
the
switching
transistors
mentioned
above
perform
the
opposite
operations
to
switch
to
the
FM
mode.
Figures
in
parenthese
indicate
transistor
Operation
during
FM
reception.
—10—