Sony TC-161SD - Page 5

1-2.
SYSTEM
CONTROL
“CIRCUIT
DESCRIPTION
(Refer
to
schematic
diagram
on
page
6.)
The TC-161SD uses two automatic stop mechanisms;
1.
In
playback,
record,
rewind
or
fast
forward
mode,
SONY
Magnetodiode
«
detects
reel
spindle
stop
at
tape
end and
operates
tape
stop
mechanism.
2. In rewind mode, switch built in tape index counter
operates tape stop mechanism, at O00 counter
reading.
*: The diode developed’ by SONY is extremely
sensitive to magnetic field.
Automatic Stop Function at Tape End
In playback, record, rewind or fast forward mode:
|. Ferrite magnet ring belt-driven by supply reel
spindle rotates.
2. Magnetodiode D401 detects magnetic field varia-
tion produced by ferrite magnet ring rotation as
an AC signal.
3, The AC signal is amplified by transistors Q401 and
Q402, and rectified by diodes D402 and D403.
4. Rectified DC voltage charges C405 and charging
current flows through C405 and R413 since the
rectified DC voltage is higher than B + voltage
divided by R412 and R413,
5. Rectified DC voltage turns 0404 ON and decreased
collector voltage of Q404 turns Q405 and Q406
OFF.
6. Solenoid PM | remains de-energized.
At tape end:
1. Ferrite magnet ring stops.
2. D401 detects magnetic field variation stop.
3. Due to no AC signal input to Q401, current flow
to D403 stops. a
4. C405 discharges through R419, Q404 emitter and
R429.
5. After the discharge, Q404 turns OFF and conducts
Q405 and Q406.
Note: In playback, record, rewind or fast for-
ward mode, $3-4, S13 or $14 yvround DC
bias supply circuit used for Q404 base.
6. Solenoid PM | is energized and stops tape transport
mechanism.
Starting:
1.
In
stop
mode,
DC
bias
is
applied
to
Q404
base
through
R417,
R418
and
R419
and
Q404
turns
ON.
,
2.
With
forward,
rewind
or
fast
forward
button
de-
pressed,
ferrite
magnet
ring
starts
to
rotate
and
turns
Q404
ON
before
$3-4,
$13
or
S14
ground
DC
bias
supply
circuit
used
for
Q404
base.
3. Solenoid PM | remains de-energized.
Manual Stop Function
1.
With
STOP
button
depressed,
S11
closes.
Voltage
across
C405
increases
and
charging
current
flows
through
C405.
2.
This
charging
current
decreases
Q404
base
voltage.
3.
Q404
turns
OFF,
solenoid
PM
1!
is
energized
and
stops tape transport mechanism. -
Manual.Pause Function
1.
With
PAUSE
button
depressed,
S12
closes
and
supplies
bias
voltage
to
Q404
base
through
R414
and
R419.
bo
energized.
Memory
Counter
Stop
Function
In
rewind
mode,
tape
transport
automatically
stops
when
tape
index
counter‘indicates
000.
This
function
is
useful
for
repeated
playback
of
desired
tape
por-
tion.
;
1.
When
tape
counter
indicates
000,
$16
closes
and
turns
Q403
ON
during
charging
of
C407.
Then
Q404
base
bias
is
grounded
through
Q403,
S15
and
S14
Solenoid
PM
1
is
energized.
. D405 operates the memory counter system only
in rewind mode.
Muting Circuit
in)
When STOP button is depressed, muting circuit elimi-
nates click noises as follows:
I. STOP switch ($11) closes and turns Q404 OFF.
2. Increased collector voltage of Q404 turns Q302
ON.
3. Q301 turns OFF.
4. Q301 collector voltage becomes higher than zener
voltage of D301 and turns Q107 and Q207 ON.
5. Q107 and Q207 ground audio signal circuits, thus
click noises are eliminated.
.
Q404
turns
ON
and
solenoid
PM
1
remains
de-