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switch (S8), resulting in IC1 pin 33 (and IC6 pin
2) being switched to L level), thereby stopping
the geared motor.
The tonearm thus completes
the lowering
movement
and resumes
play of
the record.
If the
elevation
button
is pressed while
the tonearm
is being lifted or lowered, the
tonearm
will immediately
start to move
in
the opposite direction.
(et)
Auto Return Operation
. When
the
tonearm
approaches
the
lead-out
groove during record play, the end sensor (LED
D53
and
photo-sensitive
transistor
Q53)
will
start to apply H/L pulse signals to pin 39 of IC1.
. When
the
stylus
finally
enters
the
lead-out
groove, the pulse width becomes
narrow, and
IC1 thereby detects the fact that record play
has finished.
. Once end of play has been detected, IC1 pin 32
is switched to H level and pin 38 to L level (and
IC6 pin 8 is switched to H level and pin 7 to
L level), resulting in the geared motor starting
to rotate in the up direction to lift the tonearm
away from the record.
. As the geared motor
continues to rotate up,
the elevation cam pushes against the up detector
switch (89).
The subsequent chain of. events is
the same as described in steps 1 to 4 in "'Arm
Elevation Operation"'.
. The up indicator LED
(D15) is turned on as
soon as IC6 pin 7 is switched to L level.
And
when ICI pin 16 is switched to L level following
detection of end of play, the lead-out indicator
LED (D11) is turned on.
. After the tonearm has completed the up move-
ment and the geared motor
has stopped, IC1
pins 11 and 12 is switched to L level, resulting
in the tonearm commencing the lead-out opera-
tion moving
towards
the arm
rest (drive coil
activated).
. And as long as the auto repeat button (switch
S3) has not been pressed by this time, the tone-
arm will continue the lead-out operation.
When
the tonearm is near the arm rest, the rest sensor
(LED D51
and photo-sensitive transistor Q51)
applies signals to IC1, resulting in pin 40 being
switched to H level.
. The lead-out operation mode is maintained for
about 1.5 seconds
after detection by the arm
sensor
(1.5
seconds
being
sufficient
for the
tonearm to reach the arm rest).
. Then after 1.5 seconds, IC1 pins 11 and 12 are
reverted to H level and the drive coil deactivat-
ed, thereby completing the lateral tonearm lead-
out operation.
10. At the same time, IC1 pin 13 is switched to H
level, and turntable rotation is stopped by the
motor
ass'y (IC4) via Q6.
The quartz lock
LED (D9) is also turned off.
11. Pin 16 of IC1 is reverted to H level, resulting
in the lead-out
indicator
LED
(D11)
being
turned
off to mark completion
of the auto-
return operation.
Note that the tonearm completes the auto-
return operation in the up position, and the
up indicator LED (D15) remains on.
= Auto Stop Operation
1. If the START/STOP button (switch S5) is press-
ed during record play, IC1 pin 26 is switched to
L level, thereby
resulting in auto-stop
mode.
2. For details of operation, refer to ''Auto Return
Operation"' above.
When the START/STOP
button is pressed
for auto-stop operation, the auto-repeat mode
will be cancelled (if it has been set). IC1 pin
20 is switched
to H level, and the repeat
indicator LED (D14) turned off.
= Auto-repeat
1. When the repeat button (switch S3) is pressed,
IC1 pin 20 is switched to L level, resulting in
the repeat indicator LED (D14) being turned on,
and the PL-L800 being switched to auto-repeat
mode.
2. If the auto-return operation is started while the
repeat button is pressed, the tonearm will first
complete the up movement, and then commence
the lead-out operation, moving towards the out-
side edge of the record.
8. When
the tonearm
then
reaches the position
designated
by
the
DISC
SIZE
switch
(S2)
the size —
17cm
or 30cm
—
of the record
presently being played), IC1 identifies the tone-
arm lowering position according to the output
signals (first signal for 17cm position and second
signal for 30cm
position)
from
the lowering
position
sensor
(LED
D52 and photo-sensitive
transistor Q52).
4. When the tonearm reaches the lowering position,
IC1
cancels the drive coil current in order to
lower the tonearm for recommencement of play.
. When the repeat button is pressed during auto-
repeat mode, IC1 pin 20 is reverted to H level,
o
resulting
in
cancellation
of
the
auto-repeat
mode.
The repeat indicator LED (D14) is also
turned off at the same time.
This
auto-repeat
mode
is cancelled
auto-
matically if the auto-stop operation is activ-
ated, and also if the power is switched off.
= Tonearm Drive Circuit
1. The drive circuit diagram is outlined in Fig. 4-2.
The major components
in this circuit are the
differential amplifier and AMP1.
Tracking
shutter
a
eed
—
IC4 MB3614
Fig. 4-2 Tonearm drive outline
2. Amplification
signals from
the tracking sensor
are applied to the minus side of the differential
amplifier, while amplification
signals from the
tonearm
speed detector
generator are applied
to the plus side.
38. When the stylus is perpendicular to the carrier,
or
when
there are no
operation
signals (auto
lead-in, auto-return,
auto-cut, locate-in, locate-
out) from the control stage, the plus and minus
inputs of the differential amplifier are balanced
in
relation
to the
reference
voltage,
so
no
current will flow through the drive coil.
A,
a) a lela)
When
the carrier is moved
(by tonearm move-
ment), auto lead-in or auto-return signals, etc are
applied to the plus or minus side of the differ-
rential amplifier, resulting in loss of potential
balance
between
the plus and
minus
inputs,
and the consequent flow of current through the
drive coil.
Tracking Sensor Stage
1. The
structure
of the tracking
sensor
stage is
oo
a
bo
oo
outlined
in Fig. 4-2,
The major component
circuit is the bridge including two CdS elements,
R22, R23 and VR2.
VR2 is used to adjust the
potential difference between
A and B to zero
when
the stylus and carrier are at right angles
to each other.
. When
the stylus is perpendicular to the carrier,
the
beam
of light from
the
lamp
is passed
through
the
shutter
with
equal
amounts
of
light reaching the two CdS elements. The corres-
poinding
CdS
resistances
will,
therefore,
be
equal.
.If the stylus is moved
to either left or right,
there will be a change in the relative amounts of
light beamed onto the CdS elements, resulting
in the resistance in one CdS element being made
higher than the other, and thereby generating
a potential difference between A and B.
.In other words, the carrier remains still as long
as the stylus is at right angles to the carrier,
but is moved to left or right due to the flow of a
coil current obtained by amplifying the poten-
tial difference generated between A and B when
the stylus moves to left or right in respect to
the carrier.
Speed Switching
. Turntable
speed
is changed
by
pressing
the
SPEED
button
(switch
S1).
If the speed is
already
33 rpm,
pressing the
SPEED
button
will change the speed to 45 rpm, and vice versa.
. When the SPEED button (switch S1) is pressed,
IC1 pin 22 is switched to L level, resulting in
IC1 pin 14 also being switched to L level and the
motor
ass'y being activated
via IC4 for speed
switching purposes.
. At the same time, either LED D7 (for 33 rpm)
or LED D8 (for 45 rpm) is turned on by a signal
from the motor ass'y.
12
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