Sony TCM-8EV - Page 6

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TCM-SEV
SECTION 2
CIRCUIT DESCRIPTION
CIRCUIT DESCRIPTION
This set utilizes a
BBD (Bucket Brigade Device) IC
in
order to prevent the beginning audio from being
recorded brokenly during VOR recording , by delay-
ing
the audio signal.
Fig. 1
is a block diagram of the audio signal delay.
The audio signal is
output from IC101 pin@ ,
passes
the R201, 202 attenuator and Q201 low pass
filter,
and is input to IC201 pin G) . The R201 , 202
attenuator attenuates the signal so that it does not
go over IC201 maximum input level of about - SdB.
LOW PASS
FILTER
0201
AUDIO
SIGNAL
DELAY
IC201
Q201 low pass filter operates at cut-off frequency of
4kHz so that it does not go over the clock pulse and
beat which operate IC201 , 202. IC201 , 202 form an
audio signal delay 1024-stage BBD IC. On this set,
these
two ICs delay about 85msec . The delayed
signal has
the amount attenuated at R201, 202
amplified at Q203, it passes Q202 low pass filter and
is input to Q 102 , 103 recording amp . Q202 low pass
filter
is to cut the clock pulse so that it is not super-
imposed on the signal at the BBD IC.
AUDIO
SIGNAL
DELAY
AMPLIFIER
0203
LOW PASS
FILTER
0202
RECORD
AMPLIFIER
0102 . 103
IC202
Fig. 1.
Audio signal delay block diagram
--Pig. 2 shows the circuit which controls on and off
of the motor and bias oscillation during VOR record-
ing. The audio signal output from ICl0l pin @ is
amplified at Q301 . When the level of the audio signal
input to Q301 is large, Q302 base potential drops
and Q302 goes on . When this happens, IC301 pinG)
voltage goes higher than pin Q) and pin (D goes high.
Then Q305 , 303 turn on , and supply power to servo
IC
(IC601) and bias oscillation transistor (Ql0l).
Q306 is a transistor for switching VOR recording
sensitivity,
and when VOR recording sensitivity is
low it turns on and attenuates the audio signal input
to Q301. Also, when there is no audio signal from
the microphone, and the motor bias oscillation is
stopped immediately, the last audio is not recorded
(the audio signal is delayed about 85msec for VOR
recording), and further, if on / off is repeated at too
short intervals, the playback sound will be hard to
heas, so C3 04 maintains IC301 pin G) at high for
about 2- 3 sec onds to prevent this.
B+
B+
c--
HEAD
AUDIO SIGNAL
0303
TO MOTOR SERVO
0306
2SCl623
V0R SENSITIVITY SWITCH
0301
2SC623
V0R AMP
005
0. 22
003
0. 01
R3 06
1k
O0 G R305
0. 001 llk
R307
81
R 308
470,
0302
2SAll62
V0R SW I TCHING
R310
I0k
R3 09
4 7k
+ C304
4.7
, ov
IC3011l/2l
NJM2903M
V0R S WITCHING IC 0 MFIIRTER I
Fig. 2. Motor, Bias oscillator control circuit
-6-
2SAll62
BIAS OSCILLATOR
0303 V0R
SW ITC HIN G
CIRCUIT
0305
2SCl623
V0 R
CO NTR OL
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