Memory Circuit; Power Supply Circuits - Tascam 122 Service Manual

122
3-7 . MEMORY CIRCUIT
See Fig. 3-16.
Counter switch S696 is linke d to the counter
and is closed when the counter reads between
"900" and "999".
a. When the deck is in the rewind mode, a re ­
wind mode signal (H level) is output from pin
13 of system control IC U601.
b. Therefore, current flows from pin 13 of U601
to charge C507 via R502 and R518. Charging
takes place slowly because of the large charg ­
ing time constant.
c. The counter counts down as the tape is re ­
wound and, when it reaches "999", S696
turns on.
d. When 5696 turns on, C507's charge flows to
the base of 0691 via S696 and R691, turning
0691 on.
e. If the MEMORY switch is set to STOP when
0691 has turned on, a stop signal (L level)
is output from pin 2 (and pin 4) of U601 and
the deck enters the stop mode.
f. Pi n 4 (MEMO IN) of U601 has the function
that, if it becomes L level when U601 is in
the rewind mode, the rewind mode will be
released and the stop mode enabled. In the
deck, this terminal is connected to the STOP
IN terminal.
g. If the MEMORY switch is set to OFF, the col ­
lector of 0691 is open and S696 is on. The
tape will be rewound to the end and, when
the tape-end detect circuit detects the tape
end, the deck wi II enter the stop mode auto ­
matically.
•
~
R601 r
C60l
I
I- STOP
R606
r ~
2
4
C606;;;
PLAY
I N
REW 13
OUT
U601
R502
0504
STOP
IN
MEMO
IN
r
C507
h. If the MEMORY switch is set to PLAY when
0691 has turned on, a reproduce mode signal
(L level) is output from pin 1 of U601 and
the deck enters the reproduce mode.
i. The stop mode is entered automatically when
the tape has been rewound to the end before
the counter reaches "999", whether the
MEMORY switch is set to STOP or to PLAY .
3-8. POWER SUPPLY CIRCUITS
3-8-1 Main regulator
See Fig. 3-17.
Transistors 0517, 0519, 0520, and zener diode
D512 are the main components of the main
regulator. The output of the main regulator is
supplied to the amplifiers and also used as a
reference voltage in the regulated power supplies
of the motor and control circuits.
1) Equilibrium condition
a. The secondary voltage of the power trans­
former is full-wave-rectified by rectifiers
D541 - D544, then smoothed by capacitor
C520.
b. When power is not supplied to the regulat­
ed power supplies, 0517, 0519, and 0520
are off. (0519 is the currentampl l ifierthat
controls 0517 by amplifying variations of
weak control current flowing through
0520 described later. Here, the operation
of 0519 is not described.)
c. When the po~er supply to the regulated
power supplies starts, the base current of
0517 flows via path
CD .
Since 0520 is
still off at this time, current flowing
I MEMORY I
STOP
S691
OOFF
PLAY
069 1
Fig. 3-16 Memory circuit
20