Automatic Rewind Circuit - Teac C-1 Service Manual

14
TAPE TRANSPORT SECTION
2-8 AUTOMATIC REWIND CIRCUIT
The automatic rewind operation is selected in three func-
tions of (1) PLAY, (2) OFF and (3) STOP by the switch
S704.
(1) PLAY
The tape cycle repeats play and rewind as follows.
PLAY > TAPE END ~ AUTO REWIND > Stop at
count "999" > AUTO PLAY > ......
Assuming that the index counter is reset (to ''000"') and the
deck is set in the PLAY mode. When the tape reaches the
the end in the PLAY mode, the tape end detection circuit
operates and Q509 outputs a high level signal. This high
level signal is sent to pin 10 of the SYS-CON via route (1).
The status in which a high level signal is present at pin 10 is
equal to the condition when the REWIND button is de-
pressed. Thus, the deck is set in the REWIND mode.
In the PLAY mode, pins 20 and 21 are at the low level,
Q521base is also low and Q521 is off. Therefore, Q520 is
held off even if Q509 turns on and Q520 base goes high.
Pin 21 goes high when the PLAY mode is changed to the
REWIND mode. The output of pin 21 biases Q507 base via
route (2) and Q521 base via route (3), and turns on each
transistor.
The index counter counts down after the tape is rewound.
The counter switch S695 closes when the counter reaches
"999". The switch S695 is closed while the counter counts
from "900" to "999",
Current flows in Q513 via route (4) and Q508 turns on.
Q507 has base bias so when Q507 emitter falls to ground
potential with Q508 turned on, Q507 turns on. At the
same time Q506 is also turned on by the current in route
(5).
With Q506 turned on, a high level signal is supplied to pin
8 via route (6) and the deck is set in the PLAY mode.
When the operation mode is changed from REWIND to
PLAY, about 200 milliseconds delay time elapses. (Refer
to the paragraphs 2.5 and Fig. 13)
The current in the route (2) is interrupted when the opera-
tion mode is switched from REWIND to PLAY as described
avobe. Thus, the charge in C512 is rapidly discharged by
route (7).
If the REWIND button is depressed immediately after the
PLAY mode is selected, current flows again in C512 (in
route (2)). However, because of the charging time con-
stant, the potential at the point (A) increases gradually.
Therefore, even if S695 closes again and Q508 turns on,
Q507 is not turned on and the PLAY mode is not automa-
tically selected. In this case, the tape is rewound to the end
regardless of the count of the index counter.
When the tape end is detected, Q509 turns on and a tape
end signal is transmitted in routes (1) and (8).
In the REWIND mode, Q521 is turned on by the current in
route (3) and thus Q520 is set in the standby condition.
When Q520 base is biased by the current in route (8), Q520
turns on and Q516 is turned on by the current in route (9)
and supplies a high level reset signal to pin 2 of the SYS-
CON via route (10).
A rewind signal is also applied to the SYS-CON via route
(1) at this time. However, since the reset signal has priority
over all other input signals, all SYS-CON outputs are reset
and the deck is set in the STOP mode.
(2) OFF
When the switch S704 is in the OFF position, the output of
the tape end detection circuit is connected to the STOP
button circuit. The STOP mode is selected in the PLAY, F.
FWD and REWIND modes when the tape reaches the end.
(3) STOP
Tape cycle is as follows.
PLAY > TAPE END > AUTO REWIND ~> STOP (at
count '999"*)
In the PLAY mode, the tape end signal sets the deck in the
REWIND mode via route (11). When the count '999" is
reached in the REWIND MODE, Q508, Q507 and Q506
turn on, a high level signal is applied to the SYS-CON via
the route (12) and the deck is set in the STOP mode.
When the tape end is detected before the count reaches
"999" in the REWIND mode, the reset circuit operates and
sets the deck in the STOP mode as previously described.