Timer Control Circuit - Teac C-1 Service Manual

16
TAPE TRANSPORT SECTION
2-9 TIMER CONTROL CIRCUIT
The timer control circuit turns AC power on and off
supplied to C-1 bya timer switch external to the tape deck,
and actuates the recording (playback) operation.
(1) Timer start circuit
Refer to Fig. 20. When the REC TIMER switch S692 is
off, Q519 base is grounded and thus Q519 does not oper-
ate. When the deck is powered with S692 turned on, cur-
rent flows in C517 via routes (1) and (2). Q519 is turned
on by the current in route (1). Q519 collector current
turns on Q518. Q518 supplies high level signals to pin 4
and 8 of the SYS-CON (via routes (3) and (4)). As de-
scribed in the paragraphs 2.1, when the deck is powered,
Q517 is turned on via route (5) and Q516 is turned on via
route (6) and an initial power reset signal is supplied to the
SYS-CON via route (7). The reset signals have priority over
all other input signals. Thus, the SYS-CON does not oper-
ate as long as it is supplied with the rest signal.
When current flows in C517, the potential at point (B) is
greater than that at point (C) because R556 is larger than
R555. Therefore, when the potential at point (A) falls as
C517 charging proceeds, Q519 is held on for a longer time.
This relationship is illustrated in Fig. 19. As seen from Fig.
19, signals are left in routes (3) and (4) even after the SYS-
CON reset signal has stopped. Thus, the deck is set in the
REC-PLAY mode.
If the record protection tab is broken off, the PLAYBACK
mode is selected instead of the RECORD mode.
When the power supply is interrupted, the charge in C517
is rapidly discharged via route (8) and C517 is set ready for
the next start.
Intermittent recording (or playback) can be repeated any
time until the tape reaches the end.
Current flows in route (1) only when the power switch is
turned on. Thus, the deck mode is unchanged even if the
REC TIMER switch is set to the "IN" position after the
power switch is turned on.
+13V
Ov
OFF
Q519, O5i8 ON
OFF
O517, O516 ON
HIGH
® LOW
HIGH
© Low Approx.
4 Sec Approx. lOOmSec
POWER ON
®
(2) Timer stop circuit
The captsan motor rotates continously even after the tape
stops at the end in ordinary recording or playback opera-
tion without using the timer.
There is usually nobody present during timer controlled
recording, so it is undesirable that the captsan motor should
rotate after the tape reaches the end. To avoid this, the
circuit is designed so that the captsan motor also stops
when the deck stops operation at the tape end during timer
recording. (Refer to Fig.21) Q904 to Q906 and their
peripheral circuits comprise a constant voltage circuit
which supplies power to the captsan motor.
Voltage values indicated in the circuit are those obtained in
the course of recording or plyback. Values put in(_ ) indi-
cate values obtained when the timer is stopped. These
voltage values are approximate.
While the deck is operating in the REC/PLAY mode, some
voltage is applied to the anode of SCR D543 via routes (9)
and (10). However, since Q509 of the tape end detection
circuit is off at this time, SCR is cut off. When the tape
end detection circuit operates at the tape end and Q509
tums on, current flows in the collector of Q509 via route
(11).
Then, a very weak current flows from the gate to the
cathode of SCR (via route (12)) and the SCR becomes
conductive. With SCR turned on, current flows in routes
(9) to (13) and (10) to (14). As current flows in routes
(10) to (14), Q516 turns on and resets the SYS-CON.
Then, the deck is set in the STOP mode. When current
flows in routes (9) to (13), the potential at point (F)
becomes about 2.2V. Thus, no current flows in the base
of Q905 (and Q904) and the constant voltage circuit out-
puts no voltage. Power supply to the captsan motor circuit
is stopped, and the captsan motor therefore stops. Even if
the deck is set in the STOP mode and Q509 is turned off
again, SCR is held conductive because a very weak current
flows in the SCR via routes (9) to (13). To reset the timer
stop condition, set the REC TIMER switch to the '"OUT"
position or turn off the deck power switch and turn off the
SCR temporarily.
= @x R557/(R556+R557)
© 4% @x R5§5/(R554+R555) ©+2@
THRESHOLD
LEVEL
& (vee OF O5I7 or O519)+( vp OF D522 or D557)
RbL4av
REC ond PLAY SIGNAL
RESET SIGNAL
T-1305
Fig. 19 Rec/Play and Reset Timing Chart