Tape Loading Circuit - Teac C-1 Service Manual

10
TAPE TRANSPORT SECTION
2-3 TAPE LOADING CIRCUIT
C-1 adopts the dual capstan drive system. If a cassette tape
is slack, it may cause intermittent sound or level fluctua-
tion, or even disable recording or playback. To prevent
this, a circuit which automatically pull the slack in the tape
is provided. This circuit operates when a cassette is loaded
after the deck is switched on or when the deck is switched
on after a cassette is loaded.
(1) When a cassette is loaded after the deck has been
switched on.
When a cassette is loaded, S693 is switched ON. Then,
current flows in C652 via route (1) and turns on Q659
until C652 is charged. With Q659 on, a part of the collec-
tor current (in the route (3)) turns on Q660 and supplies
current to the reel motors (route (4)). The current in
route (2) clamps the base of Q660 at about 2.5V and limits
the emitter potential to about 1.8V.
The other part of the Q659 collector current (in route (5))
is sent to the brake solenoid drive circuit and used to drive
the brake solenoid.
Since C522 is being charged in this time, the solenoid is
operated intermittently as previously described.
When the solenoid is operated and the reel table brake is
released, the reel table rotates to pull the slack in the tape
because weak current flows in the right and left reel motors
as previously described.
Since equal current flows in the right and left reel motors,
the tape is balanced and slack eliminated. The torque at
this time is very small, and can not damage the tape.
The time during which the current flows in the reel motors
is a little longer than the time during which the brake is
released due to different operating voltage between the reel
motor circuit and the solenoid drive circuit. The signal
in the route (9) is used to inhibit the SYS-CON output
while a cassette tape is loaded. The signal in the route (10)
is used to hold the tape end detection circuit while a
cassette tape is loaded.
(2) When the deck is switched on after a cassette is loaded.
With a cassette loaded, S693 is turned on.
When the power switch of a deck is turned on in this condi-
tion, the DC power supply rises and current flows in route
(1). Then current flows in routes (2) to (5), and (9) and
(10) in the process described in (1).
C522 is still not charged by this time. Current does not
flow in route (7), and it is impossible to operate circuits on
and after Q524. To turn on Q524, bias current is supplied
to Q524 via route (8) for a short time until C524 has
charged. When Q524 turns on, Q525 turns on and then
Q534 turns on and supplies +24V to the brake solenoid to
operate it.
The other operations are the same as those on (1). Routes
(11) and (12) are used to discharge C652 and C524, respec-
tively.
0527 R577 TAPE END DETECTING CIRCUIT
INHIBIT SIGNAL
(0) (TO O51! BASE)
[SYS-CON "OUTPUT [BRAKE SOLENOID DRIVE CIRCUIT. —=~—SOC=C<"C~S~S*C'"<=CS~S*StSSS
INHIBIT CIRCUIT yeav
(See FIG.6) |
1s
BB
+10V
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Q5!13
(Dd R546
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ee ree > ce ee cS mowed
BRAKE
SOLENOID
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OFF ON ai 0660 rane
$693 0 p I 066! R674 «REEL MOTOR 18 Sec
CAPSTAN
MOTOR SW BRAKE
T~1297
290.
mSec 1Sec
Fig.11 Tape Loading Circuit