Capstan Motor Circuit; Tape-End Detection Circuit - Tascam 122 Service Manual

122
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3-5. CAPSTAN MOTOR CIRCUIT
'See Fig. 3-14.
The capstan motor rotates in the reproduce
(record/reproduce) and pause (record/pause)
modes. Its torque is transmitted to the flywheel
by a belt to drive the flywheel and capstan shaft.
In both the reproduce and pause modes, 0514 is
on to energize the head base solenoid. When
0514 is on, base cu rrent flows through transis­
tor 0692, turning it on. Now the 0 V line of the
capstan motor servo amplifier is shorted to the
ground line of the power supply circuit. The
servo amplifier is activated and the motor starts
to rotate. The speed of the capstan motor may
be switched between 'standard' (tape speed:
4.76 em/sec) an.d 'high' (9.5 em/sec) by SPEED
switch S4-2.
PLAY 12 R612
OUT
PAUSE II R613
OUT
U601
HEAD BASE
T
0694 SOLENOID
L692
3-6 TAPE-END DETECTION CIRCUIT
See Fig. 3-15.
The ring magnet, shown in Fig. 3-15, is mount­
ed on the counter pulley shaft and rotates while
the tape is running. Variations in the magnetic
field caused by the rotation of the ring magnet
turn reed switch S693 on and off. This means
that, when the tape is moving, the reed switch
turns on and off repeatedly.
When the reed switch turns on while the tape is
running, the charge from capacitor C609 flows
through the base of transistor 0607 via path @ ,
turning it on. When the reed switch turns off,
0607 turns off, as its base current is cut off. At
this time, C609 discharges via path
@
. Thus,
while the reed switch is turning on and off re­
peatedly, 0607 also turns on and off repeated-
r - - - - - - - - - - - - - + 3 9 V
,--;:::;;;;;;;:::;:-T----
+
13V
I
SPEED
+
54-2
-"""'>--.!..jY
SERVO
AMPLIFIER
H
FLASHING
CIRCUIT
CAPSTAN
MOTOR
M692
Fig. 3-14 Capstan motor circuit
18