Tascam 122 Service Manual page 16

122
3-4-2 Reproduce mode
See Fig. 3-12.
When the deck is in the stop mode, base current
is supplied to transistor OSOS via RS10, turning
it on. In the reproduce mode, the reel motor
rotates in the following sequence.
a. When a reproduce mode signal (H ' l evel,) is
output from pin 12 of U601 , 0601 and 0602
turn on.
b. 0601 activates the head base solenoid drive
circuit. When the head base solenoid com­
pletes operation, OS08 turns off, permitting
base current to flow through OS09 and turn ­
ing it on.
c. As OS09 is on, base current flows through
OS01 and turns it on. At the same time, cur­
rent flowing via path
CD
charges capacitor
CS04.
d. As OS01 is on, base current flows through
transistor OS04 via path
® .
and turns it on.
e. As OS04 is on, cu rrent is su pplied to the reel
motor via path @ and causes the motor to
run. At this time, the supply voltage of +13
V is directly applied to the reel motor so that
the motor drives the reel disk with a large
starting torque so that the tape is tight.
f. As current on path
CD
charges CS04 and its
charge rises, the voltage at the base of OS06
rises and its base current increases; OS06 is
turned on completely in about 80 msec. Now
the base current of OSOS decreases since its
base level falls from +13 V, divided by RS10
REW 0:
OUT
R622
U601
F
~~~
1)",,-5 -'V.
iv ­
R6ZO
and RS09. This results in a decrease in OSOS's
collector current (the current supplied to
the motor) and in the voltage applied to
the motor. Thus the torque of the motor is
reduced and the reproduce mode is stabilized.
3-4-3 Rewind mode
See Fig. 3-12.
When the rewind mode has been enabled, a
rewind mode signal (H level) is output from pin
13 of U601 and base current flows through
OS01 via resistor R622, turning on OS01.
OS04 turns on immediately since its base cur­
rent f.lows along path
® .
When OS04 is on, a
large current is supplied to the reel motor via
path @ , driving the motor at a high speed. Our­
i1 ng the rewind mode, OS06 remains off.
3-4-4 Fast-forward mode
See Fig. 3-13.
When the fast-forward mode has been enabled,
a fast forward mode signal (H level) is output
from pin lS of U601 and base current of tran ­
sistor OS02 flows via resistor R620, turning
OS02 on. As OS02 is on, base current of tran ­
sistor OS03 flows via path
CD ,
turning OS03 on.
Now +13 V is applied to the reel motor, the
large current flowing via path
®
causes the
motor to run at a high speed. The direction of
the current is reversed in the fast-forward mode
to that in the reproduce and rewind modes so
the direction of motor rotation is reversed.
+13v
'.::...3
~~-+r
t-+---------~~-----------II I
- - - H '
Fig.3-13 Reel motor drive circuit {fast-forward mode}
16