Tascam 122 Service Manual page 11

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122
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DRIVER
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INO LOAD I
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13 V
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+ 39V
U601
FA S T
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OUT
0610
C516 0511 R5 36
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0510
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(D®
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L _ _ _ _ _ _ _ _ _ _ _
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Fig. 3-4 Fast solenoid drive circuit
i.
Current is sti" flowi ng through the fast sole ­
noid via path
CD
even though path @ is cut
off. Once the fast solenoid is energized by the
strong current on path
@
, this weak current
flowing via path
CD
can hold it on.
Thus a high vo ltage (strong drive current) is
supplied to the solenoid when energizing it while
a low supply voltage (weak current) hold it on.
This ensures solenoid operation by generating
a strong mechanical force and prevents the
solenoid from heating up by reducing the hold ­
ing current.
The circuit which switches the supply voltage of
the solenoid is called the flashing circuit.
When a fast mode is released (the STOP button
is depressed during fast-forward or rewind
mode), the following sequence of operations
takes place.
j. As soon as a fast mode is released, pin 14 of
U601 tu rns to L level.
k.0605 turns off, because its base current is
cut off.
I. As 0605 is off, 0515 turns off, as its base
current is cut off.
m.As 0515 is off, the solenoid is reset, because
its holding current which was flowing via path
CD
is cut off. At the same time, C516 dis­
charges via path
®
to prepare for the sub­
sequent start of a fast mode.
3-3-3 Head base solenoid drive circuit
See Fig. 3-5.
The head base solenoid operates during the re ­
produce (record/reproduce) and pause (record/
pause) modes. In the reproduce mode, a repro ­
duce mode signal (H level) is output from pin
12 of U601. In the pause mode, a pause mode
signal (H level) is output from pin 11 of U601.
In both cases, the H-Ievel signal causes base
current of transistor 0601 to flow so it is turn ­
ed on. The part of the head base solenoid drive
circuit after 0601 is exactly the same as the fast
solenoid drive circuit described in the previous
section . Since these circuits operate in the same
way, the description is not repeated. Note
that the time during which the solenoid is
energizied by the high voltage from the flashing
circuit (capacitor C516 and resistor R536 deter­
mine this) is approximately 400 msec, longer
than the 100 msec of the fast solenoid. The
reason is to ensure operation of the head base
solenoid as its mechanical load is much greater.
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