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TC-766-2
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4.
High Voltage Power Supply for Solenoid Initial-
Energization
(Refer to Fig. 4)
The solenoids need a high voltage during pulling,
but a low voltage is adequate for hold.
1,
When stopped or during tape transport, Q706 is
ON
and
Q707,
708 ,are
in
the
OFF
state
providing
a
12V
power
supply
for solenoid
hold.
2.
In the hold condition, as the signal PAUSE (1)
enters point
@ from IC701, Q718 goes to the
ON
state and
the (+) side of C710
at +24V
suddenly
drops to zero
potential
so that the
(-) side (point @) becomes -24V.
Then the
signal passes through R712 and D708 where it
is discharged
at a time
constant
of R712 x
C710.
3.
Though
Q706
was ON,
as the PAUSE
signal
enters
point
@,
point
@
becomes
-24V
which creates an OFF state.
As a result, Q707,
708
are in the ON
state
and
provide
a high
voltage
power
supply
for
solenoid
initial-
energization.
(In
this
case,
turning
on
playback
muting.
Refer to page 11.)
4.
When
C710
has completed
discharging, Q706
goes to the ON state and Q707, 708 go to OFF.
The solenoid power supply returns to +12V for
hold use.
t2=RIMSXxC7I3
24V
Solenoids
tlSAIM4x
0713
@
lev
4
oy
Having a time constant
here prevents lamp
flicker from voltage
changes.
PAUSE signal 9
made large, the on-time for
playback muting becomes long.
(3 the value of resistor R715 is
(t2)
Fig. 4
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