I
122
,----,
I
DRIVER
I
;mSHIN;;CIRCUI~
- - - - -
--;
INO
LOAD
I
I
I
I
I
+ 13 V
I
I
I
I I
+ 39V
U601
FA S T
0:
1
_4
-+I--.---H'
OUT
0610
C516
05
11 R536
,------,
, I I
l@
I •
0510
t I
(D®
I
L
___________
...J
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 voltage (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
hold
i
ng
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.
11
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