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Fostex A-8 - Page 15

Fostex A-8
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£20
switches
on
when
Q19
is
off,
to
act
as
a
braking
circuit
by
absorbing
the
counter
electromotive
force
from
the
motor.
When
the
PLAY
button
is
depressed,
the
"L"
output
from
U9-17
is
passed
through
an
inverter
and
applied
to
U8-5;
on
the
other
hand,
as
the
signal
to
08-6
is
also
"H"
,
the
output
of
U8-4
is
an
"L"
but
on
being
inverted
by
U8-10,
the
"H"
level
output
is
applied
to
Q12.
Q12
and
Q13
is
then
switched
on
and
its
output
applied
to
the
integration
cir
cuit
of
R94,
R95
and
C47/C48.
At
the
same
time,
the
"H"
output
of
U8-10
makes
the
output
of
U8-3
go
to
"L"
thus
switching
off
QI
5.
By
this
alternating
switching
of
Q13
and
Q15,
the
integration
circuit
constant
is
affected
and
output
duty
of
comparator
ull-8
is
changed.
As
a
result,
the
motor
revolution
changes
from
1,000
rpm
to
2,000
rpm,
and
consequently,
the
TACH
output
of
1,
200Hz
rises
to
2,400Hz.
The
TACH
output
at
1,000
rpm
is
about
350mV.
When
the
shut
off
switch
is
on
(left/right
tension
arm
in
down
position)
,
Q17
is
switched
on
to
force
the
UI
1-1
output
to
"L"
which
then
switches
off
Q19
and
the
motor
is
stopped.
However,
the
motor
will
continue
to
run
in
the
EDIT
mode,
even
if
the
shut
off
switch
is
on,
as
the
EDIT
switch
is
in
series
with
the
shut
off
switch.
4.5
INTERMITTENT
SOLENOID
DRIVE
CIRCUIT
Two
plunger
solenoids
are
used
in
the
tape
transport
mechanism.
One
is
for
activating
the
pinch
roller
in
the
play
mode
and
releasing
the
brake,
and
the
other
for
activating
the
lifter
in
the
fast
forward
or
rewind
modes
and
also
to
release
the
brakes.
Output
pins
#17
and
#18
of
U9
goes
to
"L"
when
the
PLAY
button
is
depressed.
The
"L"
level
from
pin
#17
is
inverted
to
an
"H
”
level
by
U10-4
and
applied
to
Q44
to
switch
on
both
Q44
and
Q45.
On
the
other
hand,
the
"L"
level
from
pin
#18
switches
off
Q39
which
then
starts
to
charge
C34
by
D61,
R172
and
R171.
This
charging
of
C34
switches
on
Q40
but
is
switched
off
after
a
certain
length
of
time
which
also
switches
off
Q41.
Therefore,
when
Q45
is
switched
on,
the
PLAY
solenoid,
Ll,
is
energized
by
the
+24V
DC
flowing
through
Q41,
D64,
Ll
and
Q45.
When
Q41
is
switched
off,
the
+24V
DC
drops
to
+16V
DC
as
the
current
will
now
flow
through
D65,
Ll
and
Q45.
When
the
F.FWD
button
is
depressed,
output
pins
09-22
and
U9-18
goes
to
"L"
level;
and
when
the
REWIND
button
is
depressed,
pins
U9-23
and
U9-18
goes
to
"L"
level.
The
signals
from
U9-22
and
U9-23
are
applied
to
Q42
via
the
OR
gate
of
D46
and
D47.
15

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