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Fig.
13-61
Through
switch functions
Table 13-14
Through
switch
position
POWER
VIDEO
•
AUDIO SW
OFF
ON
NORMAL
THROUGH
POSITION
THROUGH
NORMAL
THROUGH
*
THROUGH
switch
circuit
The
THROUGH
switch
circuit
consists
of the
THROUGH
relay
(RY102),
a charge storage
circuit
(D140,
D138,
C406, and C421),
a driver
(Q401
and Q402),
a
switch
position detector
circuit
(RY102(7/8),
IC113(3/4),
and R405),
a
pulse
generator
(IC113
(1/4, 2/4,
4/4)
and
delay
cir-
cuit),
a
timing
circuit
(Q403, D139, R406, R407,
and C402),
a
rectifier
(D119,
D118, C403, and
C404),
and
a video/audio
switch (S101).
The
ope-
ration
of
this circuit
is
outlined
below
in
respect to
the
timing
chart
(see Fig.
13-63).
If
the
power
is
assumed
to
be
switched
on
at
time
tl
with
RY102
in
the
THROUGH
position
and SI 01
in
the
NORMAL
position
prior to
time
tl,
an
AC
waveform
will
appear
at
"a",
and "g"
is
rectified at
a negative potential
(about
—IV)
by
the
rectifier.
Q403
is
turned
off,
and
"h" becomes
the
regulated
power
line
voltage
(H
level)
due
to
R408.
D139
is
off,
and
"i"
is
increased
because of the
R406/C402
time constant (where
R406>R407).
When
"i" reaches the
IC113(3/4)
threshold
level
(t2),
"j"
is
changed
to L,
and
"h"
is
connected
to
"k"
since
RY102
is
in
the
THROUGH
position,
resulting in
"k"
being
changed
to
H,
and
"1"
to
L.
Therefore,
"m"
is
also
changed
to
L.
If
"j"
is
changed
to
L
at t2,
"n"
is
changed
to
H
(since
"m"
is
also at L), resulting in
Q401
being turned on,
PM2
being
activated
(since
"p"
is
changed
to L),
and
RY102
being
changed
to
the
NORMAL
position.
If
RY102
is
changed
to
NORMAL
position
at
t3,
"j"
is
connected
to "k",
resulting
in
"k"
being
changed
to
L
and
"1" being
changed
to
H,
thereby
increasing
the
level
of
"m"
(in
accord-
ance with the
delay
circuit).
When
the
"m"
level
reaches the
IC113
threshold
level,
"n"
is
changed
to
L,
Q401
is
turned
off,
"p"
is
changed
to H,
and
the
PM
is
switched
off,
thereby completing the
plunger
drive
operation
at
t4.
Since
current
is
passed to
PM2
from
C406
during the t2 thru
t4
interval,
the
"e"
level
decreases,
but
is
increased
again
according
to
the
R414/C406
time
constant
after
t4.
Since
"h"
is
at
H
and
"o"
remains
at
L
during
this series
of
operations,
PM1
is
kept
off.
If
SI 01
is
switched
to
the
THROUGH
position
at
t5,
the current
circuit
is
cut,
and "g"
is
increased
sharply since
C403
is
charged
up
via
R413.
Q403
is
turned
on,
"h"
is
changed
to
L,
D139
is
turned
on,
and
C402
is
discharged,
resulting in
"i" being
changed
to
L
and
"j" to H. Since
RY102
is
still
in
NORMAL
position
at this
time,
"k"
is
changed
to
H
and
"1"
and
"m"
are
changed
to
L, resulting
in
"h" and
"m"
being changed
to L,
"o"
being
changed
to H,
Q402
being turned on,
and
followed
by
PM1
also
being turned
on
with
RY102
being
switched
to the
THROUGH
position.
Hence, with
RY102
in
THROUGH
position
at
t6,
"k"
is
changed
to
L
since
it is
connected
to "h", "1"
is
changed
to H,
and
"m"
is
increased.
When "m"
reaches
the
IC113(2/4)
threshold
level,
"o"
is
changed
to
L,
Q402
is
turned
off,
and
PM1
is
turned
off
to
complete
the plunger
drive
operation
at
til.
If
SI 01
is
switched
to
NORMAL
position
at
t8,
"g"
becomes
negative,
and
the
same
sequence of
events
from
tl
to
t4 to switch
RY102
back
to
NORMAL
position.
And
if
the
power
is
switched
off
at
tl2,
"a" becomes
zero,
"g"
is
increased,
and
RY102
is
switched
back
to
NORMAL
position
by
the
same
sequence of
events
from
t5 to
t7.
Due
to
the regulated
power
supply
and
the charge storage
circuit,
the
switching
is
not
effected
by
a
reduction
in
the
"b"
level.
122
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