Service manual
III-B.
MS-400A
Operation
The
controls
on
the
surface
of
the
front
as
the
usual
Listen
access
that
button
panel
are
used
during
normal
operation
controls.
These
switches
are
set
OFF
at
of
the
station;
the
controls
that
are
the
factory,
so
that
Talk
access
is
*
recessed
behind
the
front
panel
cover
normally
controlled
only
by
TALK
toggle
plate
are
normally
needed
only
during
switch
(10).
If
the
operator
requires
station
set-up.
both
Talk
and
Listen
access
when
the
Intercom
Select
button
is
engaged,
set
In
the
following
explanation
of
con-
the
talk
pre-sets
ON
for
the
channel(s)
trols,
the
boldface
numbers
in
paren-
desired.
*
theses
refer
to
the
diagram
of
the
MS-
400A
on
page
20.
Channel
Access
The
MS-400A
operator accesses
the
de-
The
MS-400A
has
two
headset
connectors
sired
channel(s)
by
using
the
Intercom
(1,2);
the
mic
input
of
the
upper
Select
and
Talk
toggle
switches.
Each
connector
is
switched
by
the
MIC
ON/OFF
channel's
Intercom
Select
switch
is a
*
switch
(3)
located
to
its
left.
When
push-on/push-off,
illuminated
switch.
neither
headset
jack
is
used,
the
mic
it
lights
dimly
while
engaged
(brightly
preamp's
gain
automatically
drops
to
when
a
Call
signal
is
received).
It
near
unity,
to
avoid
noise
pick-up
from
always
switches
the
Listen
path
of
its
the
unused
input.
(The
gain
of
the
associated
channel,
and
depending
on
the
switched
mic
input
may
be
lowered
by
setting
of
the
Talk
pre-set,
will
also
removing
either
R-15,
3
dB,
or
R-14,
5
switch
the
Talk
path.
The
Talk
path
may
dB.
DO
NOT
remove
both.)
The
headset
always
be
turned
on
with
the
Talk
toggle
connector
pin-out
is:
switch,
which
has
both
momentary
and
PIN
1--
MIC
COMMON
locking
positions.
PIN
2--
MIC HOT
PIN
3--
EAR
ELEMENT
COMMON
Stage
Announce
PIN
4--
EAR
ELEMENT
HOT
The
MS-400A
operator
presses
the
STAGE
*
ANNOUNCE
button
(11),
and
audio
from
the
While
using
the
MS-AOOA,
do
not
position
MS-400A's
mic(s)
feeds
to
the
rear
panel
the
headsets
within
two
feet
of
an
AC
S/A
connector
(12).
Normally,
the
Talk
power
transformer,
or
the
mics
may
pick
signals
to
the
intercom
lines
are
inter-
up
hum.
rupted,
but
you
may
add
a
jumper
across
the
switch
to
prevent
this.
If
the
optional
gooseneck
mic
(1)
is
installed,
it is
controlled
by
the
MIC
All
Page
ON/OFF
switch.
When
the
ALL PAGE
button
(13)
is
pressed,
the
MS-400A
operator's
voice
is
sent
to
The
HEADSET
VOLUME
(4)
and
SPEAKER
VOL-
all
four
intercom
channels
simultaneous-
UME
(5)
controls
permit
independent
ly,
whether
or
not
any
channel's
Talk
adjustment
of
the
intercom
audio
level
access
is
on.
All
Page
has
no
effect
on
*
in
the
station's
headset
and
speaker
any
of
the
station's
other
functions.
outputs.
The
SPEAKER
ON/OFF
switch
(6)
allows
the
SPEAKER
(7)
to
be
muted
in-
Sidetone
stantly
without
disturbing
its
volume
Sidetone
(the
voice
of
the
operator
setting.
heard
at
his/her
own
station)
must
be
carefully
controlled
to
avoid
acoustic
v
Programming
Channel
Access
feedback
and/or
system
Instability.
The
O
The
set
of
recessed
DIP
switches
that
MS-400A
has
a
front
panel
SIDETONE
con-
are
labelled
"Talk"
(8)
allows
each
trol
(14)
to
add
a
set
amount
of
side-
channel's
INTERCOM
SELECT
button
(9)
to
tone
to
the
unit's
headset/speaker
out-
be
programmed
for
Talk
access,
as
well
puts,
independent
of
any
channel(s)
that
*
21