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In
the
424A,
power
is
supplied
from
the
CHANNEL
A
board
to
the
CHANNEL
B
board through
a plug
which
is
simply
pulled
off.
In
addition, the
two
boards
are
interconnected
by
means
of
wire
leads
connected
to
the
COUPLED/INDEP
switch.
The
two
wires
may
be
unsoldered
at
the
COUPLED/INDEP
switch,
noting
which
wire
goes
to
which
terminal.
(This
switch
is
soldered
to
floating
pads on
the
board
to
secure
it
mechanically.
However,
it
does
not
connect
to
any
printed
wiring.)
Reassembly
is
performed
in
the reverse
of
disassembly.
(If
notations as
to
which
wire
goes
to
which
terminal are misplaced, consult the
schematic
at
the
back
of
this
manual
to
deduce
the correct
wiring.)
Circuit boards should be fastened
using eight
screws
removed
above, taking care
to
center the switch shafts
in
their
holes
to
avoid
binding.
When
the
knobs
are reattached, they should
first
be
partially
tightened, leaving a
small
clearance
between
the
knob and
the
panel.
Once
partially
tightened,
each
knob
should be
turned
so
that
it
aligns
with
the
markings on
the panel
at
the
counterclockwise
stop of
the pot.
Once
properly
aligned,
each
knob
should
be
firmly
tightened.
Then
replace
the
snap-on
caps,
accurately
aligning
the
marking on
the
cap
to the
marking
on the
knob.
The
meters
should be
reconnected
as
necessary,
and
the
LED's
reinserted
in
their
color-coded
lenses.
Operation
of
the
unit
should
be
checked
before
the
covers
are
installed.
Lamp
Replacement:
Lamps
supplied
with
the
422A/424A
are
a
long-life
type
which
are operated below
their
rated voltage.
They
are not
expected
to
fail
in
the
field
under normal circumstances.
If
they do
fail,
replacement
requires
removing
the
meter
bracket
after
removing one
circuit
board.
The
correct
replacement
is
a
#1847
lamp; a
#47 lamp
may
be substituted
in
an
emergency,
although
its
life
is
shorter and
it
may
therefore require inconvenient future
replacement.
(If
one lamp
is
replaced,
it
may
be
advisable
to
replace
the
other
to
avoid
future
work.)
Component
Replacement:
All
IC's
in
the
unit
are
socketed and
can
be
readily
replaced from
the top
surface
of
each
board.
Realignment
is
required
if
IC5, IC6,
IC7, IC8, or
ICO
is
replaced.
Other
components
are
soldered
in
place,
and
may
be
replaced
following
the
instructions
in
Replacement
of
Components
On
Printed
Circuit
Boards immediately
below.
The two
potted
modules
on
each board
are
not
field-repairable,
and
must
be
replaced
in
their entirety.
While
either
module
can
be replaced without realignment
of
the
unit,
diagnosing
failures
in
the
Compressor/Limiter Timing Module can be
tricky
and
is
best
left
to
the factory unless
you
are
willing to
risk
the
expense
of
replacing
a possibly
good module!
If
filter
capacitors are
to
be
replaced, fasten
them
securely
to
the board, using
the
original
factory
installation
as
a
model.
This
will
prevent
their
breaking
loose
in
the future
from
vibration.
28
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