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carefully
pull
the card
back from
the front panel so that
all
buttons
and LED's
are
clear
of their
holes.
The
card
may
then be
tilted
back
as
necessary, imagining
a
"hinge"
where
the vertical
card
meets
the
main
card.
To
reassemble
the
unit,
follow the
above
directions
in
reverse.
Before
tightening
the
screws
holding the vertical
card
to
the standoffs,
test
all
buttons to
make
sure
that
they do not bind against
the front panel
when
operated.
If
they
do, realign
the
vertical
card
as
necessary.
2)
Component Replacement
All
IC's
in
the
unit
are
socketed and can be
readily
replaced
from
the top surface
of the
main
board.
If
IC12
(the
N/R
chip)
is
replaced,
realignment
of
R132 (Thump
Null)
and
R134
(Gain Trim)
is
required.
If
1C31
or
IC52
(the
LED
photocouplers) are
replaced,
realignment
of the
corresponding gain trim
(R145 and R146)
is
required.
See Section
5 for
alignment
instructions.
WARNING
Disconnect
the
275A from
the
AC
power
line
before replacing
components
to
avoid the danger
of electric
shock.
If
any
of
the
CMOS
logic chips
are replaced, use reasonable
care
to
avoid
damage
due
to static electricity.
If
relative
humidity
is
below 50%,
use
a
grounded
workbench
and
make
sure that the
275A
chassis
is
grounded
to
it.
To
prevent
static
damage
to a chip,
do
not
touch
the
its
leads unless
you
are
also
touching the
workbench,
or
are
connected
to
it
through
a
standard high-resistance grounded
wrist strap. (Such wrist straps are
connected
to
ground through
1
megohm
or
more,
eliminating the
danger
of electric shock.)
If
the large
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
from
vibration
in
the
future.
3)
Replacement
Parts
If
you have
difficulty finding
parts for
this
or
any other
Orban
product,
Orban
Customer
Service stands ready
to
supply
you with the required parts
at a fair
price.
Please contact
us at the
address on the
title
page
of
this
Manual.
4)
Replacement
of
Components
on Printed
Circuit
Boards
It is
important
to use the
correct technique
for
replacing
components mounted on
PC
boards. Failure
to
do
so
will
result
in
possible circuit
damage
and/or
intermittent problems.
The
circuit
boards used
in
the
275A
are
of
the double-sided
plated-through
variety.
This
means
that
there are traces
on both
sides of the
board,
and
that the
through-
holes
contain
a
metallic plating
in
order
to
conduct current
through
the board.
Because
of the
plated-through
holes, solder
often creeps 1/16" up
into
the
hole,
requiring
a
sophisticated
technique
of
component removal
to
prevent
serious
damage
to the board.
4-2
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