Orban 674A - EQ Bypass Switch Function; Highpass Filter and Output Buffer

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.
Several of
the circuit
boards
used
in the
674A Equalizer
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.
If
the
technician
has no
practical
experience
with
the
elegant
and
demanding
technique
of
removing
components
from
double-sided
PC boards
without
board
damage,
it is
wiser to
cut
each of
the
leads of an
offending
component
from its
body
while
the leads
are
still
soldered into
the
board.
The component
is
then
discarded,
and
each lead
is
heated
independently
and
pulled out
of
the board
with a
pair
of long
nose
pliers.
Each hole
may then
be
cleared of
solder by
carefully
heating
with a
low-wattage
soldering
iron
and sucking
out the
remaining
solder
with
a
spring-activated
desoldering
tool.
THIS
METHOD IS
THE
ONLY
SATISFACTORY
METHOD
OF CLEARING
A
PLATED-THROUGH
HOLE OF
SOLDER!
The new
component
may
now be
installed by
following the
directions
below
starting
with step
(4).
Use
the
following
technique
to
replace a
component:
|)
Use a
30
watt
soldering
iron to
melt the
solder
on the
solder
(underneath)
side of the
PC board.
Do not use a
soldering
gun
or a
high-wattage
iron!
As
soon as
the
solder
is
molten,
vacuum
it
away
with a
spring-actuated
desoldering
tool
like
the
Edsyn
"Soldapullt".
AVOID
OVERHEATING
THE
BOARD; overheating
will
almost surely
damage the
board by
causing
the
conductive
foil
to
separate
from the
board. Use
a pair of
fine needle-nose
pliers to wiggle
the lead
horizontally until
it can be
observed to
move
freely
in the hole.
2)
Repeat step (I)
until
each lead to
be
removed has
been
cleared of solder
and
freed.
3)
Now lift the
component
out.
4)
Bend
the leads
of
the replacement
component
until it
will fit easily
into
the
appropriate
PC board holes.
Using
a good
brand of
rosin-core
solder,
solder
each
lead
to the
bottom side of
the board
with a
30
watt soldering
iron.
Make
sure
that
the joint is
smooth and shiny.
If
no
damage
has
been done
to
the
plated-through
hole,
soldering of
the topside
pad
is
not necessary.
However, if
the
removal
procedure did
not progress
smoothly,
it
would be
prudent to
solder each
lead at the
topside
as
well
in order to
avoid
potential
intermittent
problems.
5)
Cut each
lead of
the
replacement
component
close to
the solder
(underneath)
side
of
the
PC
board
with
a
pair of
diagonal cutters.
6)
Remove
all residual
flux
with
a
cotton swab
moistened
with a
solvent
like
1,1,1
trichloroethane,
naptha, or
99%
isopropyl
alcohol.
The first
two solvents
are usually
available in
supermarkets
under
the brand
name
"Energine" fire-
proof spot
remover and
regular
spot remover,
respectively.
The
alcohol,
which
is less
effective, is
usually
available
in drug
stores.
Rubbing alcohol
is highly
diluted
with water
and is
ineffective.
24