Advertisement
Most
circuit
cards
used
in
OPTIMOD-TV
are
of
the
double- sided
plated- through
variety. This means that there are traces on both sides of the card, and that the
through- holes
contain a metallic plating in
order to conduct
current
through
the
card. 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 card.
If
the
technician
has
no
practical
experience
with
the
elegant
and
demanding
technique
of
removing
components
from
double- sided
PC
cards
without
card
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
card.
The
component
is
then
discarded, and each lead is heated independently and pulled out of the card 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 IN THE FIELD!
The
new
component
may
now
be
installed
by
following
the
directions
below
starting with step ( 4).
Otherwise, use the following technique to replace a component:
1)
Use
a 30
watt
soldering
iron
to
melt
the
solder
on
the
solder
side
(underneath) of the PC card. 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 CARD;
overheating will almost surely damage the card by causing the conductive foil to
separate from the card base.
Even
with care, you are likely to blister the enamel solder- mask coating on the
card, which, in most cases, is no cause for concern. The coating exists mainly to
prevent
moisture
from
condensing
between
the
traces
and
to
simplify
wave-
soldering.
2)
Repeat
step ( 1)
until
each lead to be removed has
been
cleared of
solder
and freed.
3)
Now
release
the component by gently
wiggling
each
of
the leads
to
break
solder webs. Then lift the component out.
4)
Bend the leads of the replacement component until they will fit easily into
the
appropriate PC card holes. Using
a good brand of
rosin- core solder, solder
each
lead to the bottom side of the card 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 card 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.
F-12
Advertisement
