( Continued from page 51)
after warming up, the problem
re-appeared . The faulty IC w as
replaced and the circuit was check-
ed by heating up the horizontal ball
circuit with a heat gun . Problem
solved .
Another area which can drive any
well-adjusted technician up the wall
is a bad plated·thru hole . If a poor
plating job was done at the time of
manufacture , the printed circuit
board could develop intermittents.
Usually this type of fault mani-
fests itself when the printed circuit
board is bent or twisted. The
problem with this type of fault is to
isolate the area where the fault
occurs. If the fault can be made to
come and go when the printed
circuit board is bent or twisted, you
have a good chance of finding the
fault. Try holding down one section
of the printed circuit board and bend
the rest of the board. If the fault
comes and goes, the fault must be
in the portion of the printed circuit
board you are bending. By applying
this technique to different parts of
the board, the area where the fault
is occuring can be located.
Once the area has been isolated, a
physical inspection should take
place . Look at the plated-thru holes
South American
(Con tinued from page 45)
He-nationalizing-- Although
the
process is not specifically contem-
plated in the Andean Common
Market regulations, the possibility
exists under certain conditions, for
goods undergoing a process of
"re-nationalizing" in one of the
Pacta Andino countries to enter this
market under the same conditions
as those manufactured within the
economic area . The "re-nationaliz-
ing " procedures vary from a simple
transit operation where the goods
are declared to be of local manufac-
ture after paying a duty to a refilling
or repackaging process. Another
alternative is where the addition of
locally manufactured and unsophis-
ticated oarts to the imported item is
sufficient to declare it to be of local
ongin .
Barter and compensation transac-
tions-- Exports m·ay also be created
under barter or compensation
agreement. The country which may
show interest in barter usually
suffers from a shortage of foreign
exhange and the inability to dispose
of surplus goods at normal market
prices . Barter is often the only way
to purchase needed materials and
equipment . Some of the Central
American countries have favored
this kind of deal in the past in order
to dispose of their agricultural
surplus. El Salvador, Guatemala and
Nicaragua have all allowed this
system , sometimes with Eastern
European countries, and often sell
goods like coffee to non -traditional
coffee-consuming countries in ex-
change for much - needed raw -
materials.
60
This method of trading is not
limited to Central America . The
severe economic situation in coun-
tries such as Chile, Argentina and
even Brazil is opening doors to all
kinds of sophisticated commercial
combinations and deals on the
conditions that the proposition al-
lows them to increase the export
volume of locally produced goods
and to import raw materials that
they have a hard time paying for .
Argentina, for example, hitting an
all-time low of foreign exhange
reserves and unable to sell accumu -
lated stocks of meat, hides, wool,
cotton and wines, is a good
possibility and so is Brazi l which
recently made overtures to Com-
munist China to exhange crude oil
against Brazilian industrial goods .
Blocked accounts-- In a number of
countries there exists the so-called
" blocked account," normally own-
ed by non -residents and with very
limited use . These accounts are only
transferable within the country and
between non -residents, but can,
under certain conditions, be used
for commercial deals and serve as
payment, non -transferable, cover-
ing imports from abroad . Lately,
these funds have found application
by foreign travel agencies which
promoted tourism to countries
where local expenses like food and
hotel accomodation have been paid
from blocked accounts .
All of these different systems for
payment have possibilities for the
would-be amusement machine ex-
porter to Latin America , although
each has only a degree of applica -
tion .
and see if they are filled up with
solder. Any hole that is not filled up
must be suspect. Use a soldering
iron with a fine point and heat up
the plated -thru hole . Sometimes
heating up the hole will " blow
open " the hole and produce a hard
failure . If this doesn 't work , all of
the plated -thru holes in the suspect-
ed area will have to be repaired .
I have found that repairing four to
six plated-thru holes at a time and
checking the results is a good
method . It is just possible that you
may wind up repairing every plated -
thru hole in that section of the
printed circuit board .
There is only one way to repair a
plated -thru hole . Heat up the hole
and place a wire in it and solder the
wire to the printed circuit pad on
both sides of the board . Adding
solder to the plated-thru hole will
not repair the hole . The problem is
that the plated -thru hole has little or
no plating material from one side of
the printed circuit board to the
other. No amount of solder added
to the hole is going to make this
connection . Also , a gas is formed in
the hole when heat is applied to it.
This gas forces the solder away
from the center of the printed circuit
board and will prevent solder from
flowing from one side of th e PC
board to the other.
"Cold solder joints" can also
cause intermittent thermal failures .
Actually , a c old soder joint is
nothing but a bad solder joint.
When solder is applied without
sufficient heat, the solder builds up
around the leads being soldered , but
does not bond the metals together .
The result is the same as if you
twisted two wires together and
formed a mechanical joint.
As the poor solder joint cools off,
the metal contracts and the electri-
cal connection is broken. Since
cooling off the poor solder joint will
make it fail , the same troubleshoot-
ing technique used to locate thermal
failures can be used to locate a bad
solder connection .
First isolate the circuit which can
cause the problem . Then using a
can of spray coolant, spray the
solder joints in the suspected circuit .
Spray two or three solder joints at a
time . If this doesn't bring out the
fault, then resolder all the solder
connections in the trouble area . You
may never know which solder-joint
tt was , but at least you ' ll have
repaired the fault.