Heathkit DX-40 - Page 10

GENERAL
SERVICE
SOLDERING:
Cold
and
loose
solder
connections
are
a
common
source
of
trouble
in
assembling
any
piece
of
electronic
equipment.
Sometimes
apparently
good
solder
connections
will
have
an
insulating
coating
of
rosin
between
the
wire,
the
terminal
and
the
solder.
This
type
of
defec-
tive
soldering
is
very
difficult
to
locate
in
the
process
of
trouble-shooting,
and
the
builder
will
do
well
to
see
that
each
wire
in
a
connection
point
is
firmly
embedded
inthe
solder.
Many
times
when
more
than
one
wire
is
connected
to
a
terminal
or
lug
the
lower
wire
will
not
receive
suf-
ficient
heat
or
solder
even
though
the
connection
looks
satisfactory.
Trouble
can
also
be
caused
by
being
too
generous
with
solder
and
heat,
with
a
short
resulting
from
solder
running
down
the
lug
and
touching
the
chassis
or
other
components.
Use
extreme
care
when
soldering
to
switch
contact
points,
to
avoid
solder
running
too
far
and
spoiling
the
spring
tension
of
the
contacts.
With
miniature
tube
sockets
there
is
a
possibility
of
shorts
between
adjacent
socket
terminals
due
to
the
close
spacing.
This
should
be
checked
and
if
any
doubt
exists,
the
terminals
should
be
pried
apart
until
obvious
spacing
can
be
seen
between
them.
In
general,
do
not
rely
on
the
solder
itself
to
form
the
electrical
connection.
A
firm
metal
to
metal
contact
should
be
made
before
flowing
the
solder
over
it.
COMPONENTS:
Any
part
that
physically
looks
defective
should
be
tested
with
the
proper
in-
strument.
TUBES:
Tubes
can
be
checked
ona
tube
checker
but
the
best
method
is
by
substitution.
An
extra
set
of
tubes
should
be
on
hand
for
testing
and
to
replace
normal
tube
failures.
WIRING:
Mistakes
in
wiring
are
the
most
common
cause
of
difficulty.
Consequently,
the
first
step
is
to
recheck
all
wiring
against
the
pictorials
and
schematic
diagrams.
Often
having
a
friend
check
the
wiring
will
locate
an
error
consistently
overlooked.
Follow
the
construction
manual
and
pictorials
so
that
each
lead
is
placed
in
its
proper
position.
Make
leads
as
short
as
possible,
except
where
leads
are
measured
or
specifically
routed
around
the
edge
of
the
chassis.
This
is
toprevent
adverse
effects
such
as
spurious
RF
oscillations
and
audio
feedback.
CAUSE
AND
EFFECT:
Be
sure
to
reread
the
circuit
description
on
page
3
so
that
"cause
and
effect"
reasoning
may
be
employed
as
the
search
for
trouble
progresses.
If
some
difficulty
still
persists
after
the
steps
outlined
have
been
completed,
attempt
to
localize
the
trouble
to
a
particu-
lar
stage
in
the
transmitter
circuit.
Use
the
tuning
procedure
as
a
basis
for
localization
and
refer
to
the
block
diagram
and
schematic
to
visualize
circuit
relationships.
The
panel
meter
and
station
receiver
are
valuable
tools
to
use
in
locating
trouble.
TRACING
PROCEDURE:
For
the
following
tracing
procedures,
use
the
schematic
diagram
for
reference.
If
any
activity
is
noted
when
the
line
cord
is
plugged
in
ard
the
operation
switch
is
in
the
OFF
position
the
AC
circuit
should
be
traced.
One
side
of
the
line
cord
is
connected
through
a
line
choke
to
one
side
of
the
primary
of
the
power
transformer.
The
other
side
of
the
line
cord
is
connected
through
a
line
choke
to
the
blue
cable
wire
which
connects
toterminal
11
of
the
opera-
tion
switch;
the
black
cable
wire
returns
from
switch
terminal
12,
to
the
other
primary
side
of
the
transformer.
Contacts
11
and
12,
of
the
switch
thus
control
line
power
to
the
transformer.
Also
check
the
four
.001
yf
1400
volt
disc
ceramic
capacitors
connected
across
the
line
for
shorts.
If
the
tubes
and
pilot
light
do
not
light
up
when
the
operation
switch
is
set
to
STANDBY
position,
again
check
the
AC
circuit
with
the
line
cord
unplugged
todetermine
why
the
transformer
is
not
receiving
power.
If
the
tubes
do
light
up
withthe
power
on
and
the
meter
reads
in
PLATE
posi-
tion,
or
some
other
indication
of
high
voltage
being
applied
is
apparent,
check
the
following.
Unplug
the
line
cord,
then
with
an
ohmmeter,
check
from
#5
on
KK
to
ground.
It
should
read
Page 35