Heathkit SW-7800 - Precautions for Troubleshooting

Page
112
Heathki
A
review
of
the “Circuit
Description”
may
also
help
to
determine
where
the
trouble
is
If
you
still
have
not
located
the
trouble
after
you
complete
the
“Visual
Checks,”
and
a
voltmeter
is
available,
check voltage
readings
against
those
shown
on
the
Schematic.
Read “Precautions
for
Troubleshooting”
before
you
make
any
measure-
ments.
NOTE:
All
voltage
readings
were
taken
with
a
high-input
impedance
voltmeter.
DC
voltages
and
resistances
may
vary
as
much
as
+
20%
PRECAUTIONS
FOR
TROUBLESHOOTING
Be
sure
you
do
not
short
any
terminals
to
ground
when
you
make
voltage
measurements.
If
the
probe
should
slip,
for
example,
and
short
across
compo
nents
or
voltage
sources,
it
is
very
likely
to
cause
damage
to
one
or
more
components
NOTE:
In
the
unusual
event
where
you
are
unable
to
resolve
a
difficulty,
refer
to
the
“Customer
Se
vice”
information
inside
the
rear
cover
of
this
Man
ual.
Your
Warranty
is
located
inside
the
front
cover,
TROUBLESHOOTING
CHARTS
‘The
following
charts
list
the
condition
and
the
possi-
ble
causes
of
several
malfunctions.
If
a
particular
part
is
mentioned
as
a
possible
cause,
check
that
part
to
see
if
it
was
correctly
installed.
Also
check
GENERAL
the
parts
connected
to
it
for
poor
connections.
Itif
also
possible,
on
rare
occasions,
for
a
part
to
be
faulty
and
require
replacement.
CONDITION
POSSIBLE
CAUSE
Receiver dead.
F1
(F401
ifexternal
DC
power
is
used)
Sw.
m1
(0426
through
428,
No
sound
from
the
speaker.
rr
sP1
uss,
Shielded
cabies
to
RS
or
SW2.
Audio
hiss,
but
no
signals.
Antenna,
Udo,
Udo2,
401
D401
through
D413.
‘See
“Controller”
and/or
“Synthesizer”
troubleshooting
charts)
*;
No
signals
in
the
AM-NAR,
USB,
or
LSB
modes.
AM-WIDE
Is
okay’