After
Service
Product
Safety
Checks
W
arning
Whenever
it
appears
likely
that
protective
safety
provisions
have
been
impaired,
the
apparatus
shall
be
marked
as
inoperative
and
should
be
secured
against
any
unintended
operation.
The
protection
provisions
will
have
likely
been
compromised
if,
for
example:
The
instrument
shows
visible
signs
of
damage
.
The
instrument
fails
to
perform
the
intended
measurement.
The
unit
has
undergone
prolonged
storage
under
unfavorable
conditions
.
The
instrument
was
severely
stressed
in
transport.
P
erform
the
following
ve
safety
checks
to
verify
the
safety
condition
of
the
4338B
(these
checks
may
also
be
used
for
safety
checks
after
troubleshooting
and
repair).
1.
Visually
inspect
the
interior
of
the
instrument
for
any
signs
of
abnormal
internally
generated
heat,
such
as
discolored
printed
circuit
boards
and
components
,
damaged
insulation,
or
evidence
of
arcing.
Determine
the
cause
,
and
repair
.
2.
Use
an
ohmmeter
which
can
accurately
measure
0.1
to
check
the
resistance
from
the
instrument
enclosure
to
the
power
cord's
ground
pin.
The
resistance
must
be
less
than
0.1
.
Flex
the
power
cord
while
making
this
measurement
to
determine
if
any
intermittent
discontinuities
exist.
3.
Unplug
the
4338B's
power
plug
from
the
power
source
.
Set
the
line
switch
to
ON.
Tie
the
line
and
neutral
pins
of
the
power
connector
together
and
check
the
resistance
between
them
and
enclosure
.
The
minimum
acceptable
resistance
is
5
M.
Find
and
replace
any
component
which
causes
the
instrument
to
fail
this
test.
4.
V
erify
that
the
correct
fuse
is
installed.
5.
V
erify
that
the
grounding
wire
(green
and
yellow)
is
secured
to
the
chassis
by
a
screw
and
washer
.
4-2
T
roubleshooting
