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In
general,
start
troubleshooting with
Table
5-3,
line
power
checks,
to
verify
that
the
power
supplies are providing
the
correct voltages
to
the
electronic
components.
5.6.3
Battery
Power
If
trouble
occurs
on
battery
power
only,
or
if
battery
operating time
is
substantially less
than
six
hours
after
over-
night charging,
test
the
batteries
and
charging
circuit
per
Table
5-4.
5.6.4
Display
and
A/D
Converter
Proper
operation
of
the
A/D
converter
and
display
should
be
verified
before troubleshooting the
signal
conditioning
cir-
cuits.
Check
the
A/D
converter
and
display per
Table
5-5
and
5-6, respectively.
5.6.5
AC
Converter
Problems
with
AC
voltage or
AC
current
ranges
may
involve
the
AC
converter.
Check
this circuit
per Table
5-7.
If
the
pro-
blem
is
only
on
AC
current ranges,
see below.
5.6.6
Chopper
Amplifier
and
Ohms
Source
Problems
with
DC
voltage,
DC
current, or resistance
ranges
may
involve the
chopper
amplifier.
Check
this circuit
per
Table
5-8.
After
verifying
chopper
amplifier
operation
by
completing
steps
1
through
10
of
Table
5-8,
go
to
Table
5-9
if
resistance
measurements
are
erratic.
If
problem
is
only
on
DC
current ranges, see below.
NOTE
Dust,
flux
or
other
contamination
will
degrade
performance
on
resistance
and
DC
voltage
ranges.
5.6.7
Current
Shunts
If
problems
occur with
current readings,
check
the
current
shunts
and
related circuitry
per Table
5-10.
It
should
be noted
that,
since the current
shunts
are
common
to
both
AC
and
DC
current,
problems should
exist
on
the
same
AC
and
DC
current
ranges
if
there
Is
a
fault
In
the current
shunt
circuitry.
NOTE
All
measurements
are
referenced
to
analog
com-
mon
{ground
clip),
unless otherwise
noted
in
the
Tables.
If
a gross
failure
exists
that indicates a possible
blown
fuse
{line
power,
battery
pack, or current
fuse)
refer
to
paragraph
5.8
for
fuse replacement
instructions.
Some
procedures
in
the following tables
re-
quire
the use
of
high voltage.
Take
care to
prevent contact with
live
circuits
which
could
cause
electrical
shock
resulting
in
in-
jury or
death.
The
front
panel
ZERO
knob
will
have
to
be
removed
If
either
the
front
panel
or display
Is
to
be removed.
To
remove
the
knob,
proceed
as
follows;
1
.
Carefully
remove
the
end-cap
{shown
In
Figure
5-3)
using
a
thin-biaded instrument.
2.
Loosen
the
slotted
screw and
remove
the
knob from
the
shaft.
3.
Take
care not
to
damage
or lose
either
the
end-cap
or
knob.
These
items provide
protection against
electrical
shock
and must
be
installed
when
the instrument input
is
floating.
NOTE
If
the
display
board has
to
be
removed
for
troubleshooting
or
repair,
the
front
pane!
ZERO
knob
will
also
have
to
be removed.
Comparator waveform
(Logic
1
during
ramping)
+
5
I
—
0
1
1
Figure
5-2.
Integrator
and Comparator
Waveforms
WARNING
The
ZERO
potentiometer
shaft
is
electrical-
ly
connected
to
INPUT
LO. Maintain
INPUT
LO
at
ground
potential
while the
ZERO
knob
or
its
cap
is
removed
to
prevent an
electrical
shock
hazard.
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