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Section
V
replaced,
the
component
selection procedure
must
be
repeat
ed. This procedure
requires
extensive
tests using
a
temperature controlled
chamber and widely varying
tem-
peratures. Fo
r
this reason,
the Amplifier Assembly
A2
should
be returned
to
the factory if any
of
these
critical
components
must
be
replaced.
The
critical
parts are
shown
in the
shaded areas of
the
component
location
drawing
in
Figure
7-3.
5-33.
A
factory
rebuilt
and
tested assembly,
-hp- Part
No.
03482-69502,
may
be
purchased
on
an exchange basis.
The
-hp- Part
No.
of a
new assembly
is 03482-66502. Contact
your nearest
-hp-
Sales
and
Service Office, listed
in
Appendix
B,
for
exchange details
and
prices.
5-34.
TROUBLESHOOTING.
If
the
Model
3484A
operates incorrectly and the trouble
cannot be
corrected by the Adjustment
Procedures,
Para-
graph
5-13, the following
troubleshooting information
should
be used
to locate the source
of trouble. The
troubleshooting procedures
will help
determine
if the
t rouble is in
the
3484A
or the
3480A/
B.
Also c heck for
loose wires
or
other
obvious evidence of trouble,
such
as
loose or
burned components.
Make
sure that
printed
circuit
boards
are
seated properly in
connectors.
In
general,
the
troubleshooting
information
is
identified
by
assembly
and
according to
the
symptoms experienced.
BEFORE WORKING
WITHI
N
THE
3484A,
REFER
TO
PARAGR
APH
5-24,
CLEAN
HANDLING
TECHNIQUES.
DI RT OR
CONTAMINATION IN
THE
INTERIOR
OF
THE
3484A MAY
DE-
G RADE PERFORMANCE.
5-35.
DC AMPLIFIER
ZERO
OFFSET.
If
the
instrument
exhibits a zero offset t hat cannot
be
corrected
by
performing the
Amplifier
Zero
and
Offset
Current Adjustments in
Paragraph
5-16,
follow the pro-
cedure given
in
the
Zero
Offset Troubleshooting Tree,
Figure
5-12.
5-36.
DCV DISPLAY LIMITING.
Display
"limiting"
is
the
term
used
to
describe the
condition wherein the
display reads correctly
up
to
a
certain
point, but will
not read
higher. This
limiting may
occur
at the amplifier
input or
output, or
within
the
amplifier.
The
first
check in the
Limited
Display Trouble-
shooting
Tree,
Figure
5-13,
det
ermines
whether
the
trouble
is
in
the 3484A or the 3480A/B.
5-37. DC AMPLIFIER GAIN
ERRORS.
If
readings
are consistently
high
or
low
on a certain
de
range, and the trouble cannot
be
corrected
by
performing
5-10
Model
3484A
the
Adjustment Procedures in
Paragraph
5-13, information
in
the
fo llowing paragraphs
and
Table
54 should
locate
the
source of
trouble.
5-38. Attenuatio
n
is
l
/
l in
the three
lower
ranges and
I
/
I
00 in
t he
I
00
V
and
I
000
V
ranges.
If
leakage resistance
is
present across attenuator
resistors or reed contacts,
or if
attenuator relays do
not operate
properly
,
attenuation
will
not be
correct. For
example, referring to
schematic
diagram
Figure
7-3,
if Al K3
remains closed
on the
100 mV
,
1000 mV, and 10
V
ranges,
the
display will be approxi-
T
able
5-4.
DC A mplif ier
Gain Errors.
SYMPTOM
PROBABLE CAUSE
Readings
are high (or
inter·
High
resistance
connection
in relay
mittently
high) on
A2K1
1000
mV
range
only.
Connect
clip lead
across
reed
switch
of
A2K
1.
Be
careful not
to pu
t
stress on
reed
.
I
f
display is correct,
check
reed
connections.
I
f
con-
nections
are
good,
replace reed.
I
f
c
lip lead does
not
correct the
read-
ing,
trouble may be
in
A2R39.
Readings
are
high
(or
inter-
High
resistance
connection
in
relay
mittently
high)
on
10 V
A2K2.
and
1000 V
r
anges.
Connect clip
lead
across
reed
switch
of
A2K2.
Be
careful not to
put
stress
on
reed.
I
f
display
is
correct,
check
reed
connections.
I
f
con-
nections are good, replace
reed.
Readings are low on 100
mV
Leakage
resistance
across A2K
1
o
r
2.
range only
.
Disconnect
either
end of A2K2
reed
switch.
See
Paragraph
5-25
for
reed r
emoval
instructio
ns.
If
this
corrects
trouble, check
for
leakage
across reed or
from reed to
shield
or
coil.
If trouble
is
not
cor-
rec
ted, perform
same check on
A2K1.
Readings
o
n 100
mV,
Relay
A
1
K3
may remain
closed.
1000
mV
and 10 V
ranges
are approximately half
of
correct
value.
Readings
are co
rrect with
Leakage
resistance across
a fi
lter
fi lter OUT, but
are
low
capacitor
or
from filter
relay
reed
with
filter A
or B or both.
to coil or
shield.
With
an
in
put
voltage
applied, check de
vol
tages
at junctio ns
of
A 1 R6 and 7.
7 and
8, and 8
and
9.
Voltages
should be
equal
to
voltage at input end of
A 1 R6.
A
lower
voltage
at any
point
(progressing from left
to
right
on
schematic) incicates leak-
age
to
ground
at
that
point.
Low readings
on all
ranges
Leakage
resistance across
A
1
R2C
or
and in all
fi
lter
positions.
A 1
R5.
Check
A
1
K3
for leakage
fro
m reed
to
coil
or
shield.
-
.
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Table of Contents
Troubleshooting
