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Section VIII
SERVICE
GROUP
B
Model 3455A
d.
To
determine which
cal
constant
is
measured, connect a
high
input
impedance
DVM
(10
V
range
input
impedance
>
IO>o
ohms)
to
one
of
the points
shown
in
Table
8-B-5.
e.
By
stepping
through
the
cal
constants
from
constant
13
to
0
and
monitoring
one
of
the
points
in
Table
8-B-S,
every
cal
constant
step
can be
located.
NOTE
The
voltages
listed in
Table 8-B-5
are
approximate
and
should
only
be used
to locate
Auto-Cal
constants
and
for
troubleshooting.
8-B-13.
By
using
the
cal
constants stepping
procedure
in
conjunction with Table
8-B-5,
any
one
constant step
can be
located.
When
using
this
method
and
the
345SA
is
malfunctioning,
or
possibly
two
conditions
in
Table
8-B-4
may
be
inoperative.
(Example; Readings
at
A10TP4
and
TP2
are bad).
It
is
very
unlikely,
however,
that
all
four conditions
are
in-
operative.
If this
should
occur, then
check
the
+
10
V
reference
and/or
the
inguard
logics.
Table 8-B
S.
Cal
Constant Monitoring
Points.
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Approximate
A
1
0TP4
Voltage
Voltage
at
the Multiplexer
Mode
(Source
of
A10QY)
Voltage
at
the
Junction
of
A10K6
and
A10R47
A10TP2
Voltage
0 0
0
10
0
0
0
6
-10
0
0
0
0
10
-
-
-
10
-----
-
-
-
-9.9009
-
® ®
-
8 B-14.
Switch
Closure
Table.
8-B-15.
Most
of
the
switch closures
used
in
the
345SA
are
listed in
Table
8-B-6.
This
table
lists
the
previous
closures
dependent
on
the range, function,
and Auto-Cal
mode
of
the
34SSA. For
troubleshooting malfunctions
of
the various operations
of
the instrument,
this
table
may
be very
helpful.
8 B-16. Auto-Cal Troubleshooting (Schamatie
1, 7).
8-B-17.
Most Auto-Cal
failures
also
show up
as
dc
failures
and
should be
repaired
first.
These
malfunctions
usually
show up
as a
failure
in
the
self-test
mode
of
the
345SA.
The
following are a cou-
ple
of
hints to
troubleshoot
these
malfunctions.
a.
Set the
3455A
to the
self-test
mode
and
find
out
which
cal
constants are
failing.
Take
the
3455A
out
of
the
self-test
mode
(press
any
other function button).
Using
the
cal
constants
service
procedure,
go
to the
bad
cal
constant.
While
refering to the
various
tables
and
figures
in this
service
group,
troubleshoot the
bad
constant.
8-52
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