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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