Fluke 6060B - AM Troubleshooting; Internal;External am

MAINTENANCE
TROUBLESHOOTING
AND
REPAIR
voltage here should
be
approximately 1 .6V dc.
With
the RF off, the voltage
at TP7 should
be
OV
dc.
When the problem
is isolated
to a specific area,
use the schematic. Theory
of Operation,
Test Point Chart, and
normal
troubleshooting
techniques
to isolate the
fault.
4D-45. AM
TROUBLESHOOTING
The following
paragraphs
provide information
that help the
operator to trace an AM
problem to a specific
circuit on the Output
assembly.
4D-46.
Intemal/External
AM
If
an AM problem exists, determine
if the problem
occurs
with internal AM,
external AM
or
both. This
check is done by
connecting
a 1
V
peak (2V
p-p),
1-kHz signal
source to the
external MOD INPUT
of
the
UUT and
measuring
AM depth.
Use a ^Modulation
Analyzer.
Program
the UUT to external
AM
and then to
internal
AM at UkHz internal
modulation
rate. The measured AM
should agree with
the programmed depth
within a
few percent.
Tables 4D-17 and
4D-18 provide control
information
for
modulation
and modulation
frequency selection.
If the internal AM does
not
agree, but external
AM is Ok, the
Modulation
Oscillator is
likely at fault. If external
AM is bad,
but internal
AM is
Ok, then
the problem is
somewhere
between the external
MOD
INPUT and
the AM DAC.
If both the external
and internal AM fail,
the problem
is
likely being
caused
by cither the
modulation
signal-processing
circuit
or the leveling
loop. To determine
which circuit
is
faulty,
perform
the following test.
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II
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Table
4D-17.
Modulation ON/OFF Control
INT
AM EXT AM
INTAML
EXTAML
Off Off
1
1
Off On
1
0
On
Off
0 1
On
On
0 0
INT
FM
EXT FM
INTFML EXTFML
FMENH
Off
Off
1 1
0
Off
On
1
0 1
On
Off
0
1 1
On On
0 0 1
1
=
TTL High
0
=
TTL Low
Table 4D-18.
Modulation
Frequency
Control
FREQUENCY
MF400L
400 Hz
0
1 kHz
1
1
=
TTL
High
0
=
TTL Low
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4D-20