M/N Output Frequency Incorrect - HP 8340B Manual
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M/N OUTPUT FREQUENCY INCORRECT
NOTE:
Before replacing
A31,
A32, or
ASS,
remove
the assembly from the instrument and verify that
the appropriate power supply voltages are present
at the
assembly's
input.
Refer
to the end of the
Service Introduction
in
this manual
power
supply input information. For the A31 and ASS
assemblies,
a
missing power supply
will
be caused either by
a
failure on the
A34 reference
loop
—
M/N
loop
motherboard or
a
failure
in
the
power
supplies.
In
the case of A32,
a
missing power supply could also
be due to
a
failure on
A33.
1.
ON
the
DUT, press [INSTR PRESET] [CW].
Either set the
DUT
to
a
CW frequency
that causes and
incorrect
M/N
Loop output frequency (M/N OUT), or to
a
CW
frequency that causes
the front
panel
UNLK
annunciator to light.
2.
Press
[SHIFT] [EXT]. The
following phase lock loop diagnostic should be displayed
in
the ENTRY
DISPLAY:
OSC: REF
M/N
HET YO
N2
N1
If
REF
is
flashing,
troubleshoot the reference
loop.
The
reference loop must be phase-locked
before
the
M/N
loop can phase-lock.
3.
Connect the frequency counter's FREQ STD
OUT
to the DUT's rear panel EXT FREQUENCY
STANDARD
input. Switch
the DUT's
FREQUENCY STANDARD
switch to the
EXT
position (the
EXT REF annunciator should
be on).
4.
Verify that the output frequency from A29J2
is
20
MHz
±2
Hz and that
its
output power
is 0
dBm
±3
dB.
If
the signal's frequency or power
level
is
incorrect, troubleshoot the
reference
loop.
5.
Verify that the output
frequency
from A30W1
is
400 MHz
±2
Hz
and that
its
output power
is
approximately —10 dBm
±3dB.
If
the signal's frequency or power
Is
incorrect troubleshoot
the
reference
loop.
6.
On the DUT, press
[SHIFT] [M1]. The DUT
will
display, from left to
right,
the following information:
M
Divide
N
Divide
M/N OUTput
20/30 OUTput
Number
Number
Frequency (MHz)
Frequency (MHz)
Verify that the signal out of
A33J2
is
at the displayed
M/N
output frequency
±2
Hz
and that
its
power
level
is
3
dBm
±3
dB.
If
the output frequency
is
incorrect,
proceed
to
step
7.
If
the output
frequency
is
correct but the output
power
is
low,
perform the
M/N
Divider Verification and Low
Output
Power
Troubleshooting above.
7.
Remove the
SMB
cable,
A31W2,
from A33J1 and
install an
SMB
tee onto A31W2. Connect
the
second
port of
the
tee
to A33J1 (you
will
need to use an
SMB
Jumper
cable) and connect
the third
port
to the
frequency counter's
10 Hz
—
500
MHz
input.
8.
Multiply the displayed
M/N
output frequency by two and verify that the counter indicates
this
frequency
±2
Hz.
If
the output
frequency
is
correct, replace A33.
If
the
frequency
is
incorrect,
proceed to step
9.
9.
Switch the
DUT
to STANDBY. Remove the
A31
assembly from the instrument and
place
it
on
an
extender board. Switch the DUT ON. The
M
and
N
divide numbers should
still
be
displayed
in
the
POWER dBm
display.
HP 8340B/41B
M/N
Loop
Assembly-Level Troubleshooting
B-23
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