M/N Loop Assembly-Level Troubleshooting; M/N Loop Assembly-Level Troubleshooting; M/N Verification And Low Output Power Troubleshooting - HP 8340B Manual

M/N
Loop
Assembly-Level Troubleshooting
The following troubleshooting procedure
provides information for isolating an
M/N
loop failure to the
assembly
level.
The assemblies which are covered
in
this
procedure are:
A31 M/N
phase detector assembly
A32 M/N VCO
assembly
A33 M/N
output assembly
A34 reference loop
—
M/N
loop motherboard
A59 digital interface assembly
During troubleshooting, refer
to Figure B-21,
M/N
Loop Troubleshooting Block Diagram. When an
output signal level is not mentioned
in
the troubleshooting procedure, refer to Figure B-21 for the
required level. Also provided in this section are the spectrum analyzer
plots
of the
M/N
Loop output
signals (Figures B-13 through B-20).
M/N VERIFICATION AND LOW OUTPUT POWER TROUBLESHOOTING
NOTE: Before replacing
A31,
A32, or A33, 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. For the
A31
and
A33 assemblies,
a
missing
power
supply is due to
either
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 can also be due to
a
failure on the
A33 assembly.
This verification is
to determine
if
the
M/N
Loop outputs
the correct
M/N OUT signal
(frequency and
power
level)
over the entire range of its internal
dividers.
If
you
have already determined
a
CW
frequency that
generates an incorrect
M/N
output frequency, you
don't need
to perform
this verifica¬
tion.
Proceed to step
1
of the
M/N
Output Frequency Incorrect troubleshooting, below.
If
you are not
sure which
CW frequency causes
the incorrect
M/N OUT
signal, proceed with step
1
of the verifica¬
tion.
NOTE:
Pressing
[SHIFT] [M1]
displays, from left to right:
M
Divide
N
Divide M/N OUTput
20/30 OUTput
Number Number
Frequency (MHz) Frequency (MHz)
NOTE:
In
the following procedure, the acronym DUT (device under test)
is
used to describe the
instrument
you
are troubleshooting.
1.
Connect the frequency counter's PREQ 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).
2.
Disconnect the
SMB
cable from
A33J2
and
connect the frequency counter's
10
Hz
—
500 MHz
input to A33J2.
HP 8340B/41B M/N
Loop Assembly-Level Troubleshooting B-21