Reference Loop Assembly-Level Troubleshooting; Reference Loop Assembly-Level Troubleshooting; Diagram - HP 8340B Manual
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Reference
Loop
Assembly-Level Troubleshooting
The following troubleshooting procedure provides information
for isolating
a
reference loop failure to
the assembly level.
The assemblies
which are covered
in
this procedure are:
•
A29 reference phase detector
•
A30
100
MHz VCXO
•
A34 reference
loop
—
M/N
loop
motherboard
•
ASS digital interface assembly.
During troubleshooting, refer to Figure B-21, Reference 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 reference loop
output
signals (Figures
B-2 through
B-11).
NOTE:
In
the following procedure,
the
acronym
DUT
(device under test)
is
used to
describe the
instrument you are troubleshooting.
1.
Ensure that the rear panel
INT/EXT FREQUENCY STANDARD
switch
is
in
the
INT
position and
that
a
BNC cable
is
connected between
the INT and
EXT BNCs (the front panel's EXT REF
annunciator should be
off).
If
the instrument had been connected to
an
external frequency standard and the
REFERENCE
UNLOCK
condition now
goes away, the problem
is
with the external frequency standard.
2.
Disconnect the
BNC cable from
the rear panel
INT BNC
and verify that
there
is
a
10
MHz,
>
0
dBm
signal present.
If
this signal
is
not
present or
is
low
in
power, go to step 3.
If
the frequency
is
incorrect, perform the 10
MHz
frequency standard adjustment
in
Section
V
of
the Calibration Manual before troubleshooting further.
If
the signal level
and frequency are good, reconnect the BNC jumper cable
and
go
to
step
5.
3.
Remove the YO Loop from
the instrument (the
YO
Loop disassembly procedure
is
provided
in
the
Sweep Generator
—
YO Loop
functional group).
Disconnect A51W1 from the main motherboard
connector A62J3
and
measure
the
voltages at A62J3 pins
1
and
5
(refer to Figure B-12).
If
the
proper voltages are
not present, troubleshoot the
power supplies.
If
the voltages
are present,
proceed with step 4.
4.
Remove
A51
and reconnect A51W1 to A62J3.
Measure
the frequency and power directly out of
A51.
If
the signal
is
not
present or
incorrect,
replace A51.
If
the signal
is
good, replace J9W1.
5.
Disconnect J10W10 from A29J1 and measure the
signal directly
out of J10W10.
The
signal should
look identical to the one measured
in
step
2.
If
the signal
is
not present, there
is
a
problem
with
either the
rear panel BNC jumper cable
or J10W10.
If
the signal
is
good, reconnect J10W10 to
A29J1 and
proceed
with
step
6.
6.
Measure
the voltage at TP1,
TUNE, on the
top cover of the A30 assembly. This test point should
be
approximately —8V when
the
reference loop
is
locked (TP1
is
approximately —1V or approx¬
imately —25V when the reference loop
is
unlocked).
If
the voltage at
TP1
is
not —8V, proceed with
step 7.
If
the
voltage
is
—8V, proceed
with
step
13.
HP 8340B/41B
Reference Loop Assembly-Level Troubleshooting
B-9
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