HP 8340b User Manual

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

HP 8340b Specifications

General

Brand	HP
Model	8340b
Category	Inverter
Language	English