HP 8340b User Manual

2.
Press
[INSTR PRESET]
and
check for the following
sweep
indications:
a.
Check front
panel
SWEEP
LED.
The
LED
should
be
blinking.
The
sweep
LED,
which
is
turned
on at
start
of
sweep,
off
at
each
bandcross,
and at
end-of-
sweep,
is
controlled
by LSPLD
(low
sweep
LED).
The
sweep
LED
is
turned on when
HSP
(high
start
sweep)
is
low,
LRSP
(low
reset sweep)
is
high,
and
LBX
(low
bandcross)
is high.
b.
Check the
SWEEP OUT
signal.
The
sweep
outputs
come
from
the
A57
marker/bandcross
assembly,
and
are
generated from
the
MKR
RMP.
For
a
detailed
description
of
the
SWEEP
OUT
or
MKR RAMP
waveform,
refer
to
the
sweep
generator/YO
loop
functional
group.
If
the
sweep
out waveform
is
normal,
the
ASS
assembly
ramp
generator
is
good,
the WSPTM
(write
sweep
time)
strobe
is
generated,
and
LRESET
(low
reset)
is
working.
c.
Check
rear
panel
O.SV/QHz
waveform.
The
0.5V/GHz
signal
comes
from
the
A28
SYTM
driver
assembly,
and
is
generated
by
the
PRETUNE
signal,
which
is
generated from
VSWP.
If
the
rear
panel
O.SV/GHz
signal
is
normal,
VSWP
and
PRETUNE
are
working.
NOTE:
For
sweep
widths
<5
MHz
(20/30
sweeps),
0.5V/GHZ
is
fixed.
SPECTRAL PURITY
/
HARMONICS
(17,18)
NOTE:
In
this
section,
spectral
purity
is
considered
a
phase noise
problem
and
spurious
responses
are
considered to
be
discrete
harmonics.
Phase Noise
This
procedure
assumes
the
instrument
Failed
the
Single
Sideband
Phase
Noise
test,
in
Section
IV.
1.
If
the
instrument
failed
the
test at
offset
frequencies
less
than
300
Hz,
the
problem
is
most
likely
the
100
MHz
Reference
section.
Refer
to the
reference
loop
-
M/N
loop.
a.
Replace
the
400
MHz
input
to
A31
M/N
phase detector
(J1)
using
a
very
stable
source.
Use
the
HP
8662A
frequency
standard
as
the
HP
8340B/41B
frequency
standard
EXT
input.
b.
Repeat
the
failed
test.
If
the
HP
8340B/41B
now passes
the
test,
the
problem
is in
the
HP
8340B/41B
reference
loop.
2.
If
the
instrument
failed
the
phase
noise test
at
offset
Frequencies
from
300
Hz
to
50
kHz,
the
problem
is
most
likely
the
M/N
loop.
a.
You
can use
an
external
source
to
replace
the M/N
input
to the
YO
loop,
but
the
external
source
phase
noise
would
have
to
be much
better
than
the
HP
8340B/41B
phase
noise
to
eliminate
the YO
Loop.
b.
Replace
the
reference
loop
400
MHz input to
the M/N
loop
as
described
in
step
1.
HP 8340B/41B
Assembly-Level
Service Overall
Instrument
Troubleshooting
A-45

HP 8340b Specifications

General

Brand	HP
Model	8340b
Category	Inverter
Language	English