Sweep Generator Assembly-Level Troubleshooting; Sweep Generator Assembly-Level Troubleshooting; Introduction; No Sweep - HP 8340B Manual

Sweep Generator
Assembly-Level Troubleshooting
INTRODUCTION
There are two basic failure
modes that have to do
with the
sweep
function of the instrument.
•
The
instrument
is
not sweeping.
•
The
instrument
is
sweeping,
but the sweep is
incorrect
—
the
frequency
limits of the
sweep
are
wrong and/or bandcrossings are not occurring.
The
first task is to get the instrument to
do repetitive sweeps of any
kind.
If the MARKER
RAMP (ASS TP4)
is
sweeping zero to ten volts and the front panel sweep LED is
blinking, the
instrument
is
considered to be sweeping even though the output frequency may
not be
moving.
If, on the
other hand,
MARKER RAMP
is
stuck and the front panel sweep LED
is
continuously
on or off,
the instrument is
not considered to be sweeping.
When
looking at the
LED, care must be
taken because in fast sweeps
it may appear to be
on
all
the time, even though
it
Is actually blinking.
NO SWEEP
Assuming that the instrument processor is
functioning correctly, the only
external
lines that
can
prevent
the ASS
sweep generator
from sweeping are
HSP (high sweep, A58P1-13), LBX (low band-
cross,
A58TP6)
and
LRSP (low reset sweep, A58TP11). HSP
and
LRSP
are standard
TTL
lines with
HSP
being driven by the A57
marker/bandcross assembly
and LRSP being driven
by
the A59 digital
interface assembly.
LBX
is
an
open collector
line
that
can
be driven by
both
the
ASS
sweep generator
and
A57 marker/bandcross boards. HSP
is coupled to
LBX
on the
A57 marker/bandcross assembly
so
that if
LBX
is pulled down,
the A57 marker/bandcross
assembly
pulls
down
on
HSP also.
If
the instrument
is in
the continuous sweep mode and
is
not
sweeping, remove the A57 marker/
bandcross assembly.
If
the instrument
now sweeps,
the problem is
most
likely on the A57 marker/
bandcross assembly (in the controller section). Note that
in this
mode,
the
frequency
limits that
the
instrument
is
sweeping over
will not be correct. This
is
because
it is
the
A58 sweep generator that is
pulling LBX low
to stop
the
sweep when the MARKER RAMP reaches 12 volts.
If
the instrument still will
not sweep with the A57 marker/bandcross assembly removed, place the A58
assembly on an extender
board and check the state of the
HSP
line,
A58P1-13. Since
only the A57
marker/bandcross assembly
can pull
down
on this
line, it
should be high
in
this
mode.
If it is
low,
troubleshoot this problem.
If
HSP
is
high,
check the state of LBX (A585TP6).
If it is
low,
determine
what is
pulling it low by looking at
HBX (A58TP5). If HBX
is high, the
A58 sweep
generator is faulty,
and is
pulling
down on LBX.
If HBX
is
low, troubleshoot the A59 digital interface (in the
Controller
Section).
Finally,
look at LRSP, A58TP11.
If it is
stuck low, check
it
at
its
source
—
the
A59
digital
interface
assembly.
If the three lines Just discussed, LBX, HSP and LRSP are all high,
the problem is indeed
on
the sweep
generator
assembly.
Reinstall the marker/bandcross assembly. Replace the
A58 sweep generator
assembly
or consult the A58 troubleshooting section
in
the optional Component
Level
Service Manual
set
if
component
level
repair
is
intended.
D-24
Sweep Generator Assembly-Level Troubleshooting
HP 8340B/41B