Overall Assembly-Level Troubleshooting; Overall Assembly-Level Troubleshooting; Troubleshooting Sequence - HP 8340B Manual

RF Section
Overall Assembly-Level Troubleshooting
Begin initial instrument troubleshooting
in
the service introduction section. Once you
isolate the prob¬
lem to the
RF
section, the troubleshooting in
this
section can be broken into three areas:
•
SYTM
peaking
Peaking
is
a
function designed to tune the
SYTM so that the RF output is in
the center of the
SYTM
passband, ensuring that maximum RF power
is available. Use the
SHIFT MANUAL sweep
diag¬
nostic to troubleshoot the peaking function.
•
ALC
loop
The
ALC loop
is
a
feedback
control system
that monitors RF power
and maintains that
power
at
a
set level.
A voltage representing the RF power
level
is
detected (internally or externally) and
compared to
a
reference
level.
If
the levels are
unbalanced, the ALC
circuitry drives the modu¬
lators and varies the RF output
until the voltage
levels balance.
Use the
SHIFT METER
diagnostic
to open the ALC loop for troubleshooting.
•
RF path
The RF path consists of 14 RF microcircuits and their associated bias assemblies.
To
trou¬
bleshoot the RF
path, initialize the instrument to
a
known state and measure the RF power levels
at various junctions in the path. Minimum power levels are provided for each microcircuit on the
RF
path troubleshooting block diagram.
TROUBLESHOOTING SEQUENCE
Troubleshoot the RF
section
in an ordered sequence to systematically isolate assemblies:
1.
SYTM
peaking problems
2.
ALC loop problems
3.
RF path
problems
Each troubleshooting sequence leads to the next. What may
appear
to be an
ALC loop fault, for
example, may
actually be an RF path (microcircuit) failure. By completing the ALC loop diagnostics,
the RF path
failure is
indicated, leading you to
the
RF
path troubleshooting procedures.
HP 8340B/41B
RF
Section
Overall Assembly-Level Troubleshooting H-15/H-16