Yo Unlk Swept Mode - HP 8340B Manual

16. Is
the YO Main Coil Drive Correct?
Check the YO MAIN COIL DRIVE. This
can be done
by testing the
SENSE voltage, TP4 on the ASS
YO driver assembly. (The SENSE
voltage is related to the
YO frequency by
-2.4
V/GHz.)
If
the
YO
main coil is greatly mistuned, no
YO
signal will be present.
If
the
SENSE voltage (hence the YO
MAIN COIL DRIVE current)
is
correct to within
±1V,
troubleshoot the YO;
if
not,
proceed
to
question
17.
17. Is
the PRETUNE Voltage Correct?
This portion of the troubleshooting
guide
is
a
branch from question 3, question
10,
and question
16.
Check the
PRETUNE
voltage.
PRETUNE
has
a
sensitivity
of
-2.5
V/GHz of YO frequency.
If
the
PRETUNE
voltage is
correct, troubleshoot the
ASS
YO driver (OFFSET
and
GAIN)
and the
A47
sense resistor assembly.
If
PRETUNE
is not correct, proceed to question
18.
18. Is
the VSWP Voltage Correct?
Check that the
VSWP
voltage
is
zero
volts.
If it is
correct, suspect the AS4
YO pretune/delay
compensation assembly.
If VSWP
is
much different than
zero volts,
proceed to question
19.
19.
Is LVSX Low?
If
the
VSWP
voltage
is much different than zero
volts,
it will affect the PRETUNE
voltage only
if
the
AS4 YO
pretune/delay compensation assembly
is
also not operating correctly. If LVSX (low
volt¬
age sweep
disable)
is
high or intermittent, troubleshoot the ASS digital interface
assembly
(in the
controller section).
If
LVSX
is
low (that should be the case for
CW/MANUAL), the trouble
is in
the
AS4
YO pretune/delay compensation assembly.
In either case, also troubleshoot
VSWP
on the
ASS
sweep generator assembly.
YO UNLK
-
SWEPT MODE
To troubleshoot in the
swept mode with the YO unlocked, perform the following steps:
1.
Is
CW/MANUAL Mode Correct?
If the YO UNLK error condition can
be made to
occur
in
the
CW/MANUAL mode, go to the YO
UNLK
-
CW/MANUAL
troubleshooting section.
It will
also
be helpful if
the
YO UNLK
condition
can be made to occur in
the SINGLE SWEEP mode,
for
this will hold the YO loop (error) condition
constant while troubleshooting.
If
the error condition can only be
made to
occur
In
the
SWEPT
mode and
CONTINUOUS SWEEP
mode, the problem will be more difficult to
solve. Proceed to question
2
in
this section.
There are
several malfunctions that could cause
a
YO loop unlock
in
only the swept mode
—
these relate to
the function and operation of VSWP,
LKICK, HLEY (high lock enable YIG
oscillator), and possibly
VCOMP, LVSX, and LYSP. Most of the potential causes of the error are related
to timing, mainly at
the start of sweep.
D-18
YO
Loop Assembly-Level Troubleshooting
HP 8340B/41B