Yo Loop Assembly-Level Troubleshooting; Yo Loop Assembly-Level Troubleshooting; Introduction - HP 8340B Manual

YO Loop
Assembly-Level Troubleshooting
INTRODUCTION
The
YO UNLOCKED
error condition can be caused by
a
number of different failures. Figure D-5, YO
Loop Troubleshooting Flow Chart, provides
a
systematic way to identify the malfunctioning assembly.
Also refer to Figure D-4,
Sweep Generator and
YO
Loop Simplified Block Diagram.
Each of the
following
headings refer to the
Troubleshooting Flow Chart and assumes that the front panel UNLK
indicator is
on.
Power levels are shown on Figure D-6.
Sweep Generator and YO Loop Troubleshooting Block
Dia¬
gram.
YO UNLK
-
CW/MANUAL MODE
NOTE:
The
[SHIFT] [M4]
diagnostic can help isolate the cause of an
UNLK condition. Use this
diagnostic
feature after performing the troubleshooting procedure shown below. Refer to the overall
instrument troubleshooting section in the service introduction for details.The instrument
UNLK diag¬
nostics can be selected by pressing
[SHIFT] [EXT] on the front panel. This will display the following:
OSC: REF
M/N HET YO N2 N1
A YO unlock
condition exists when the
"YO"
indicator
is
flashing.
In most cases,
the error condition will
occur
in the
CW/MANUAL
mode, and the troubleshooting
should be done
in this
mode
first. If the YO loop
will not phase-lock
in
CW/MANUAL
at
all
frequencies,
it will not function properly in the
SWEPT
mode.
To troubleshoot in the
CW/MANUAL mode, perform the following steps.
Refer
to Figure D-5:
1.
Are Other Loops Locked?
Check
to
see
that the UNLK indicators for the REF,
M/N, N2, and
N1
loops are
not
flashing.
If
these other
loops
are
unlocked, the
YO
loop will not function correctly. Troubleshoot the other
loops
first.
If
they
are
all
locked, proceed to question 2.
2.
Is
Front Panel RF Power Correct?
Check that RF
is
present at the front panel at
a
level close
to the selected
power.
If
not,
there
is
a
problem
in
the RF path
—
go to question
14.
If
the front panel
RF
is present at the correct power,
proceed to question 3.
HP 8340B/41B
YO
Loop
Assembly-Level Troubleshooting D-15