Model 8340A - Service
SWEEP GENERATOR - YO LOOP
TROUBLESHOOTING TO ASSEMBLY LEVEL
YO LOOP TROUBLESHOOTING
Introduction
The YO UNLOCKED error condition can be caused by a number of
different failure mechanisms. The YO Loop Troubleshooting Flow
Chart, Figure 8D-2a, provides a systematic way to identify the
board or boards at fault for the majority of the cases. Refer
also to the sweep Generator and YO Loop Block Diagram, Figure
8D-l. Each of the following headings refer to the Troubleshooting
Flow Chart and assumes that the Front Panel UNLK indicator is
lit.
YO UNLK - CW/MANUAL Mode
The instrument UNLK diagnostics can be selected by pressing
[SHIFT]
[EXT]
on the front panel. This will display the
following:
OSC: REF M/N HET YO N2 Nl
A YO unlock condition exists when the "YO" indicator is flashing.
In the majority of 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 acquire phase-lock in
CW/MANUAL at all frequencies, then it wil� also not function
properly in the SWEPT mode.
To troubleshoot in the CW/MANUAL mode, answer the following
questions:
(1)
ARE OTHER LOOPS LOCKED?
Check to see that the UNLK indicators for the REF, M/N, N2, and
Nl loops are not also flashing. If these other loops are
unlocked, then the YO Loop will not function correctly;
troubleshoot the other loops first. If they are all locked, then
proceed to question 2.
(2)
IS FRONT PANEL RF POWER OK?
Check that RF is present at the front panel at a level close �o
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
8-289
Scans by HB9HCA and HB9FSX
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