TM 9-4935-601-14-7&P
Model 8640B
SECTION VIII
SERVICE
8-1. INTRODUCTION
8-2. This section provides instructions for
troubleshooting and repairing the Hewlett-Packard
Model 8640B Signal Generator.
8-3. Principles of operation and troubleshooting
information are located opposite the schematics on the
foldout Service Sheets. The last foldout in this manual
has top and bottom internal views of the instrument
showing the locations of the major assemblies and some
of the chassis parts. The next-to-last foldout has top
and bottom internal views with the covers removed from
the castings; these views show the locations of the sub-
assemblies, the adjustments, and most of the
instrument's test points.
8-4. The rest of this section has general service
information that should help you to quickly service and
repair the Signal Generator.
8-5. PRINCIPLES OF OPERATION
8-6. Principles of operation appear on the foldout
pages opposite the block diagrams and the schematics
on the Service Sheets. Service Sheet 1 is an overall
block diagram that briefly describes overall instrument
operation. It is keyed, by the numbers in the lower,
right-hand corners of the blocks on the diagram, to the
detailed block diagrams. They provide an assembly-by-
assembly description of instrument operation.
8-7. The detailed block diagrams, in turn, are keyed
to the schematics on the Service Sheets that follow
them. These Service Sheets provide a stage-by-stage
description of the circuits on the schematics. The
stages are keyed to the descriptions by the stage names
that appear on the schematics.
NOTE
Table 8-3, Schematic Diagram Notes,
explains any unusual symbols that
appear on the schematics. The table
also explains the switch-wafer
numbering system.
8-8. TROUBLESHOOTING
8-9. This manual provides two methods to isolate a
problem to a particular assembly. The first method is to
use the results of the performance tests (given in
Section IV) and the table of Post-Repair Performance
Tests and Adjustments, found in Section V. More
information about this method is given in Section V.
8-10. Overall Troubleshooting. The second, and
primary, troubleshooting method is to use the overall
block diagram (found on Service Sheet 1) and the
troubleshooting block diagrams that follow it to isolate a
problem to a particular assembly or circuit. The
troubleshooting information on Service Sheet 1 explains
how to use the block diagrams.
8-11. Circuit-Level Troubleshooting. Once a
problem has been isolated to a particular assembly or
circuit, the text and a table on the service sheet that
documents that circuit give detailed troubleshooting
information for the circuit.
8-12. RECOMMENDED TEST EQUIPMENT
8-13. Test equipment and test equipment accessories
required to maintain the Signal Generator are listed in
Tables 1-2 and 1-3. Equipment other than that listed
may be used if it meets the listed critical specifications.
8-14. SERVICE AIDS
8-15. Posidriv Screwdrivers. Many screws in the
instrument appear to be Phillips, but are not. To avoid
damage to the screw slots, Posidriv screwdrivers should
be used.
8-16. Service Kit. The following parts can be ordered
for use in a service kit for the generator. (Before
ordering, check to ensure that they are not on hand;
most of them are common to service kits for other
Hewlett-Packard instruments.)
8-1
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