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Model 11848 A
Service
Troubleshooting
General
Troubleshooting the HP 11848A Phase Noise Interface usually begins with troubleshooting a problem
in the HP 3048A Phase Noise Measurement System. Several programs in the System-supplied main
software can assist in isolating the fault to a System device. Details on these programs are found in the
HP 3048A Reference Manual for the System or in the main software under the Help function. Some
general guidelines are discussed below. It is usually more efficient to use these programs until they point
to the Interface as the faulty System device; the Diagnostic program is then loaded to troubleshoot the
Interface itself.
Troubleshooting Helps in the Main System Software
Some of the features in the main software which are useful in isolating the faulty System device are
found in the following list. To call these programs, go to the main menu and press the softkey labeled
Spcl. Funct'n. A menu of Advanced-User Rinctions will appear from which the programs can be
selected or other menus called.
Calibrate System. A series of transfer function measurements are made on various signal paths in
the Interface. The measurement data is stored as calibration factors which the controller uses (either
directly or in more involved calculations) to correct the measured phase noise data whenever that signal
path is used. Normally the Calibrate System program is invoked only for the annual System calibration
or when the Interface has been repaired. Any difficulties encountered when the calibration program is
being run may point to the Interface. For example, a catastrophic failure of a high-pass filter in the
Interface will generate data that is too far out of limits to be accepted as a legitimate transfer function;
the program will then abort the measurement.
Performance Tests. To verify that the system meets its published specifications, a series of
Performance Tests can be run. The failure of a test may contain enough clues to point to a failure
in the Interface.
Internal Adjustments. Often small out-of-specification results of the Performance Tests or Functional
Checks can be corrected by means of adjustments, particularly if the condition is due to a dc offset
voltage that is out of limits.
Functional Checks. These tests are an extension of the Performance Tests that test the general
operational integrity of the Interface itself. The test limits are generally loose. (The tests in the
Diagnostic program are similar to the Functional Checks, but they attempt to diagnose the failure
in addition to simply indicating out-of-limits data.)
HP 11848A Control. Arbitrary and complete control of the programmable functions of the Interface
from the controller keyboard is provided by the HP 11848A Control program. A single display contains
all the Interface state information. Because of the compactness of the state information, you should
consult the HP 3048A Reference Manual when running the program. (The keyboard control feature of
the Diagnostic program is similar to this program.)
Troubleshoot Mode. When the Troubleshoot Mode (a subset of Test Mode) is enabled, information
beyond simple error messages can be invoked. For example, tests can be aborted to the HP 11848A
Control mode which shows the Interface state when the abort occurred.
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