Agilent N5161A/62A/81A/82A/83A MXG Signal Generators Service Guide
Troubleshooting
Self Test Overview
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Self Test Overview
The philosophy behind the self test is, “
It is better to pass a defective signal generator than to fail a good signal generator.”
The self test is
designed as a diagnostic tool used to check instrument hardware. The self test does not require the signal generator to be adjusted before
self-tests will pass. This philosophy implies that some failures will not be detected and reported as faulty, but will pass. If the signal
generator powers up, troubleshooting should always start with running the self test and resolving reported problems.
Embedded in the signal generator’s firmware is a group of self tests that should be used to evaluate the condition of the circuitry on the
assemblies. Self tests check hardware performance under controlled conditions and compare test results to predetermined limits. If the
results fall within the limits, the signal generator passes. If one or more test results fall outside the limits, the self test routine evaluates the
failure(s) and reports the most independent failure.
1.
When the signal generator is tested at the factory, the self test limits are loaded into the A5 CPU memory.
2.
When the self test runs, latches and DACs are set to known states.
3.
Multiplexers and ADCs route the dc signals from the selected test nodes to the A5 CPU assembly.
4.
The A5 CPU compares the detected dc level to the test limit. If the detected value is within limits, the A5 CPU reports a pass.
5.
If one or more detected values fall outside the limits, the most independent failure is determined and reported.
Independent failures can best be understood by using an example where there are three assemblies in a series: A1 is the first assembly, A2 the
second assembly, and A3 the third assembly. A1 output is the input for A2, and A2 output is the input for A3. If A1 output is defective, A2
and A3 outputs are also defective. If A2 output is defective, A3 output is defective.
A file in the instrument contains this dependency knowledge for the signal generator to use when identifying the most independent failure.
Therefore, if A1, A2, and A3 self tests all fail, the signal generator reports A1 as the most independent failure. If A1 passes, but A2 and A3
fail, self-test reports A2 as the most independent failure. If A2 passes and A3 fails, self-test reports A3 as the most independent failure. If
two independent failures occur, self-test reports only one failure at a time and reports the second failure after the first reported failure is
repaired. The troubleshooting procedure is based on the most independent failure and no lower level information is needed. Although not
needed for troubleshooting the signal generator, the self-test overhead provides features that enable you to view lower level detailed
information about the subroutines and to select specific routines to run.
These features include:
•
Select/Deselect Test
•
Select/Deselect All
•
Run Highlighted Tests
•
Run Selected Tests
•
Loop Selected
•
View Details - When View Details is selected, the measured value, lower, and upper limits are displayed for the highlighted test.
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