Installation guide

Troubleshooting
Self-Test Failures and Related Troubleshooting
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Self-Test Failures and Related Troubleshooting
Overview
The philosophy behind self-test is, “It is better to pass a defective signal generator than to fail a good signal
generator.” Self- Test is designed as a diagnostic tool used to check signal generator hardware. Self-tests do
not require the signal generator to be calibrated before self-tests will pass. This philosophy implies that some
failures will not be detected and reported as bad, but will pass. If the signal generator powers on and
self-tests can be run, troubleshooting should always start by running self-tests and resolving reported
problems first.
Embedded in the signal generator’s firmware is a group of tests (self-tests) that can be used to evaluate the
condition of the circuitry on many of 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 failures
and reports the most independent failure.
1. When the signal generator is tested at the factory, self-test limits are loaded into the A12 CPU memory
from devices on each assembly or from fixed files. Most assemblies contain limit information while
microcircuit limits must be loaded.
2. When the program runs, latches and DACs are set to a known state.
3. An analog multiplexer routes the detected dc signals from the selected rest node to the A12 CPU.
4. The A12 CPU compares the detected dc level to the test limit. If the detected value is within the limits, the
A12 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 bad, A2 and A3 outputs are also bad. If A2 output is bad,
A3 output is bad.
A file in the signal generator contains this dependency knowledge for the signal generator to use when
identifying the most independent failure. 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 to view lower level detailed information about the subroutines and select specific routines to
run.
These features include:
• Select/Deselect Test
• Select/Deselect All
• Run Highlighted Tests
• Run Selected Tests
• View Details
When View Details is selected, the measured value, lower, and upper limits are displayed or the
highlighted test.