Self Test Overview - Keysight N5171B EXG Service Manual

Troubleshooting

Self Test Overview

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 or reported as faulty,
and therefore 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
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
4. The A5 CPU compares the detected dc level to the test limit. If the
5. If one or more detected values fall outside the limits, the most
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.
Keysight X-Series Signal Generators Service Guide
loaded into the A5 CPU memory.
to the A5 CPU assembly.
detected value is within limits, the A5 CPU reports a pass.
independent failure is determined and reported.
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