The questions we ask when we probe a circuit and observe the scope screen determine the information that will guide our troubleshooting. Here are some that can be helpful:
Is the signal there at all?
Is the scope setup correct? Is the front panel set-up proven?
Is the scope calibrated?
Is the amplitude expected?
Is the offset, if any, what is expected?
Is the frequency value measured expected?
Is the trigger stable? Is the scope set up correct?
Is the signal stable? If not, how much does it vary?
How do these measurements compare with previous measurements?
Additionally, we don't want to chase our tails. Measuring by objectives that are prioritized can
keep us on track with the mission at hand.
Some examples include:
(1) Signal Verification
Typical use here is to simply verify that the signal that you expect exists at the amplitudes and
frequency that you would expect. Don't forget to verify the trigger signal. Check cables/probes.
Comparing with a "golden waveform" can be helpful.
(2) Signal Integrity
Typical use here is to verify that your expected signal is pure and stable. Use of persistence,
jitter tracks, and histogramming critical parameters are common tests. FFTs can also be useful.
Remember to inspect your trigger signal too. Check cables/probes.
(3) Signal Timing
Typical use here is to verify that different aspects of the same waveform or different channels
waveforms are aligned in time as expected. Take as many measurements as time allows to measure
worst case jitter. Usually you need to measure ± 5 sigma (about 5 million) edges to see worst case
clock jitter.
(4) Signal Comparisons
After verification and integrity measurements, how does signal "A" compare with signal "B"? Ratio
or subtraction math can be helpful as can overlaying the traces. Are there trends of change in the
difference? Make certain critical measurements fall within needed specifications.