In my experience, the most helpful approach to performing RCA on complicated systems involves several hours, if not days, of hypothesizing and modeling prior to test(s). The hypothesis guides the tests, and without a fully formed conjecture you’re practically guaranteed to fit your hypothesis to the data ex post facto. Not to mention that in complex systems there is usually 10 benign things wrong for every 1 real issue you might find - without a clear hypothesis, its easy to go chasing down rabbit holes with your testing.
That's a valid point. What I originally meant to convey is that when issues arise, people often assign blame and point fingers without any evidence, just based on their own feelings. It is important to gather objective evidence to support any claims. Sounds somewhat obvious but in my career I have found that people are very quick to blame issues on others when 15 minutes of testing would have gotten to the truth.
I agree with both of you. I think it’s sort of a hybrid and a spectrum of how much you do of each first.
When you test part of the circuit with the scope, you are using prior knowledge to determine which tool to use and where to test. You don’t just take measurements blindly. You could test a totally different part of the system because there might be some crazy coupling but you don’t. In this system it seems like taking the measurement is really cheap and a quick analysis about what to measure is likely to give relevant results.
In a different system it could be that measurements are expensive and it’s easy to measure something irrelevant. So there it’s worth doing more analysis before measurements.
I think both cases fight what I’ve heard called intellectual laziness. It’s sometimes hard to make yourself be intellectually honest and do the proper unbiased analysis and measuring for RCA. It’s also really easy to sit around and conjecture compared to taking the time to measure. It’s really easy for your brain to say “oh it’s always caused by this thing cuz it’s junk” and move on because you want to be done with it. Is this really the cause? Could there be nothing else causing it? Would you investigate this more if other people’s lives depended on this?
I learned about this model of viewing RCA from people who work on safety critical systems. It takes a lot of energy and time to be thorough and your brain will use shortcuts and confirmation bias. I ask myself if I’m being lazy because I want a certain answer. Can I be more thorough? Is there a measurement I know will be annoying so I’m avoiding it?
In my experience, the most helpful approach to performing RCA on complicated systems involves several hours, if not days, of hypothesizing and modeling prior to test(s). The hypothesis guides the tests, and without a fully formed conjecture you’re practically guaranteed to fit your hypothesis to the data ex post facto. Not to mention that in complex systems there is usually 10 benign things wrong for every 1 real issue you might find - without a clear hypothesis, its easy to go chasing down rabbit holes with your testing.