How do I debug with a scope?

[Skruffyhound]

Would anybody be kind enough to explain how to systematically debug using a scope please?
There are references all over as to how much a scope can help with debugging but not much about the steps one should take.
I understand the idea of using a function generator/scope for tuning/testing of circuits, but for debugging, what is it that makes a scope more powerful than a DMM?

Thanks

[anchovie]

You can view AC waveforms. It's like a silent audio probe! You can also check the output of a LFO.

[G. Hoffman]

To expand on that just a bit (I'm just starting to learn to use a scope, so I'm far from an expert), a DMM gives you a reading for a particular instant or the average over a period of time.  But it doesn't do a very good job of showing you how the signal changes over time.  An o'scope allows you to see how a signal is changing during a period of time.  As you follow your signal through the circuit, you keep track of what it is supposed to be doing, and when it starts doing something different you have localized your problem.  In addition, the nature of the distortions to the waveform should be visible, which may well help you figure out why you are having a problem. 


Gabriel

[Processaurus]

You can follow your audio every step of the way in your circuit and see where it's getting screwed up, and in what way.  You can view real time transformations to the wave (usually a function generator) as you turn knobs, or sweep the frequency or amplitude.  You can visually compare the input signal to any point in the circuit.  You can see if DC is really DC, or if not, what is happening to it.  You can trigger off the power line, and see if 60 cycle is the source of noise.  You can trigger off a transient, and view what happened in other parts of the circuit in that nanosecond.  You can scale the time resolution way out, and get a marching line of what has happened over the last few seconds.

Basically you can fix and design stuff knowing a lot less, by poking at things until the waves look how you want them to.

[Processaurus]

A construction tip is to wire resistors or a loop of wire as test points so you can easily hook up a scope probe to the outputs of the different stages of the circuit.  Also always handy is a loop of wire soldered to a ground bus that is big enough for the scope probes ground clips.

[Skruffyhound]

Thanks guys, between this thread, my own hands on research and the great Pdf Brian posted
here  http://www.diystompboxes.com/smfforum/index.php?topic=82173.0
the picture is becoming more clear.