How to use a O'Scope: The proper techniques for using an oscilloscope are presented. From basic measurements to more advanced techniques.
Oscilloscope: Oscilloscope block diagram and schematics.
Principles of Testing Electronic Systems: Online lecture notes and book chapters about digital testing.
Testing: How to test those pesky transistors with a DMM or VOM.
The Oscilloscope: What is an oscilloscope, what can you do with it, and how does it work? This section answers these fundamental questions.
XYZ's of Analog and Digital Oscilloscopes: A very nice article on the actual use of O'Scopes.