al446, of course one has to be extremely serious for in order for the Voodoo Repair procedure to work. It also involves painstaking preparation, such as listening to a Dr. John album while smoking datura stramonium.
Then we have "Percussive Diagnosis", a very useful technique for confirming the presence of loose contacts and bad solder joints. I often use it on musical instrument amps and amplified speaker cabs as these are particularly prone to this type of problems.
Applications range from macroscopic - a kick against the side of the cabinet, when followed by a loud cracking noise from the speaker confirms the existence of the problem - to microscopic where gentle tapping of the circuit board with a screwdriver handle will point out the exact location of said problem.