On 8/15/2016 7:54 PM, Jeff Findley wrote:
Percussive maintenance. Sometimes you really do want to hit it to fix
it.

Back in the tube days, it's amazing how often that worked.

One special case was old car radios. They had mechanical vibrators that
"chopped" the car's DC battery voltage so it could be transformed up to
the high voltage that the tubes needed. When those vibrators got old,
it took a good hard rap to the top of the dashboard to shock them into
operation.