Sometimes, by hitting a certain spot on a piece of gear, you can cause an issue to occur or to go away.  You might think, "This repair should be simple since I know the problem's location."

Unfortunately, the cause of a simple problem isn't always so easy to find.

Newton's Cradle

Hitting gear is a legitimate technique for hunting down intermittent problems.  You might start by striking the unit at various places on the outside to help narrow down your search.

Then, when you're inside, you might tap more and more lightly, trying to find the location of a intermittent part, circuit board, or connection.  "Orange Sticks", a soldering aid, are often used for such tapping but any wooden or plastic stick can help.

The process can be tedious—consider the executive desk toy named Newton's Cradle:

A steel ball swings down and hits a row of other balls.  Only the farthest away ball pops up, all the others stay put.

When you tap on a circuit board, chassis, or wire harness, every distant part, wire, and solder connection gets the message.

Intermittencies can be microscopic, even quantum mechanical in semiconductors, and can be the most difficult of problems to track down.

If tapping lightly at a certain point effects the problem, the next step is to tap even more lightly around that point, trying to find a new, more sensitive point.  Hopefully, that new point will be closer to the problem's cause although, sometimes, one can be misled.

Other troubleshooting methods may help out, for example signal tracing, but they too are made more difficult by the intermittency.