that was semi-official repair policy for apple II computers in the
minnesota education system... turn it off, lift it up a foot or two, and
flat-foot slam it back on the table.

Actually, there's a number of old repair techniques like this that don't look
very professional, (Especially if the customer sees you do it.) but work very
well. For example:

A buzzing transformer lamination can often be cured by whacking the corner of
the laminations with a hammer.

On old Hammond organs, noise in the vibrato can be cured by pulling the
rectifier tube, connecting a clip lead to pin 8, reinserting the tube, turning
the organ back on, then touching the other end of the lead to the center pin on
the vibrato scanner for a few seconds. "Whiskers" in the scanner will be blown
to smithereens and cause no problems for years.