How did smacking electron tube TVs help?
This practice is generally known as 'Percussive Maintenance'.

Any touching contacts, for instance in connectors, valves and their bases, and between the wiper of a potentiometer and the track, have a tendency to build an insulating film between the contacts. This happens most readily at higher temperatures, in high humidity, and when there is airborne contamination, especially sulphides. This can introduce higher resistance, non-linear behaviour, or break contact altogether. It can produce intermittent behaviour, changing with humidity, or voltage across the junction.

Sending a mechanical shock through the equipment can move the contacts with respect to each other, disrupting the film, and restoring contact.

In the case of a TV with a loudspeaker in it, sometimes the vibrations from the audio will change the contact state.

High contact pressures, and gold plating, improve the reliability of contacts against this sort of problem. TV valves, because they got hot, were especially vulnerable, and of course they aren't used these days.