That’s where the phrase “out of whack” came from. You just needed to give it a whack.

I had a similar thing on an old crt monitor. The screen would start to flicker badly after a while, and 8 year old me found if you banged the side, just right, it would keep working for a couple of hours.

Turns out the circuit board had some dry solders on it and when I hit it on the side where the board was, it got the connection back for a while.