With a 13 year old's dawning interest in electronics and to the horror of my father, I opened the case up to see how it worked. Yes, I got in a lot of trouble for that vivisection of a very expensive piece of equipment. I didn't break it, I demonstrated that it was still in working order.
My subsequent experimentation with it went underground - I kept my exploration a secret - never working on it when my parents were home and always ensuring that it was reassembled and working by the time they returned.
It became my first hardware hack. I wanted it to have sound, a little plunk noise when the "ball" hit a paddle. I knew how to make a sound generator with a speaker and an oscillator from my Radio Shack 150 in 1 Electronic Experiment Kit.
The Odyssey was all hand soldered discrete parts with no ICs: lots of transistors and capacitors standing up above Bakelite circuit boards at wonky angles. None of the leads on the backs of the boards were trimmed. It looked really messy.
I started by probing the legs of transistors with a tiny Radio Shack analog volt meter. I'd get friends to play the game, so I could concentrate on the voltage levels. I found two places that alternately had higher voltage depending on the direction of the ball.
Thinking ahead, I realized that I could use that voltage to charge a capacitor. I don't recall the entire schematic, but I figured out how to charge the capacitor and then when the voltage dropped, dump the stored charge in the capacitor out to power an oscillator. If I used an electrolytic capacitor of about 10µF, I could get the oscillator to just chirp once before the power died. I placed one of these little circuits on each of the two places that I previously located.
The result was a satisfying plunk noise each time the ball hit a paddle.
I didn't keep the circuits, I had to restore the game back to appear to be unmolested after each experiment. Plus the oscillators were implemented in the Radio Shack 150 in 1 box and I wanted it available for other fun projects.
Forty plus years later, I still have a memento of the Magnavox Odyssey, one of the momentary push buttons from the top of one of the hand controllers: