Let's consider all the ways that technology is unreliable in the narrative and how it affects its users.
Amplification
The opening scene is instructive, setting the pace for the entire movie. Marty cranks up an amplifier for his electric guitar to eleven, pushing it beyond its capacity. He pulls out a pick and strums. The amplifier blows apart. The tech works too well. So much sound comes through that the amplifier is ruined, and Marty is thrown across the room into a far wall where shelves collapse, dropping a heap of Doc Brown's stuff onto him.So, there we have it. The theme for Back to the Future is that technology is awesome--we're literally awestruck by it--but it also has a tendency to fail. And the more awesome technology is, like speakers and amplifiers that take up the entire space of a wall, the more likely it is that tech will fail. It's also worth mentioning that this scene sets up the idea that the destructiveness of technology has the ability to physically move its users. The destruction of the amp shoots Marty across the room like the destructive capacity of the time travel machine will shoot him across time later. But rather than breaking shelves, the time travel machine will expose Marty's entire family to existential danger.
Car Engines
The DeLorean as a car and as a time machine is also unreliable. The engine won't start at critical times, meaning that the time traveling console doesn't always come up. Marty McFly has to crank the engine, pump the gas, and knock his head against the steering wheel before the engine roars back to life to channel the energy from the lightning strike to provide enough power to initiate the time travel sequence. And, of course, the lightning strike is needed because the time traveling machine is powered by a fuel source that is hard to procure in the '80s and essentially impossible to procure in the '50s.The unreliable time traveling DeLorean also thrusts Marty into a longstanding family conflict with Biff Tannen, a bully that tries to come between Marty's mom and dad. But Marty's greatest threat is actually himself. He has a natural confidence that his father doesn't have and more easily wins the affections of his mother. So, again, we have unreliable technology putting people in danger.
Photographs
Another instance of unreliable technology in the movie is the photograph. Marty keeps looking at a photograph of his family to see the effects of his presence in the '50s. His siblings fade away as the likelihood of his father and mother falling in love decreases. But, the theme of unreliable technology is at play alongside the narrative use of the photograph. The photograph loses its reliability. It doesn't record the image properly, erasing the past that it is supposed to store. It is another amp blowing apart or a vehicle refusing to start.Save the Clock Tower!
The clock tower is yet another instance of unreliable technology. It doesn't work and hasn't worked for decades at the outset of the narrative. Of course, a broken clock in a time travel movie is just about the most perfect image you could wish for, especially since the DeLorean is later powered by the event that causes the clock to break. Yes, the clock is broken in a time travel movie, signifying that time doesn't operate like it normally does. Don't bother looking at a clock to know what time it is--with time traveling clocks cease to report reality. The counting of time stops as a result of time travel. The interventions of time travel on the space-time continuum have complicated time-counting. Now, time doesn't merely progress forward. It branches and folds in on itself.And the clock is also dangerous. Doc Brown dangles from the hands of the clock high above the ground and nearly falls to his death as he wrangles with the wires he's connected to channel the energy of the lightning strike. Again, this is a perfect image for a time travel movie. The clock, symbolizing time itself, serves as a threat and a simultaneous safety line--Doc Brown clings to the hands of the clock for dear life.
The Future?
You might think that by the end of the movie, that everything has been put to rights and perhaps that breaks my idea that technology is unreliable. But everything hasn't been put to rights. As a result of time traveling to alter the past, the future is now skewed. Now, Marty will have to journey to the future to try to fix new issues that have arisen as a result of his interventions in the past. Technology just keeps breaking things.
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