My right phone on my headphone isn't producing sound

It's busted. You can try fixing it, but it's a pain in the ass to expose the wire and try to reconnect it using heat or something

You should buy a new one
 
buy new headphones or learn to enjoy only having sound out of one ear
 
Well when this occurs, some wiring inside is damaged due to too much strain on it. It can be caused by too much pulling on it or yanking on it. Of course, it's not necessarily on accident or purpose; this can be due to wear and tear.
 
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