volume is now poor

I really hate to say this but it sounds like you'll need to take it back to the store and get a new one. There are probably ways to fix it, but probably cheaper and quicker to get a new one. If you didn't buy insurance on it, I'd suggest doing so on the next one.

However, if you do want to fix it, I'd suggest putting the model number of the unit here or google searching for a "disassemble" guide once you have the model #. Maybe you might get lucky.