Bad driver or bad crossover?

[astrodog]

I recently purchased a set of used sierra-1s that are in excellent condition. Unfortunately, one of the speakers is playing sound only through the tweeter. The woofer has no sound coming out of it at all and even the tweeters sound a bit faint. My plans were to upgrade to nrt tweeters anyway, and since I know that the new tweeters come with new crossovers, i'm hoping this will fix this problem. Thing is, i'm not sure if it's the crossover causing this in the first place. Is there a way to find out which it is?