The best way to check the function of your subwoofer is to first turn it all the way down. Then remove any connections coming into the subwoofer from your receiver. Then bring any source component (such as a CD/DVD player, a VCR or even a cassette deck) close to where the subwoofer is. Run an RCA cable from the audio output of the source component to either the right or left line level input on the subwoofer. Then start playing a CD (or tape) and slowly turn up the volume on the subwoofer. You should be able to hear bass information coming from the subwoofer at a moderate volume setting.