If a subwoofer is not outputting any audio, no longer powering on, or is powering off within a few minutes, the first thing to check is the subwoofer's built-in amplifier.
Please Note: This is geared towards "home theater" subwoofers, not the subwoofers that come with our soundbars or computer speakers.
To do this, let's try something called a "buzz test":
- Make sure the sub is plugged in, powered on and has a sub cable plugged into the LFE port on the back of the subwoofer
- On the back of the sub, turn the gain knob up to at least 50-60% (about 12 or 1 o'clock on the dial)
- Do not plug the other end of that sub cable into your receiver or sub output
- Instead, grab the unplugged end of the cable and touch the male RCA post a few times to see if you can hear the sub give you a "buzz" sound each time you touch the post
HERE IS A PICTURED EXAMPLE OF A SUB CABLE WITH THE RCA POSTS HIGHLIGHTED
If you do not hear any buzz each time you touch the RCA post, then the built-in amplifier has likely gone out and will need replaced/repaired.
If you do hear a loud/pronounced buzz each time that you touch the RCA post, then the amp is likely still in working condition. In which case, if the sub passes the "buzz test", but is still not outputting any sound, you should then move on to checking the cone woofer. Please see the article - Troubleshooting the Cone Woofer of a Subwoofer