My JBL subwoofer just buzzes when I turn it on. It doesnt seem to change anything if I plug it into a powerstrip or the wall. It also doesnt seem to matter what setting it is on, all that changes is the sound of the buzzing. This sub has had very little use over the years and has been stored in an air conditioned space until now. What should I do? This thing cost me about $500.

The hum might be caused by the main semi-conductor device that produces the sound. Of course a capacitor might look normal and still cause the problem. The only way is to replace the big ones in the unit.

Seems the battery has gone bad prematurely. Charging circuits have to be good since the unit works fine off the adapter plugged into the mains.

hell no thats a fire hazard.. I am thinking that the surge is more that that unit can handle..surge is the extra power needed to start up an electrical piece of equipment..surge can easily double the amount of power required for startup..may need a new powerstrip with a much heavier rating..

I have the same problem. But after a short time it stops even in battery mode (i.e. unplugged). Did you find a solution in the meantime?

this doesnt help. how can i get back on?

If you turn the unit on with no input and get a loud buzz, and when you put signal to it and you cannot hear the music but the buzz (Probably more like a hum). Then most likely the amp is blown.

It can be bad filter caps, read the service manuals here: http://manuals.harman.com/JBL/HOM/Service%20Manual/PB10%20sm.pdf
http://manuals.harman.com/JBL/HOM/Service%20Manual/PB12%20sm.pdf

Or bad power amp module, take the voltage reading per SM, I mod my, http://s807.photobucket.com/albums/yy352/budm/JBL%20PB-12%20mod/

Yes it's probably just an Electrolytic capacitor.
If your any good with a soldering iron you could even do it yourself.
If you do have a go replace the big ones first.

Hello there..Thats normal only if your sub volume and the pre amp is turned up..Your amp is the cause of the speaker jump..Turn amp volume sub level down a few and check your wire from sub to amp..If all of that is good is a normal operation for pre amp warm up in sub if level is turn to max..Try unplugging amp freom sub then turn sub on stand alone(just sub outlet plugged in and no wires from base amp plugged in..If sub stops the its the amp making the problem..If it still is there then the pre amp is either dusty on inside or the outlet plug that it is plugged in doesnt have a good ground..Hope these help to solve your problem..Have a great day...

I’m happy to assist further over the phone at https://www.6ya.com/expert/joe_a3369546f8067589

The amplifier in the sub as with any other amplifier has a capacitor in it. Essentially a battery that holds a charge. When you trun things off such as subs or amps with a powerstrip instead of the intended on off button, the power supply has been cut, but the capacitor is still energizing the unit. So it catches the noise in the line.