Question Pioneer S-21W Home Theater Subwoofer suddenly stopped working

AlastairJake96

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Firstly just some details:

The Subwoofer as the title implies is a Pioneer S-21w (yeah, it's more of a stop gap atm but wasn't expecting it to pack up this quickly)
Connected to a Denon AVX-540BT Home Theater AV System.

The story, if you're sitting comfortably:
I've had it for a few months now, bought it second hand but worked perfectly when I got it home (yay). I found it a little underpowered (not unsurprisingly) but I was pleased with it for the most part. A month ago I turned it off for various reasons. Once I finished my set-up (for now anyway) I turned it back on and thought nothing more. The blue light indicating it's received a signal from my AV system would turn on once it detected low enough frequencies, what you'd expect.

It wasn't until I plugged my PC into my setup for some downstairs gaming a week ago that I began to suspect something wasn't working correcty - as I set-up the 5.1 surround sound - I noticed when the test tone was sent to the subwoofer the light would come on but... no sound. Weird, tried a few basic troubleshooting options but no change - no big loss I thought, but when I felt curious enough I decided to do a test tone through the Denon, no sound, oh no.

I've already gone through a few steps, the Denon has 2 sub pre-outs so tested both - as I said the light comes on to indicate that it's reached the lower frequency limit so, the Denon is definitely sending a signal, and the Sub knows it's getting a signal.

Next best guess, blown speaker? Well I got a multimeter specifically to test the speaker and low and behold, I get a reading around 3(ish)ohms (it's not infinity which is the main point).

So I'm at a bit of a loss, I've taken it apart and looked at the speaker, checked the cables for breaks using the multimeter, all checks out, the capacitors all look in good order according to my very ignorant eye.

If anyone can suggest anything I've missed please do, I'm happy to give you any info I've neglected to share and below is a link to some pictures you may or may not find helpful.

My Subwoofer in Pieces
 
You could put a voltmeter on the output of the amp....or the speaker terminals.....set it to AC volts....send a tone.....and you should see voltage especially if you turn it up....not in the neighborhood of millivolts though....you should see values above a volt if you turn it up. If you don't....the amp isn't outputting.
 

AlastairJake96

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You could put a voltmeter on the output of the amp....or the speaker terminals.....set it to AC volts....send a tone.....and you should see voltage especially if you turn it up....not in the neighborhood of millivolts though....you should see values above a volt if you turn it up. If you don't....the amp isn't outputting.
Well interesting. Had a play around with it and assumed it likely just be a static 0.00 but I kept occasionally seeing a voltage read on the multimeter. After a while, it seems that if I tap one of the rods (while the other is in constant contact with one of the output rungs) it will read a constant voltage around 0.5 to 1.1 but as soon as I hold the rods onto the output for longer than a second it goes to 0...?
 

AlastairJake96

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What rods are we talking about?

It sounds like maybe a bad connection.
Sorry, I'm not great at explaining myself. Ok so my testing setup is using the two metal rungs on the PCB that directly connect to the woofer itself. The rods I referred to are the two instruments(?) - one black. One red - connected to the multimeter.

What I was doing initially was sending a tone through the subwoofer from the Denon with the black measuring instrument (plugged into the multimeter) constantly in contact with one of the metal output rungs on the PCB, and the red measuring instrument (again from the multimeter) in constant contact with the other output rung on the PCB. This would give me a 0.00V on the readout of the multimeter.

I found out that if I was to tap either the black measuring instrument (please tell me what the official name is haha) or the red on its respective output rung it would give me a constant voltage on the readout.
 
It's sounds like the rods or whatever....are just the +and - speaker terminals (or connected to them).

If you tap on them and get a voltage....it sounds like maybe a bad connection.

You may be able to find it....although sometimes they are buried.

It may also be a bad component.

At least you know it's something IN the subwoofer.....and probably not the speaker.
 

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