Any audio/speaker techs here? Issue with Active Subwoofer

hikky_b

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Hi all, not sure if there's any A/V techs here?

I've inherited what looks to be a Hill Audio 15" Active Subwoofer (circa 1990's I believe) and having an issue with it.

The sub will power up and work for a short period of time but then start "buzzing" loudly. The cone looks like it get's pulled back and vibrates in that position.

I've checked all connections, different cables etc so I can rule those out.

I've attached a video below showing it working and then going to the 'broken' state.

Any ideas would be much appreciated. I will probably have to send it off but curious if it's something I could DIY.

Thanks!


View attachment powercubesub15.mov
 

garycrist

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Pull it apart and inspect/replace the electrolytic capacitors. They will be bulged or otherwise puffed out.
The 90's had a bad batch of caps back then and they do wear out too.
 

pete_c

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I agree with @garycrist. Capacitors going bad will be bulging or leaking. Have a look on the BadCaps forum for methodologies of repair.
 

hikky_b

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Thank you both! I was reading that the caps would generally be the first thing to check for.

Looks like it's got four 6800uf 100VDC. There are also 3 smaller ones on the main board.

To my eyes they don't appear to be leaking or bulging however?

Here's some shots:

subcaps.jpg subcaps2.jpg subcaps3.jpg
 

wittaj

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Did you change a light fixture recently or a on/off switch or change out light bulbs with LED?

I had an issue recently where my sub developed a buzz/hum when I replaced a light buib with an LED light bulb.

Come to find out there was a timer wall switch without a ground and one too many LED bulbs was causing pulsing down the line and would cause a buzzing sound. Go back to incandescent bulb and all was well. I had like 14 LED bulbs on that breaker and apparently the 15th was what compounded the problem.

As soon as I changed out that timer toggle switch to one with a ground wire, all was well.
 

hikky_b

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Did you change a light fixture recently or a on/off switch or change out light bulbs with LED?

I had an issue recently where my sub developed a buzz/hum when I replaced a light buib with an LED light bulb.

Come to find out there was a timer wall switch without a ground and one too many LED bulbs was causing pulsing down the line and would cause a buzzing sound. Go back to incandescent bulb and all was well. I had like 14 LED bulbs on that breaker and apparently the 15th was what compounded the problem.

As soon as I changed out that timer toggle switch to one with a ground wire, all was well.
I wish it was that simple! Unfortunately I get the same from my workshop which is on a different board to the house.

I've contacted a local AV guy who said he will take a look. I'll post back after he's seen the unit.
 

pete_c

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In the picture with the three caps the middle one (may be the angle of the photo) appears to bulge a bit.

Another thing you can try is while keeping the subwoofer open.

Turn it on and wait for the buzz then spray the power transistors / IC Amplifier with air to cool it off and see if the noise goes away.
 
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