Extremely Loud humming in Subwoofer - Promedia Ultra 5.1

[deb0]

Started happening two days ago:

When ever I turn on the speakers via the control pod, The subwoofer hums loudly. If I turn down the volume on the control pod, the humming increases. Man, I love these speakers and hope there is a way I can fix this.

thx,

[FireWave]

First Make sure all of the audio plugs are securely in. Then make sure the sub volume is at 0 or -2. If that sill doesn't help then unplug everything and then plug it back in.

[stpete cooling]

If the system does not hum when the input cables are removed from the back of the panel, it is likely that one of two 35v 100mFd capacitors on the main board have dried out. Whenever I repair these panels now, I always upgrade those two capacitors to 105 deg. Celsius rated versions (even on boards that are not yet humming). I believe one of two other places doing repairs is now doing the same. Much rarer is that one of the nearby 16v 100mFd capacitors has dried out. All four sit next to a heat sink that is always quite warm.

[Guest Anonymous]

Following this thread and http://forums.klipsch.com/forums/t/129378.aspx, my speakers started humming recently. First, a low hum that would go away if I turned the volume down, then a louder hum that wouldn't, and now it's loud enough that the speakers are unusable.

I'm not sure if it's the problem described here. The hum is (now, at least) completely unaffected by the volume knob. When I switch to headphones, it goes away and is heard in the headphones, also unaffected by the volume knob. The hum also continues for several seconds (more quietly) after powering down the speakers. The hum does *not* go away if I disconnect the inputs.

Any relation to those PCB caps? The above suggests it's a different problem, since the hum *doesn't* go away when the inputs are disconnected. (By the way, did you mean 100uF rather than 100mF?)

If it's those caps then it's probably moot to me anyway; I don't have the dexterity to solder in that space. I could remove the board that's in the way, but that's another disassembly job...

I may just wire the sub directly to one of the external speaker connectors and replace the whole amp with an external receiver. Except, since most cheaper (sub-$300) receivers apparently require a powered sub I'd have to buy a separate subwoofer amp, which brings the cost and hassle up significantly. Also, receivers designed for a PC environment, with a control unit like the Promedia and Logitech speakers rather than on-unit controls, are essentially nonexistant. Buying a whole new set of speakers is silly when the ones I have are perfectly functional and all I need is an amp, though (and upgrading to something with digital inputs would be a nice bonus).

[Guest Anonymous]

Oh well. Sort of regret buying these for the price, given how long they lasted (only a few years) and how unreliable the hardware apparently is for others as well...

[stpete cooling]

The fact that the hum does not go away when the cables are unplugged serves to verify that the problem is not in the signal source (e.g., sound card) nor input cables. The capacitors nearly always take care of the hum issue. Once I've installed 105 deg. Celsius rated capacitors, I have not had that hum return. It may help that my panels also have a fan moving air inside the sub enclosure, evening out the temperature and removing heat more quickly from the two heat sinks near those capacitors. 100 mFd refers to microFarads, same as uF, just as mmfd used to be micro-microfarads, and now is referred to as picofarads. (the F was sometimes capitalized in honor of Faraday, for whom the Farad unit was named).

Once the weak spots have been addressed, I've seen these systems perform well for years.

[CrimsonSky17]

Hi stpete,

I'd like to start off saying that I apreciate the input you've contributed towards this community. I too also have the problem of the amplifier hum and a steady hiss from my satalites. I replaced the two 35v 100mFd capacitors in between the two black heat sinks as you suggested. I turned the system back on without any input or speakers connected.

The low frequency hum was eliminated, however there is a slight hiss still coming from the subwoofer. Upon plugging the speakers in, the hiss is also still there, louder than the sub hiss, however it sounds like a cleaner hiss than before. Also, when I power down the system there is a brief squeek that comes from the amp.

You mentioned that there are 4 other possible capacitors that could have gone bad...Could you give a description of where I can find them on the board? Can the system still function if the first two capacitors have a bad connection?

Is there any other weak spots besides these 6 capacitors that can cause the type of problems I'm having?

Thanks!