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Old 03-06-2012, 11:06 AM   #1
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Default Fixed (I think) my Klipsch Promedia 2.1 Subwoofer.

My subwoofer was cutting out and finally went off. I took off the panel which housed the amplifier circuit boards. As I was doing this, music was playing, and the subwoofer would play then not, and so on. I saw no damage. However, I took something nonconductive (used a pen) and tapped down on a relay. Now the subwoofer has been working for about 30 minutes.

Here was my logical conclusion for why it was the relay. The amplifier circuit worked sometimes, and sometimes it did not. That led me to conclude that it was either a loose connection or a relay (basically, anything mechanical, resistors/capacitors shouldn't sometimes work and sometimes not, they die). But my question is, why did tapping on a relay fix it for good?
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Old 03-06-2012, 11:11 AM   #2
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are you sure it was a relay? tapping may unstick a stuck relay contact temporarily. maybe it's got a cold solder joint on a terminal and tapping completed the connection. maybe the cold joint is elsewhere and tapping flexed the board and completed a broken connection.
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Old 03-06-2012, 11:22 AM   #3
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The cold solder joint is a possibility. The tapping resulted in inconsistent crackling from the speaker, not clean cutoffs which I was expecting.

The more I think about it, it must be a bad solder joint somewhere on the board. The satellites always work so it's not their 2 respective daughterboards. And when I'd have the panel tilted slightly one way or the other, I could get the subwoofer to play. So I will expect this subwoofer to quit playing sometime in the future. But it's still working, so I will not touch it :beer;

Last edited by us3rnotfound; 03-06-2012 at 11:24 AM.
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Old 03-06-2012, 11:51 AM   #4
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Is this the old or new Promedia 2.1 sub design? The old one had a huge a*s transformer and (IMHO) sounds better, but runs hot.
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Old 03-06-2012, 11:56 AM   #5
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This is the new one. I do agree, I had an older one that seemed to run pretty toastily. This one has the right-angle DIN plug as a plus though.

Actually let me add that I have owned about 3 Klipsch computer speaker sets - the 4.1, 5.1, and this 2.1. They're all great but they seem to fail after a few years. I think they are well-built and sound great, and the circuit designs seem to be really good in that they do not cut corners with cheap overproduced crap. They just carry some quality production problems that today's society doesn't have time for, which is kinda sad in that they truly are unique items.

Last edited by us3rnotfound; 03-06-2012 at 12:00 PM.
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Old 03-06-2012, 04:00 PM   #6
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Relay is easy to troubleshoot. Tack-solder a wire between the contacts it is closing. If that fixes it, it signals intermittent relay contacts. First measure the signal output resistance to be sure you aren't circumventing something working as it was intended to - a relay disconnecting output because there is a short in wiring or speaker. In this case it seems unlikely but taking something apart can move wires around and ... it's still possible in theory.

Relay contacts can foul a bit causing poor contact even if the relay mechanism itself isn't stuck. Cold solder joints can usually be found visually, and/or reflow any that are questionable.

The other option is you try to recreate the fault and you probe the board with a multimeter to see whether it's power or signal getting interrupted and where. Be careful when dealing with high voltages.
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Old 03-06-2012, 04:05 PM   #7
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Capacitors can sometimes work and sometimes not. Once I began to open a PC to see if it needed dust cleaned out. I was lazy and didn't power it off first. The slight movement of pulling the side panel off the case, jarred a capacitor just enough that it shorted the windings and the PSU protection circuit shut the system off.

I had no reason to believe bad caps until I had isolated the PSU as the problem, opened it and found a vented capacitor. However on a PSU circuit without monitoring and shutdown, a shorted cap would vent or explode before long.
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