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Tired sub amp

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Zurar

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I have an old pair of computer speakers that (when they work fully) still sound like the day I bought them. The problem I'm having is, the sub for the set will sometimes not come on while the satellites still sound flawless, so obviously the issue is only with the sub amp. Some strange things I've noticed about the issue is, if I put the sub output above 0 or 5 (-9 to +15 scale on the control dock) when I either turn the speakers on or start playing sound through them, the sub usually won't come on. Once the sub IS on though, I can crank it up +5 at a time and let it go for a little while before increasing it more until it's at max and it will work fine. I can't see any physical damage such as charring/burning on the board or bulging caps, etc.

Beyond capacitors, my circuit board knowledge is pretty limited. Anyone have any ideas what might be causing this issue? Thanks in advance for any help!
 
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Sounds like bad solder joint to me, good luck finding them, you could try oven baking the whole board to reflow the solder joints, but you can't see them visually often, even under 10X magnification as the solder bubble can leave a good skin but the core joint could be fractured.
 
Hmm, never thought of that. It does get rather warm inside. Wouldn't be surprised if it overheated a joint at some point. Worth a try I guess. Thanks for the suggestion.
 
There is always freeze spray. It can be used in two ways;
1. Cool the component
2. Cool the PCB while looking for discontinuities.

Manufaturer's shave cost by using 1-10 uF electrolytic caps as coupling caps because they are less expensive than metalized polyester. You should look there too. Sometimes an ohmmeter will find them, but an ESR meter is the meter of choice.
 
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