PSW505 Popping sound changed to a heartbeat and static noise

I have two PSW505 Subwoofers. two weeks ago I noticed one of the subs making a popping noise which quickly changed to no sound except for static and a heart beat sound that doesn't stop even when the input is disconnected. Now the second sub is starting to make a similar popping noise but it's sporadic and the second sub is still working. Seems strange that both subs would start having issues within a few weeks. I haven't made any changes to the audio system other than adding an xbox to the receiver. Any ideas what has happened to these subs that are only two years old with moderate use?

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  • Thanks for the advice. yesterday the second sub stop working also. I will contact Polk CS during the week. I hope your right about the warranty. I have been very impressed with these subs until now.
  • GrahamWGrahamW Posts: 3
    Before I start scoping my PSW505 amp for the "heartbeat" problem (without the aid of a schematic) I'd love to hear from anyone who saw the previous post and has since "been there, done that" with a possible fix.
    Applying power triggers a regular heartbeat thump at about 2 beats a second. The beats gradually slow down until they are replaced by bursts of static. The static stops after a few seconds and then the unit works perfectly. Switch the main power off for a few minute and then back on and the amp behaves normally unless left off for some time.
    The problem does not happen after the unit wakes up from standby, but it's only going to get worse. The unit is out of warranty. Polk declined my request to release schematics. They would be happy to sell a replacement amp but I'm guessing the price would be about the same as the current closeout price for a brand new unit.
    These were not the answers I'd hoped for, but at least I was able to navigate Polk's relatively straightforward AVR and connect immediately with a polite human that I could understand!
    I did find a post suggesting the Klipsch RW-12 amp is a close relative and located that schematic. The designs appear conceptually similar but the Klipsch is too different to be of much use. Both the Klipsh and early PSW505's incorporate a Bash board, so it may be that earlier units are a closer match. Thanks for all help!
  • FestYboyFestYboy Posts: 3,583
    Start at the power supply, specifically the rectifier circuit and the caps associated with it
  • GrahamWGrahamW Posts: 3
    Thanks FestYboy, you make the logical suggestion but the power supply checks out perfectly. The problem turned out to be electrolytic capacitor C14 on the amp board (22uF, 50v, 105C). The capacitor had been mounted in physical contact with an adjacent 1W resistor that probably runs hot enough to dry the capacitor out prematurely.
  • FestYboyFestYboy Posts: 3,583
    Thanks for the tip, I currently have 4 and am waiting for one to give up on me... Was expecting something more dramatic, but it seams like it's just a matter of poor component placement that can easily be rectified.
  • GrahamWGrahamW Posts: 3
    Cough; the initial claim of victory proved premature (like - that's never happened to me before!) After leaving the unit without power overnight, a slightly different popping resurfaced, albeit for less time before the unit started working.
    So ... I removed the remaining seven small electrolytics from the amp board and checked them with a capacitance meter. All were low, only the 330uF and two of the remaining five original 22uF's were within the usual -20% low end spec. All others, including the 10uF 50v, were off by as much as -85%.
    Capacitors must be lifted to check them, so it takes no longer to simply replace old with new. That's what I did and would advise others to do. The 330uF 16v (adjacent the PCB mounting bracket) could probably be left alone, but I had one on hand and threw it in for good luck.
    The unit sat without power overnight and behaved normally when first powered up today. Fingers crossed!
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