Polk DSW1000 Amp - long time to power on

[rrands1]

realizing this may not be the right forum, but hoping an electronics whiz can help a brother out...

I have a Polk DSW1000 subwoofer w/ a built-in amp. The amp powers on OK, but will not start producing sound until after it has warmed up for anywhere between 10 and 30 minutes. After that time, it is not unusual for it to kick in for a second, then kick out, then kick in for 2 seconds, kick off, etc until it finally outputs sound continually, and then it will work OK until I power it off & let it cool down. Re-powering starts the process over again.

To my fairly novice mind, this seems like it might be a capacitor, so I pulled it apart today to look for any obviously bad (i.e. leaking) capacitors. I did not find any, but I did find two that have their tops swollen, and I wonder if they might be it..

Does anyone know the best way to troubleshoot those? I can de-solder them & put in new ones if I need to, but hoping there was maybe some way to test them while they are still in the unit?

Or, does it sound like I am off on my diagnosis, and maybe it's something else? Any suggestions on where to start looking? I can use a meter, but am not super versed on electronics. If I could find a shop to send it to, I would, but I can't find any shops that will work on it for some reason.

Thank you so much for any replies! I am attaching some pics of the two suspect caps...

[g1]

They're shot (the swollen ones). Replace them.

[The Dude]

Agree. Replace any bulged caps and see if that solves the problem.

[rrands1]

Thank you, gents! One follow up question - do bad caps exhibit the type of behavior I am seeing, in your opinion?

[The Dude]

Yes. Bad caps could certainly cause those symptoms. I like to think of it as a car battery that's going dead. When you put it on a charger or run the car for a while the battery may hold a charge for a bit. After the car sits a while, the battery is dead again.

[Enzo]

Caps CAN. But caps do a zillion things. Like wire. Imagine a piece of wire in your car. If it goes from the battery to the ignition, it affects the engine. But if it is just used to tie the trunk lid shut, not so much.

Amps have protection circuits, and power up delays to protect speakers from THUMP. A weak cap may not want to charge all the way up in such a circuit, and then the amp won't click on. But in another circuit, a weak cap might allow the amp to run but the sound would be hummy.

[rrands1]

Thanks, all - hoping those are it! There is so much glue on the circuit boards in this thing that it's hard to tell the difference between glue & cap puke - there are 3 larger caps (200vDC, 1000uf that are not bulgy on top, but the stuff at the base of them looks suspicious. I ordered an "in-line" cap tester & will check them out.

I appreciate the help!

[Leo_Gnardo]

About those "silent" periods, between the rare seconds that some audio does pass through your amp. It may very well be that the amp has a protection circuit which senses DC level on the speaker drive line, aka output, and handily disconnects your speaker if such DC is present. Because in so many amp failures, the amp emits a high level of DC voltage, with enough power to drive it, that it will destroy your speaker and maybe even cause it to catch fire. SO... if, after replacing some ragged looking capacitors, your subwoofer amp starts to straighten out and fly right, thank the designers of that amp for employing a protection circuit. Also understand that some amps have these so you might see it happen in other places from time to time and you'll know a little more about it than the average bear.

Good luck with the cap replacement and I hope your Polk starts acting right after you have done that.

[rrands1]

Thank you all *so much*! I replaced the two bulgy caps, and it now starts producing sound immediately! (YAY!!) But I have a new issue - now when I turn off the amp, it makes a "pop" like the woofer is getting a spike in sound. Any thoughts, suggestions, ideas on that? It was not doing that before, so not sure where to start!


Thank you - I appreciate any help!

[g1]

When you get your cap tester, test all the electrolytics. Some turn off thump is often normal, but if it did not do that when it was properly working, it may be another or several more bad caps.

[The Dude]

Agree. If dual rail power supplies don't turn on and off evenly (charge and decay), there is often momentary DC at the speaker. I suspect you replaced the caps that were obviously bad and bulged, but others are not up to snuff.