Sunday, January 24, 2016

How to fix humming on the Polk PSW111

A few months ago I started noticing that even when I wasn't using my receiver my sub-woofer was making popping sounds at about 1 pop a second. Since I had purchased the sub-woofer about 3 years ago the warranty had expired so I was going to have to either fix it myself or get a new one.  Given a new one is ~$150 I decided to try fixing it.

Since the popping noise was periodic I figured it was probably a capacitor that had gone bad. These are the capacitors I replaced and what you'll need.  Note that I'm not sure which/what combination of these fixed the issue as I replaced them all at once.  I have a feeling you may only need to replace the 150uF power capacitor.

  • 1- 400v polarized 150uF capacitor (big one)
  • 2 - 63v polarized 47uF capacitors (the differently colored ones)
  • 1 - 35v polarized 100uF capacitor
  • 2 - 50v polarized 47uF capacitors
  • small amount of thermal paste
update: It seems like you may only need to replace the 47uF 63V capacitors, thanks to detailed investigation by Craig Brown (See comments below for details).  Thank you!

Here's how I replaced them:

  1. Disconnect the unit from power and your stereo system
  2. Open the back of the unit, there's like 20 screws (for good reason as the thing would shake itself apart otherwise)
  3. Disconnect the woofer from the circuit board (the pins are labeled so you don't need to worry about taking a picture yet).
  4. How comes the fun need to remove the screws holding in the large circuit board, however polk covered them in two types of glue.  I used a pair of pliers to kind of chop them off with a knife to remove the glue from inside the screw heads.
  5. Also remove the heat-sink supports (stuff will now get kind messy as there's thermal paste all over the place.
  6. You can now remove the board.  
  7. Now replace the capacitors.  Make sure to remember the polarization of the holes. If you forget I believe there's a crossed circle icon next to the negative leads. I used a desoldering gun to remove the capacitors, however many of the legs were still difficult to remove as the solder tended to stick to the legs.
  8. Put everything back together (may want to replace some of the thermal paste) and cross your fingers that it works! :)


  1. Wanna add to this post that replacing the Caps with new ones fixed my subwoofer that would work intermediate and would also generate ghost noise even with no input signal.

    I replaced
    2 - 47uF/63v polarized capacitors
    2 - 47uf/50v polarized capacitors (actually I used 47uf/63V. same as above)
    1 - 100uf/35v polarized capacitor
    1 - 100uf/20v bi-polar capacitor
    3 - 4.7uf/35V bi-polar capacitors

    I used an ESR and found that the two 47uf/63V were detective.
    I also found one transistor on the input/control board that was defect. Can't remember the Q-number, but part number is J105 (JFET N-Channel 25V, TO92 housing).

    Total cost less that $10.

  2. thanks Peter! Strange, I'm not sure what happened to Craig's post :(

    I had a periodic hum coming from the subwoofer. It didn't affect functionality, but it was quite annoying.... something unacceptable in my home theater setup. I replaced the two 47 µF 63V capacitors, and the hum is gone!
    Thank you so much for taking the time to research this and post the results! Absolutely Excellent!

    Thanks for taking time to research and post this solution. Replaced the 2 47µF 63V Capacitors ($0.82 ea.), a little thermal paste and everything is working perfectly.

  5. Does anyone have a link to these capacitors at an online store?

  6. Aluminum Electrolytic Capacitors - Radial Leaded 63volt 47uF 6X11.2mm LS:5mm Ammo Crimp


  8. Full details with links for parts here:

  9. Thanks for this post.

    I replaced the 2 - 47uF/63v polarized capacitors.

    The sub started working again. However, not very cleanly.

    I now have a very quick heartbeat as soon as power is applied. As well as a lot of low frequency crackling.

    I'm thinking I either have other caps that are bad or I did a crappy job at soldering these 2 caps.

    Any ideas?


  10. Hi,

    I recently repaired my friends PSW111 and found this post helpful. The FET Q340 on the pre-amp board was shorted, I used a NTE451 FET. Also, all but the large power supply capacitor (C24) were all out of tolerance. Especially the two 47uF/63V ones that measured 1 pF. The rest were 30 to 50% of their rated values.
    The Heartbeat was what my friend first complained about until it totally died so replacing all the electrolytic capacitors and FET fixed the problem.

  11. Glad to hear people are reviving these subs :)

  12. Great post! Can you tell me if the 2 - 63v polarized 47uF capacitors sit side by side, middle lower left side? Or can you circle them on your photo? Many thanks Alex!

  13. If you look at mrfxr link I think they're circled

  14. hey guys. does any one still have one of this PSW111 amps? i need to know the resistor on R57 and both on R56 on the amp board, mines are blown and cant read the writing on them.
    best regards

    1. Hey man I just stumbled upon this forum to replace my capacitors, but i do have a clean board none the less. I can't see the resistors because most of their numbers are underneath the actual resistor. But if you wanted I could take a pic of my board and somehow get it to you so you can read the resistors. That or you can send me a pic of your board with the resistors highlighted and ill tell you which ones they are. If you do end up seeing this maybe I can link up with you on reddit or something. I don't wanna give my email out on this random blog.

    2. Thanks for calling my blog random :) but seriously if you want me post an image here or something let me know

  15. Thanks for this, my psw111 was out of warranty, $2 of parts from my local store, and 30 mins later no more heart beat... My local store didn't have 47uF 63v so I used 100uF 63v instead. The biggest pain is getting off all the damm glue.

  16. I am having the same problem as everyone else.I've never changed a capacitor...I have no problem getting in but is it easy to solder? Going to order capacitors.

  17. I was recently given a 505 that does not work. The driver itself seems to work connected to another amp. I get a red LED when it’s turned on but no other response. Does anyone know where I can get a schematic or even better, what might be causing the problem? I’ve just started hobbying with electronics after 25 years away so I’m really just polking around at the circuits. :)

  18. How about if it does not have power?

  19. ordered my caps yesterday, hopefully it works out :D

  20. I'm about to do the repairs, and to replace all of the caps. Is the list provided by Peter on April 22, 2019, the definitive list? In the photo, where is the FET?

  21. The FET is on the input and control circuit board. It is not on the power supply/amplifier board.

  22. Hello and thank you,

    I finally repair my Polk PSW111 with the change of the two capacitor 63V 47uf.

    All for $ 2.18.

    The purchase of the Bose 700 Subwoofer will wait a few more months.

    Thank You.

    1. Eeeek! Don't waste your money on BOSE, get a quality sub from say svs!

  23. hello all. i just ordered the caps for this amp, and thank you for this fix. i have one question. my board seems to have a strange, but disconnected jumper wire topside, connecting an area marked for a C40 cap between the left 47uF 63V cap and the 50V 47uf one. does anyone else have this?

  24. How do you know the JFET is defective?
    I tested it with multimeter, it showed low 5 ohmh between source and drain at all times. I ordered the replacement (two items), and they all measure similarly low resistance. Which makes me wondering is JFET is the failing part...
    I started looking at the JFET since the capacitors measure within 20% below the nominal. Should I still be replacing the capacitors?
    My problem is with the noise all the time when the subwoofer if powered.

  25. I recently bought this guy: as a general purpose tester, I think it can test JFETs. Can see my latest post where I used it. Nice tool to have around.

  26. Going to be diagnosing my red led on at all times, psw-505. I ripped her open and no bulges on any of the caps from what I can see at the moment. Great to find this blog!!

  27. My Polk PSW110 also stopped working - no sound. Seems like I heard small noises coming from it one day when it wasn't even on. I normally connect it using the LFE input, but I tried connecting using the the speaker terminals and it seems to be working this way. Did anyone experience or try this out? Also would this help to identify which component has gone bad? Could it be the 47uF caps everyone is talking about or the FET? It does seem like there are a lot more than 6 caps on the board in the picture above. Does anyone have any help on how to identify which ones are the bad ones based on what I am experiencing?

  28. per my recent blog post I bought one of these: for testing out caps and it works well, and pretty neat at that :)

  29. Really solved. I changed only the first two 47uf / 63v and it is already working perfectly

  30. Had the same classic symptoms as others and decided to replace all caps while at it. Measured each of the 12 OEM electrolytic caps using my Fluke 289 with the following results, seeing which path per the web site is the better approach.

    150 µF @ 400 v = 145 µF
    120 µF @ 63v = 115 µF
    100 µF @ 35 v = 100.2 µF
    100 µF @ 25 v = 108 µF
    47 µF @ 63 v = 30.5-33.3 µF (Ah Ha, value continually scrolling through this range during measurement)
    47 µF @ 63 v = 40.2 µF (not so good either, but at least measured value stable during measurement)
    47 µF @ 50 v = 46.6 µF
    47 µF @ 50 v = 45.7 µF
    10 µF @ 63 v = 9.6 µF
    4.7 µF @ 35 v = 5.36 µF
    4.7 µF @ 35 v = 5.35 µF
    4.7 µF @ 35 v = 5.45 µF

    Verdict is in. Wouldn’t have known for sure that only the two 47 µF @ 63 v electrolytic capacitors were defective until going through this process. Looks like only replacing the two 47 µF @ 63 v caps is the best approach.

  31. I also just replaced the two 47uF 63V caps and it solved the problem of the speaker not working using the LFE input.

  32. Want to say thanks to OP, same issue. Replaced the 2 caps more heartbeat! So far so good (ok it's only day 1) but glad I can still use it without the heartbeat.

  33. I have this subwoofer, and I had this same noise symptom!
    I just recapped all electrolytic capacitors for the same value from Nichicon, and ..... another problem arose when connecting the subwoofer.
    It emits a "pop ... pop .... pop", and the led flashes at each pop, regardless of the position of the "Standby, Auto or On" switch!
    Does anyone have any idea what else could be going on?



  34. Hi Alex,

    Thanks for taking time to create this blog.
    I have the PSW111 with the heartbeat problem.
    Any suggestions on how to remove the plate that is stuck in the subwoofer box?
    Those 16 screws really had that plate stuck in there. I wonder if there is some adhesive / rubber gasket that is holding it in place. I don't want to destroy the finish while getting to a relatively easy repair.


  35. hmm perhaps try for the other side by removing the speaker? or seeing if you can get a credit card between the gap. Mine wasn't very hard to remove, there's no glue, just compressed foam.

  36. i unscrewed the woofer, then leaning it over toward the woofer, the woofer popped out. then i pushed on the plate from the inside. its not glued, just has a gasket and was a tight fit.

  37. Thank you very much. Changed the 2 capacitors of 47uF and 50V and that fixed the heartbeat I was hearing even when I had the subwoofer disconnected .

  38. I'm having the same problem on my PSW110. Could someone please indicate an acceptable thermal paste to purchase?

  39. Great insights about the capacitors and resolving the heartbeat issue. I have a PSW111 with that heartbeat, however, in addition, I get quite a bit of static crackling sound from the membrane when the sub is turned on, connected to an amp/receiver, and firing. Does anyone know if that is the capacitor issue? Or, is there an additional issue? Thx

  40. may be related, I'd start with the caps and see where you land after its done

  41. I have the same problem as Rdorigo (see November 5, 2020 at 10:44 AM)
    "It emits a "pop ... pop .... pop", and the led flashes at each pop, regardless of the position of the "Standby, Auto or On" switch"
    Any ideas as to what this problem is?


    1. Experiencing the exact same issue. Did you figure out what was wrong?

  42. To remove the back just use a larger sheet metal screw #10 0r 12 and just screw it into the metal plate so a holds and you can pull the plate up . I used a claw hammer.

  43. FYI a few years later and the 120uF 63v cap died, however also now I have no sound so something else must have broken

  44. Peter: if you're still subscribed to this blog, I replaced the 120uF cap however I'm having the symptom where the volume is very very low, I have a feeling it's due to the transistor you talked about on the input board. Did you replace that for a similar symptom? I hope this weekend to desolder it to test it out to see if mine is bad as well. I really need to buy an oscilloscope to better be able to diagnose these issues.

  45. Fwiw, I replaced most of the caps on this board and still had the same issue, but had found a potential issue on the circuit board in the process. A fried trace between a cap and transistor; I posted about it at the polkaudio forum about this issue:

  46. Hi, replaced the two 47uf caps with 100uf (what I had on hand) and that solved the "heartbeat" issue. Thanks for posting this!