Kenwood Powered Subwoofer SW-38HT

[mactypetim79]

Hello everyone!

One of my pending projects is a SW-38HT Kenwood powered subwoofer. Unfortunately, during my pre-sound check, I noticed that a capacitor was blown. Not just busted or bulged but burned to a crisp, making identification impossible. Anyone have access to a schematic, or perhaps can figure what the value of this cap would have been?

http://www.flickr.com/photos/107059463@N02/10565017734/

http://www.flickr.com/photos/107059463@N02/10565023874/

[kaboom]

Re: Kenwood Powered Subwoofer SW-38HT

Does this unit work fine otherwise?


That cap, being near the wires from the transformer, suggested to me that it was for noise suppression of the bridge rectifier.

The schematic confirms this. Both C31 and C32 are connected as such. You can use it without those caps; there may be slightly more noise on a nearby AM radio as a consequence.

Those ceramics are underrated for such use. There should really be two polyester or (larger) polypropylene caps for such duty.

Remove C32, on the other AC leg from the transformer and the other side of that connector, and try it.

[mactypetim79]

Re: Kenwood Powered Subwoofer SW-38HT

No, haven't turned it on yet - never got to that point. For audio equipment I do a visual check first and blow it out with an air compressor. Thank you for getting back so quickly. Did not expect that. I'll try your suggestions at work this Thursday.

-Tim

[kaboom]

Re: Kenwood Powered Subwoofer SW-38HT

No, haven't turned it on yet - never got to that point. For audio equipment I do a visual check first and blow it out with an air compressor. Thank you for getting back so quickly. Did not expect that. I'll try your suggestions at work this Thursday.

-Tim

You're welcome.

I got sort of lucky and found that service manual rather easily. More so than some others, which after a "google oogle," can be rather frustrating...

[mactypetim79]

Re: Kenwood Powered Subwoofer SW-38HT

Just tried the subwoofer and it thumps fine, though I couldn't isolate the sub enough to really tell if there was more noise, etc. I miss the older Kenwood receiver I used to use for testing! Sound seemed fine however with no distortion that I could hear.

I did remove that 2nd cap (C32), and there seemed to be no extra distortion on my AM shop radio. Now, I have to make a judgement call - is it ok to resell the unit now without those caps or should I replace and upgrade them?

[kaboom]

Re: Kenwood Powered Subwoofer SW-38HT

Just tried the subwoofer and it thumps fine, though I couldn't isolate the sub enough to really tell if there was more noise, etc. I miss the older Kenwood receiver I used to use for testing! Sound seemed fine however with no distortion that I could hear.

I did remove that 2nd cap (C32), and there seemed to be no extra distortion on my AM shop radio. Now, I have to make a judgement call - is it ok to resell the unit now without those caps or should I replace and upgrade them?

Aha- didn't know that you were planning to sell it.

Those caps are/were there for possible noise issues with weak signal reception. Which may be why you didn't notice increased interference.

I'd be tempted to replace them. I'll have to look, I may have some .047 100V MLCCs to give you. I've used these as SMPS snubbers and audio amplifier Zobels w/o issues. They're more than adequate for your application.

Edit:

I just checked the caps I have. I no longer have any .047 100V. I do have .047 50V.

As the two large electros are also 50V, it follows that each leg from the transformer does not exceed 35V AC. So C31 and C32 can be replaced with good 50V caps.

If you're still interested, let me know...

[mactypetim79]

Re: Kenwood Powered Subwoofer SW-38HT

Its been a busy month... finally got back to these projects after I got another receiver in with blown caps, and I just went to digikey and ordered for both units before I remembered your post.

Hold on to those caps. If you end up not using them, I may ask if something REALLY nice comes in