Polk Audio PSW350 No Balls

[mmartell]

This thing has no guts and a really muddy sound. I took the backplate/amp off and have these measurements on the eight pin connector J6 which goes from the amp to the input board.

Pin1 0v
Pin2 -13.97v
Pin3 0v
Pin4 0v
Pin5 +51.7v
Pin6 -51.8v
Pin7 +14.54v
Pin8 -14.58v

Do these look good or... ?

[mmartell]

Re: Polk Audio PSW350 No Balls

Some pics...

[mmartell]

Re: Polk Audio PSW350 No Balls

Alrighty then...

From some of the other subwoofer threads I think I have all voltages present ?

Is it good practice to just replace the electrolytics on the board first ?

[momaka]

Re: Polk Audio PSW350 No Balls

Does this sub use a linear transformer? Looks like it to me with that bridge rectifier next to the two big caps.

Muddy audio could be from the small caps on the "amp" board. But it could also be if one of the main (big) caps is bad or starting to fail. Do you have an ESR meter? If yes, now would be a good time to pull some caps and measure them. That said, take precaution around the big caps - they could still be charged even long after you disconnected the amp. Moreover, even if they are not fully charged, more than 5V could still damage your ESR meter if it's one of those eBay/AliExpress kits. So beware of that.

[mmartell]

Re: Polk Audio PSW350 No Balls

I do have an esr meter and have tested the smaller caps in circuit with it and the readings lead me to take your advice and pull them for further testing.

Will report the readings back when done.

And yes it's a linear transformer.

[mmartell]

Re: Polk Audio PSW350 No Balls

I pulled C8 and C9 the two CapXon 22uf/50v caps between the large filter caps. One read 22uf 5.5ohm esr and the other read 18uf 7ohm esr.

Some esr tables indicate they should be about an ohm or less and others tables say these are fine. I suppose it depends some on the application so are these toast or still ok ?

[budm]

Re: Polk Audio PSW350 No Balls

This unit has linear power supply and linear amplifier.
What DC Voltage do you have on the speaker terminal?
Can I see good high res pix of the bottom side of the power supply/Power amp board?
What is the P/N of the IC U1 on the power supply/Amp board?
Can I see pictures of the Audio input board?
What is the history of the unit?
The speaker is good?

[mmartell]

Re: Polk Audio PSW350 No Balls

I had to put the caps back in. I read 0mv on the speaker terminals that doesn't seem right but then that was without input (it's still mostly apart)

I do not have a history on the unit it was given in trade for a few other things. It was supposed to be working and sat for some time before I tried it.

The speaker measures at 3.2ohms on my meter and was functioning previously just not with any power or thump. Much lower volume than I would expect even with the gain turned up.

Pics you requested in next post.

[mmartell]

Re: Polk Audio PSW350 No Balls

Amp board
Bottom of amp board
IC U1
Input board

[stj]

Re: Polk Audio PSW350 No Balls

what the hell is "muddy" ??
if you have no bass punch - but highs and mids are o.k. then it's a lack of instantanious current caused by weak bulk smoothing caps.

[mmartell]

Re: Polk Audio PSW350 No Balls

Hard to tell if the highs and mids are ok since by definition a subwoofer rolls them off rather quickly. But your point about instantaneous current may have merit. Are the bulk smoothing caps the large main filter caps ?

[momaka]

Re: Polk Audio PSW350 No Balls

Are the bulk smoothing caps the large main filter caps ?

Yes.
Did you check those too, by the way?
They rarely fail, but when they do, that's exactly what you get - "garbled" bass (similar effect to when you grossly clip an amplifier output.)

I pulled C8 and C9 the two CapXon 22uf/50v caps between the large filter caps. One read 22uf 5.5ohm esr and the other read 18uf 7ohm esr.

Some esr tables indicate they should be about an ohm or less and others tables say these are fine. I suppose it depends some on the application so are these toast or still ok ?

If they are 5 x 11 mm cans or smaller, they still might be "within tolerance". But at those measurements, I'd say they are getting closer to their EOL. It also depends on their series - i.e. if these caps are low ESR series, then 5 to 7 Ohms is more than likely too high / out of spec (check their datasheet to confirm, if it's a low ESR series.) If they are just general purpose series... eh, just change them anyways, if you have spare replacements. Above 5 Ohms is getting a bit lousy for a cap.

[mmartell]

Re: Polk Audio PSW350 No Balls

Ya I changed the smaller ones and same result. Maybe this sub is just for shit ?

Seems I can't trust the readings on my esr meter. At least not the capacitance readings, some read grossly under spec but read ok with my DMM. The main filter caps read about 1000uf low on my esr meter but they won't measure at all on my DMM so not sure about their health...

[mmartell]

Re: Polk Audio PSW350 No Balls

Where can I take some measurements to troubleshoot this ?

[mmartell]

Re: Polk Audio PSW350 No Balls

Anyone ? Could use some help with this one...

[momaka]

Re: Polk Audio PSW350 No Balls

Seems I can't trust the readings on my esr meter.

In that case grab some new and/or known good electrolytic caps and try measuring those. If you get iffy readings, then you know something isn't right.

At least not the capacitance readings, some read grossly under spec but read ok with my DMM.

Checking caps with a DMM is mostly pointless. I only do it occasionally to check for suspect electrolytic caps that may possibly be short-circuited... but that's very rare.

The main filter caps read about 1000uf low on my esr meter but they won't measure at all on my DMM so not sure about their health...

1000 uF low is just a hair below the 20% lower end of spec for those caps, so they definitely look suspect if the readings from your meter are to be trusted.

Also, what ESR did they show? This is far more important than the capacitance.
As for the DMM test... again, it's mostly pointless. But if you do want to do it "right", then you have to short the capacitor's (+) and (-) terminals every time before attempting to check them.

Where can I take some measurements to troubleshoot this ?

Report back what you find on the main caps above with some numbers (ESR and capacitance) - that is, after at least verifying your meter with some known good caps.

If the main filter caps seem alright, then I think the next thing to do is to isolate the audio between the output amp and pre-amp. That is, you'd be inserting an audio signal directly at the amp output IC / output stage to see if the distorted signal is there. If not, then the distorted audio is more likely originating from the pre-amp section. To verify that as well, you can insert an audio signal into the sub the regular way and see if the audio (or at least bass) comes out properly from the pre-amp section or if it's distorted.

[budm]

Re: Polk Audio PSW350 No Balls

Dual OP-AMP C358C on the power amp board, the signal from Preamp board is fed to R13 which goes to pin 6 of the C358C Dual-op amp. You can use audio probe (PC powered speaker with 1K resistor and DC blocking cap on the input to the to PC powered speaker) to check the signal on the leg of R13 to goes to the connector (cannot see the designator) of the power amp that goes to the preamp board.
Please see the spec of the IC:
C358C DUAL OP AMP, it is used for driving the output section of the amplifier.
HA17324 Quad op-amp
I would check Voltages of the IC power supply pins (V+/-).
You can use audio probe to trace the audio signal at output pin of the Op amp.

[mmartell]

Re: Polk Audio PSW350 No Balls

momaka,

My dmm has a capacitance setting and it works fine but can't charge up those large filter caps to get a reading. So I'm not just checking for shorts I'm getting actual readings, at least on the smaller caps...

Also the sub does not output a "distorted" sound - the problem is in the lack of volume and punch in the sound.

I too am curious if the problem is in the input stage...

[mmartell]

Re: Polk Audio PSW350 No Balls

bud,

As I would expect a lot of what you've said has gone over my head but I can certainly check the supply voltage of that ic.

Will look into using a diy audio probe as well.

[budm]

Re: Polk Audio PSW350 No Balls

OK, "Also the sub does not output a "distorted" sound - the problem is in the lack of volume and punch in the sound." Thanks for the clarification on that, just lack of punch.