Subwoofer Power Supply Problem

[Bob in St. Louis]

Re: Subwoofer Power Supply Problem

By the way, any of you thinking the repair isn't worth it, should check >> THIS PAGE << for a review of the product, including it's original MSRP of $599.


Bob

[999999999]

Re: Subwoofer Power Supply Problem

I'm a little confused Bob in St Louis, your C78 and C66 don't look blown, did you pull them off and do an ESR test to find them faulty?

As for the large red wire, trace the circuit as it might just be an alternate location. I wonder if they moved it at some point because they found the adjacent capacitors were prone to fail so they didn't want the wire with its cement fortification impeding removal of a faulty capacitor.

The review you linked makes some very curious claims like Tracking Down Converter topology supposedly sensing input signal and lowering voltage, and yet I see no subcircuit on this PSU that would provide that functionality... and having read that it makes the review statement that an "Intelligent Parameter Control System... monitors woofer voice coil condition and sends data to the amp to correct and prevent..." seem all that much more dubious.

Don't get me wrong, it looks like a nice sub well worth repair and the hiss may be bad caps even though they don't look vented in the picture. I think I'd go ahead and replace C16, C17, C18, and C19 while the board and soldering iron were out... they're going to be inexpensive and possibly a bit degraded by the heat which was the likely cause of the C66 and C78 problem... ideally picking a 105C rated part.

[sfox]

Re: Subwoofer Power Supply Problem

I replaced the same two caps Bob mentioned, C78 & C66 , I used some Nichicon 1000uf 35 V radial caps I had on hand. The bad ones were Rec brand and one of them was swollen. I'll get the other values & complete the repair soon because I'm getting some odd pops at random times through the sub. I have a heatsink that I may mount to the plate, maybe that will help.

[999999999]

Re: Subwoofer Power Supply Problem

^ Pops seem more likely to be AC line spikes.

[ben7]

Re: Subwoofer Power Supply Problem

I replaced the same two caps Bob mentioned, C78 & C66 , I used some Nichicon 1000uf 35 V radial caps I had on hand. The bad ones were Rec brand and one of them was swollen. I'll get the other values & complete the repair soon because I'm getting some odd pops at random times through the sub. I have a heatsink that I may mount to the plate, maybe that will help.

It may be a bda connection that makes the pops, or like what 999999999 said,
it could be AC spikes. My computer subwoofer pops and crackles when you turn the fan on in the other room.

-Ben

[avanilla]

Re: Subwoofer Power Supply Problem

I replace all six of these for posterity (not including the two large ones). All is well and I am enjoying my "new" old sub.

[Bob in St. Louis]

Re: Subwoofer Power Supply Problem

999999999,
Thank you (and all) for the replies.
I did not check the caps. I blindly chose these two to purchase based soley on the information I found on the net (here included).
Granted, there's nothing better than a solid working knowledge about what your'e working on, but hey.... <insert nervous laugh here>

Now you have me worried I'm about to do all this for no reason.
I grabbed my Fluke83 and selected the 'cap' setting. With the leads on the caps terminals, the ohms went from near zero to into the Mega ohms.
Then I selected the DCV range and checked the cap and it reads about 0.3 volt DC.....steady and holding.

I did the same with the new cap, and the results were the same.
If what I did was a valid test, then you are indeed correct and these caps are good.

None of the caps have visual signs of defect, yet the symptom I have is the same all of these units exibit.

Thanks all! Happy Thanksgiving!
Bob

[999999999]

Re: Subwoofer Power Supply Problem

^ I'd go ahead and replace all those electrolytic caps (besides the largest higher voltage ones, for now), especially if your hum sounds like the typical 120Hz double line frequency type which does tend to indicate insufficient power supply smoothing... actually, knowing others have them failing and having the board out already I might replace them even if there wasn't any noise present yet.

lol, then again being a tweaker, I'd probably reverse engineer the PSU board subcircuit for that zener/transistor regulated portion and replace it with +/- linear regulator ICs... idealizing, not knowing if there'd be an audible difference which is hard to know unless someone has two units like you do so they can A/B test one after the other, with and without any modifications.

If you have a headphone you don't mind cannibalizing, you could take the drivers and wire them to probe-like tips and listen to the preamp stage output on the sub's amp board to determine if you hear this hum. If it's already present it is probably due to the caps we're discussing, but if there is no hum yet, not until after the power amp stage (through the sub speaker NOT the headphones since it's too high a level for headphones) then it would probably be the largest high voltage capacitors to blame.

Another option is setting multimeter to AC and measuring ripple on the rails of both the low and high voltage subcircuits but I don't know what threshold values would constitute pass or fail for this.

[Bob in St. Louis]

Re: Subwoofer Power Supply Problem

Thanks Nines!
So was my little DVOM test a valid one?

I've love to perform a A/B test of a mod such as the one you describe, but lack the finances. As it is, I'd just like to get these working so my son can rattle the house and I have an excuse to yell at him. haha

Bob

[999999999]

Re: Subwoofer Power Supply Problem

^ I was under the impression all that meter could test was small value uF capacitance, or charge time for an estimate of higher value capacitance. I'm otherwise unfamiliar with ESR testing on that meter. That it held the voltage tells you it isn't shorted or extremely leaky electrically, but I don't think the resistance test is valid (I could be wrong)... also, replacing with a high quality, low ESR 105C capacitor, the ESR should measure lower than the cheapy caps they used even if the originals were functionally within specs still. I wrote a bit more in my prior reply after your subsequent one, it seems my posts are never really final drafts...

[Bob in St. Louis]

Re: Subwoofer Power Supply Problem

I thin I see where you're going with the headphone test, however I don't have a pair I could use, much less cannibalize. neat sounding test though.

My thought mehind using the DVOM on the cap was this....On the face of the voltmeter, the cap test happens to be the same knob position as the Ohm check. knowing that, also tells me that as soon as I drop the leads across the cap, the 9volt battery inside the Fluke would be charging the cap. So the digital bard graph on the Fluke that races from near zero ohm into the Mega ohms would be the cap charging
-- am I wrong on that? --
So then, if I'm correct, the cap now hold a DC charge. That's when I could switch the meter to the DCV setting.....and that's when I'd get the .3volt reading.

Although, I could be damaging caps and my meter based on my cockeyed lack of real intellegence.

Since I bought the two caps, and have a long weekend ahead of me, I may install them, put it all back together and see what happens.
If I do, I'll let you know the result.

Bob

p.s. I feel this was a great thread until I came along and derailed it with my lack of basic eletrical knowledge.

p.s.s. By the way, I'm not hearing a 60Hz, or even a 120Hz noise. This is a harsh buzz, with intermittant severe movement of the driver involved. At times (on a bad day) the driver can move what loooks like nearly an inch.

[999999999]

Re: Subwoofer Power Supply Problem

Yes as the cap charges it should appear as a rising resistance until it reaches the peak voltage the meter uses, but even a defective cap that isn't shorted could reach a peak resistance value. Your meter's manual may describe a test involving the timing of charge to determine the capacitance for a large value cap (but I don't know if it includes one this large) but I would not be comfortable assuming anything about ESR without an ESR meter or test jig meant to measure that.

If the severe movement of the driver is while a signal is applied it could be some kind of interaction from unstable power. 60/120Hz hum isn't a steady signal, it does sound harsh but fairly repetitive.

I don't know what the rest of the sub looks like. Other things that can cause noise include a leaky transistor, it could be a mere TO92 sized, 6 cent part causing this. Without an amp schematic it may be beyond the scope of a forum post to try to guesstimate that, but briefly with no signal to the amp if a transistor isn't being biased much if any and the output is higher than it should be per the hFE spec on its datasheet, it is suspect.

Basically you just probe all around the amp looking for signal or power irregularities, if the power amp stage is a chipamp IC instead of discrete, or at least a transistor driver IC with transistor output pairs it becomes more easy to troubleshoot. The other option is to just start replacing anything inexpensive, since a lot of parts can be replaced for a few cents each. The adjustment dials (POTs) on the back complicate things a bit, I'd also turn all those back and forth several times to see if there is a POT wiper contact issue, after a while the springiness of the wiper may decrease and/or the grease can harden effecting the contact.

[Bob in St. Louis]

Re: Subwoofer Power Supply Problem

OK, gotcha.
Of what I understood of your post, I am incapable of performing.
What I didn't understand.....well......there we have it. haha

Thanks Mr. Nines.
I do believe I'll replace the caps this weekend and post the results.
Good point about the POTs. I've got some of this stuff to clean all of them.

Thanks!
Bob

[Bob in St. Louis]

Re: Subwoofer Power Supply Problem

SUCCESS!

I removed the old caps and found the bottom of one of them was a little discolored. Looks like some "juice" had leaked out and corroded the metal electrical lead.
In the picture, are four caps, it's the one on the far right.

I replaced them with the two on the left. Note the temp ratings.

The sub is dead quiet with no hum, no buzz. In fact, it's so quiet that I thought I left something disconnected, as it was almost "too" quiet.....

....until you feed it some music, then it ROCKS!

So there's one subwoofer fixed, I've got one more to go. Not bad for $5.76.

[Bob in St. Louis]

Re: Subwoofer Power Supply Problem

Done.

Number Two is finished, and works perfectly.
Looking at the time since my last post, that's how long it takes to fix one of these. Of course it's always faster the second time you do something, but in reality it's an easy repair.

$6 to fix two subs with an MSRP of $1200.

Rock on dudes.
Great thread. Thanks to ALL who have posted.

Bob

[pcrx]

Re: Subwoofer Power Supply Problem

Hey, New to the forum - an AVS regular though... I just ordered up a new Dayton amp for this same sub with the same problem... I am going to dig open my amp and see if I can replicate the successes others have had here before installing a new amp.

[nutty08]

Re: Subwoofer Power Supply Problem

This is an admittedly embarrassing question, but I just replaced all the caps on the PS as described here, but since I took it apart 3 weeks ago, I can't remember where the subwoofer posts go! Dumb mistake I know, but does anyone have a picture with the sub still wired in, or can described where they go. Thanks
-josh

[nutty08]

Re: Subwoofer Power Supply Problem

Nevermind, I figured it out from the pics above. I have a new problem after replacing the 6 caps mentioned above though. I started with the very loud hum problem that started suddenly in the middle of the night. Now, after replacing the caps, I just get a "popping" sound, maybe ~120hz or so, with mild in/out movement of the woofer. Putting signal on the inputs does not change this and I get no music/sound from the woofer. Any ideas?

[999999999]

Re: Subwoofer Power Supply Problem

^ Use a multimeter to probe the power supply board, checking that the voltages are doing what is expected/tolerable ranges. Also check that all your solder joints are good and no caps are in backwards. Do you feel this problem is one that is persisting, even if it were overshadowed by the prior problem, or is it an entirely "new" problem?

[999999999]

Re: Subwoofer Power Supply Problem

^^ Additionally, while I don't know if it is the problem, if your 2 large caps on that board were bad too it could cause this.