Wind wooshing noise in Presonus Eris Sub 8 sub speaker

[SFB]

While trying to fix a family members dead sub my Presonus Eris Sub 8 has decided to mimic gale force winds for some reason. I checked everything from trying a different wall socket, removed inputs and outputs, and checked to see if the volume has any effect (it doesn't)

I have read that the cause is likely a leaky DC filter capacitor which would make sense, but I don't have a schematic for this power supply and don't know my way around them well enough yet to know which might be the likely culprit.

I did also notice a few dry solder joints but would they cause the issue?

[SFB]

Re: Wind wooshing noise in Presonus Eris Sub 8 sub speaker

It seems a lot more of the signal is getting to the speaker than is supposed to - it isn't just the frequencies selected (ie under 80hz) It is making me wonder if the issue is actually on the other board and is not the power supply at all.

[CapLeaker]

Re: Wind wooshing noise in Presonus Eris Sub 8 sub speaker

Actually the bridge rectifier can make this noise too if only one of the diodes is shorted. And it sound like that too, with a hiss and a distorted sound. Mandatory I’d replace all the caps close to the heat sink first and check all the diodes in the bridge rectifier.

[SFB]

Re: Wind wooshing noise in Presonus Eris Sub 8 sub speaker

Ah, I did not know that. What is the long component with 8-pins that is attached to the heatsink (U9)?
If all caps checked okay with an ESR would that be sufficient? They are all glued to the board, I assume they don't want people repairing these.
Thank you again, it seems I am not having much luck with subwoofers at present lol

[petehall347]

Re: Wind wooshing noise in Presonus Eris Sub 8 sub speaker

that's the audio ic

[SFB]

Re: Wind wooshing noise in Presonus Eris Sub 8 sub speaker

Thank you.
I'm finding it very interesting how wildly different the same type of circuit can be constructed and how some of essentially the same components can look totally different. The other subwoofer has nothing that resembles that, just your typical chip type ic's.

Might have to look in my other subwoofer and another look in my 5.1 system again now I am starting to understand the general layouts and signal paths. Steep learning curve from just changing bad caps, resistors and diodes.

[Jay Ray Tay]

Good evening, I have had the same problem with mine. I tested the inputs as I suspected a sort at the input stage, but similar to here have arrived at the, power board, on mine one of the large surge resisters seem to be burnt out close to the heat sink, could this be the issue, or is it likely another symptom of the problem?

[прямо]

That looks like a 100 ohm 5% (brown black brown gold) resistor. What does your multimeter say when you measure its resistance?

It has no "burnt" appearance whatsoever though. Just a faded color code rings.

[Jay Ray Tay]

That looks like a 100 ohm 5% (brown black brown gold) resistor. What does your multimeter say when you measure its resistance?

It has no "burnt" appearance whatsoever though. Just a faded color code rings.

I thought the same, but it is physically twice the size of any other resister I've seen, so wasn't sure if the code was going to be standard or not. The colour has been distorted by the burn, but the one on the other side is definitely brown black brown gold... The burned one was touching the heat sink, and the capacitor right behind it, so I'll test that two to see if it's ok. I should be back in the workshop tomorrow afternoon so I'll test it then.

The other side of the resistor is black, and clearly burned, I was just trying to get the best shot of the Stripes to check the code, as the stripes are not visible at all on the other side.

[прямо]

They are not surge resistors, btw. Just a quick and dirty way to drop voltage by converting it to heat, hence the big physical size (probably around 2W-3W) What are the 3 legged ICs next to them? Linear voltage regulators LM78XX/LM79XX?

[Jay Ray Tay]

L7915CV, and the other side L7815CV.

[прямо]

Have you made any progress? This board is very easy to find faults (if any) because there aren't that many components to check.

[Jay Ray Tay]

Have you made any progress? This board is very easy to find faults (if any) because there aren't that many components to check.

Yeah the resistor I mentioned before is way out of tolerance, Reading above 130 ohm, the one on the other side is 99 ohm. And about 4 of the smaller caps close to the heat sink are not charging. I won't get chance to do the work, for a couple of weeks due to work commitments, but I'm going to try and get the parts ordered this week.

Thanks for the advice and support

[прямо]

130 ohm means the resistor is not blown, otherwise it would read open circuit or a much higher resistance. But it is indeed out of tolerance.

Before you order any replacement parts, I suggest you to check whether you are getting the correct voltages on those regulators.

7815 puts out +15V and 7915 puts out -15V.
Their input voltages should be at least 3V higher than the output.

[SFB]

Been a long time but finally getting back to this - it seemed to have mostly resolve itself but is consistently back now. I have upgraded my tools in the meantime so better equipped.

It seems like there is some form of noisegate that is flickering on and off, and measurements on the speaker cable seem to fluctuate as the sound surges as expected. There is no noise at all when the second board isn't connected and a static input on the speaker, which leads me to believe that's where the issue is. I did test the bridge diode and that is fine and did swap out a cap on power supply as was reading a high ESR just to be on the safe side. A few of the 50v 10uf caps on the second board are reading around 4ohm but are apparently within limits though tempted to switch them out anyway, and a few are around 3.5 whereas a new one tests around 1.4. It appears half on that board are NP. It sould be noted that adjustment of settings doesn't change the noise behaviour at all.

One thing I found curious was that on thermals the chip (MC4558G) directly below the PreSonus name didn't heat up at all whereas all of the others did though it seems to be part of the polarity circuit. The only other heat on that board were 2x 202 resistors (pictured).

Any ideas would be appreciated.