Diagnose/repair buzz/hum from Logitech Z2300 subwoofer - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 8 Old 09-02-2019, 07:56 PM - Thread Starter
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Diagnose/repair buzz/hum from Logitech Z2300 subwoofer

My Z2300 works fine but has developed an annoying buzz/hum coming from the subwoofer which can be heard when it is on in a quiet room but not playing anything. The hum has been gradually increasing over the past several years.

Some posts on the internet suggested removing a couple of wire crimp connectors and soldering them instead. I did this but it did not change anything.

There's the typical suggestion of checking for bulging capacitors, but nothing sticks out to my eyes. I've taken some photos to show as much of the board as possible. Pardon the image quality, as I have not freed the board from the wires keeping it captive to the cabinet. For reference here is another post of someone else's Z2300 with clearer photos of the whole board.

The tops of the capacitors look flat to my eyes. The two large Sanxon capacitors have a black "cardboard" on top which is slightly loose, but it's hard to tell if the surface below them is anything but flat.

Any tips on how to eliminate the hum? Does anything stand out in the photos?
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post #2 of 8 Old 09-03-2019, 07:42 AM
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I'll be interested in this thread. My subwoofer in the living room developed a hum too, but it isn't the subwoofer itself as I've tried another subwoofer there that I know doesn't hum in the basement theater and it hums also. And it just started one day out of the blue. I put in a ground loop thingy and it seemed to take it away for a bit but it gradually started humming again. And like yours, it's only when nothing is playing. I've never tried a different receiver though.
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post #3 of 8 Old 09-04-2019, 01:06 PM
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I had a similar buzz coming from both the sub as well as the satellite speakers on my Z-2300 system. Removing the crimp and soldering the connectors did not address my issue either.

What did work was replacing those two large Sanxon capacitors. They did not appear to be deformed, but I guess they started malfunctioning after 10 years.

It's a bit of effort to remove the board from the back panel (you have to unscrew the heat sink as well) but I replaced those capacitors with some that I found on Amazon (search 2pcs Nover LA 35V 10000uF 30x36mm LA Audio Grade Power Capacitor-5665), soldered them in, put it back together, and now the system is working again with no buzz on any components.
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post #4 of 8 Old 09-04-2019, 05:12 PM - Thread Starter
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Quote:
Originally Posted by amn2110 View Post
I had a similar buzz coming from both the sub as well as the satellite speakers on my Z-2300 system. Removing the crimp and soldering the connectors did not address my issue either.

What did work was replacing those two large Sanxon capacitors. They did not appear to be deformed, but I guess they started malfunctioning after 10 years.

It's a bit of effort to remove the board from the back panel (you have to unscrew the heat sink as well) but I replaced those capacitors with some that I found on Amazon (search 2pcs Nover LA 35V 10000uF 30x36mm LA Audio Grade Power Capacitor-5665), soldered them in, put it back together, and now the system is working again with no buzz on any components.
Thanks so much for joining to reply, @amn2110 ! Your comment gives me confidence to try replacing those two large 10000 uF capacitors.

Did you manage to remove the board without cutting wires? If I am forced to cut wires, I hope using connectors is ok in case I need to disassemble things again. Suggestions?

As you described, I can also hear the hum from the satellite speakers, but it goes away if I switch off the sub, which is why I suspect the sub (or its circuitry) as the source.

The noise has been bugging me for a long time, especially as it's in the bedroom. I've noticed a dramatic improvement in sleep quality in the couple of days since I unplugged it. I hope the fix can achieve silence, because otherwise I quite like these speakers.
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post #5 of 8 Old 09-06-2019, 08:26 PM - Thread Starter
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I changed the two large capacitors, but unfortunately the hum is still there. In case it makes a difference, the sound comes from, or is loudest at, the toroidal transformer. Any other suggestions to try?

Finding replacements locally was not easy, as most stores don't seem to stock 10000 uF units. Finally one store had some: Illinois Capacitor (IC) 10000 uF 50V 85C 35x35mm snap-in. They also had 35V-rated ones, but they were a fair bit smaller (maybe 30x30mm or less, I didn't measure) than the original's 35x30mm.

The Samxons both measured at ~12000 uF by my multimeter. At the store I also asked them to use an ESR meter and the resistance was very low, better than the replacements I bought. So it seems the Samxons are fine. The guy at the store was kind enough to suggest I could return the ones I bought if they didn't solve my problem.

For reference, I'll drop in this thread with lots of info and photos on the Z-2300 and its components: https://www.electro-tech-online.com/...former.114427/

As for the disassembly, I managed to remove the board by cutting only one wire--ironically the black wire on which I had previously removed a crimp and soldered together. It was quite a pain: dozens of screws, nuts, tons of glue all over securing many components, and even something like epoxy under the D-Sub connector. There is also what I assume is thermal paste applied with some strange plastic between each amp IC and the heatsink. That made a bit of a mess. I wonder if that needs to be reapplied after disassembly...

I also managed to remove the speaker wire without removing the speaker (getting the grill off is a pain since apparently it is glued). It required a lot of patience, contortions, and using a webcam for remote viewing. I've included a (blurry, not enough space to focus!) photo of the inside of the (upside down) sub, which at least shows the wire order: red then black, going clockwise from behind the speaker.

I'm really not looking forward to disassembling everything again to swap out the capacitors again... and mostly just disappointed the problem isn't solved.
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post #6 of 8 Old 09-10-2019, 04:39 PM
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I did not have to cut any wires but I did disconnect the the board from the power when accessing the board to solder in the new capacitors (the 4 pin connector near the top left with the red, yellow, orange, green wires coming out of it).

I saw the same weird plastic pieces near the heatsink and tried to put them back as best as possible (didn't add any additional thermal paste). Agree with you that it was quite a pain to disassemble with all the glue.

Not sure where else to go - maybe it is related to one of the smaller capacitors. This video on Youtube titled "The sound of bad filter caps - hum and ghost notes" had a similar sound to the buzz that I was hearing, which led me to replace the 10000 uF capacitors. Not sure if that is the same buzz you hear?
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post #7 of 8 Old 09-11-2019, 06:48 PM - Thread Starter
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Quote:
Originally Posted by amn2110 View Post
This video on Youtube titled "The sound of bad filter caps - hum and ghost notes" had a similar sound to the buzz that I was hearing
Thanks for the reference. That's a great video and perfectly describes the buzz:

I also compared to a 120 Hz test tone and it matches, as explained in the video.

Unfortunately, I made things a lot worse. I swapped back in the original Samxon 10000 uF capacitors. In addition to the usual hum from the transformer, I now hear the buzz loudly amplified through all speakers (satellites and sub) if I switch the power on at the control pod. Right now this makes the speakers totally unusable.

Maybe my soldering went badly or I kept the iron on the board too long. I think a couple of metal sleeves came out of the through-holes for one of the capacitors which was a bit difficult to remove. I tried resoldering to no avail.

The smaller capacitors look ok. I don't see loose wires or bad solder joints, which was an issue I previously fixed for the headphone jack on the control pod.

Perhaps it's time to take it to a repair shop, because I can't think of what else to try.
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post #8 of 8 Old 09-11-2019, 08:16 PM
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Darn sorry to hear that. Yeah, repair shop seems like the best bet.
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