The Logitech Z-2300 is a 200 watt THX®-certified 2.1 speaker system with a 8-inch long-throw subwoofer. I’m not going to tell you about how good or bad the system is because this is not a review, there are plenty of good reviews out there, just google for one. My Z-2300 worked perfectly for about 2 years but during the thirds year or so I started noticing a small hum coming out of the subwoofer no matter if it was a low or high volume, input connected or disconnected. It bothered me for quite some time but then I got used to it, until recently when I felt that the hum had increased its intensity and I couldn’t stand it anymore.
In the past few weeks I was constantly thinking that I need to fix it someday but I was thinking that I’m going to need to replace some capacitors that’s going to need some de-soldering, getting the right replacement soldering back together, this proved to be a wrong assumption as the fixing was much easier.
First of all you should start by removing the front grill. I used some small flat screwdrivers inserted between the grill and the plastic ring, first lfet-right, next top-bottom. I think the grill was glued a bit and took some force to get it to move. I managed to take mine out without any visible scratches or dents. There’s also a video on youtube, the guy recommends a hair drier: http://www.youtube.com/watch?v=cqbkMGPtZUU
Next you have to remove the 8 screws holding the woofer in place, after those are out slowly take out the woofer, hold it strongly cause the big magnet on the back might jump&stick to the toroidal transformers on the bottom of the subwoofer case. Remove the connectors and take the woofer out, this will allow us to pull the PCB on the back further out so we can work on it. If the zip ties holding the cable secured to the box are too tight you can cut them, but be careful not to cut any cable, and make sure you have replacements cause you don’t want the cable to be moving around synchronized with the bass 🙂
Next move on to the back of the subwoofer. Here you’ll have to take out all of the screws(22 of them) surrounding the metal plate. Now the backplate is kind off glued and stuck if you never opened it before so you’re gonna have to grab the heatsink firmly and give it a good twist as well as pulling on it, but be careful cause all the wires are attached to it and you can only pull it back about ~4 inches. After it pops out, look for the wires that are keeping you from pulling it further back. I had the woofer wires (black+red), I had to cut some more zip-ties to release them, and I could finally take a look at the board.
Although its hard to spot in the picture above, I spotted a potential problem. It’s circled in red in the photo. It should help you understand whether your problem is the same as what I have experienced, it’s one of those crimping connectors used to secure 2 cables together.The black cable (ground) originally comes from the toroidal transformer placed on the other side of the box. Then when it comes close to the PCB I don’t why the guys from Logitech decided to split it, and have another small piece of black wire going to the PCB. I really don’t understand, couldn’t they’ve just used a whole piece of cable? Anyway as I was talking to a friend of mine, this seems to be a very common cause for getting noises in amplifiers, broken ground circuit.In my case the crimping connector wasn’t holding the cables tight anymore so there was an imperfect ground connection from the transformer to the PCB.
In the above pictures you can see how I removed the crimping connector and I soldered the two ground wires together. Next some heat shrink tubing to protect the connection and the noise was gone. Put everything back together and now I can even pump up the volume to the max with the input disconnected and there is very little noise coming out of the speakers. No wonder the z-2300 has SNR >100 dB and they’re THX®-certified. I hope this helps you if you have the same problem.