I have a 5.1 Logitech Z-640 audio system that used to be hooked up to a Desktop we have that no one used and sat unplugged, and when I got my own desktop, I decided to claim it as mine since no one used it. All 5 speakers and sub still work, but there is an issue with audio that goes to the Center/Sub speakers. I know it is not the wire, but something on the center speak which has the audio controls. When trying to test my audio with the windows Speaker Setup, audio comes through the FrontLeft, FrontRight, RearLeft, and RearRight speakers, but nothing comes out of the Sub and Center. When listening to videos and games while the computer is in 5.1 or quadraphonic, the base still makes sound, so I'm going to assume it outputs the low sound signals that are for the 4 working speakers. While fiddling with the dials on the center speaker and testing to see if any of them are the problem, I found that the one labeled "center", which I'm assuming is for making the sound centered, more to the left, or right, appears to be the issue. I believe this because when using Speaker Setup and making it test Center and Sub while I move the dial, the speakers crackle a bit and you can hear the test sound, sometimes I am able to get a decently loud, but I'm sure not as loud as it should be, sound from them, but when watching videos or playing games, you can hear the audio cut in and out from the center speaker. Am I correct to assume that the dial is a variable resister that is going bad? Or would it be something else? If it is a bad VR, I can find a replacement one easily and swap it myself; the hard part will be opening the control panel on it, I think.