Will Bueché

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Computer repairs continued

Posted in Personal by Will on Friday, October 17th, 2008 ~ 12pm

Spent some time last night trying to figure out what is causing my computer to send noise to my stereo. It has gotten worse. Now if I touch the computer, particularly if I touch anywhere near the trackpad, there is noise. I believe the sound card lies directly underneath the trackpad, so my suspicion is that years of pressure has finally worn out something underneath.

Of course my initial suspicion was a grounding problem, but it expresses itself even when running on battery (which would eliminate any ground loops). No, there is something wrong with the sound card inside. Could be some wire has worn through its protective plastic sheath. Could be a loose wire. I tried half-heartedly to remove the case last night but did not. Cracked it open enough to blow air into it, but that did not help.

Tonight I will try something radical: “There was one hardware solution that one person said worked for him involving removing the palmrest and puting anti-static film between the bottom of the touch pad what ever is under it.” I am going to try that.

Further info: “This is not a typical ground loop problem in that it is not 60 Hz noise generated from external power line current induced in the ground side of the audio cable. The noise is digital hash generated inside the computer which appears at the ground side of the audio out jack (and perhaps on the ground of the PCI bus as well) as potential energy. When a cable is connected to the audio out, the resulting ground loop gives this potential energy (voltage) a path to flow as current through the audio cable. The cable acts as an antenna inducing the hash noise into the hot side of the audio cable and reflecting the noise back into the gain stages of the audio circuitry inside the computer. So the external ground loop is not the cause of the problem, but rather the path that gives the already existing internal noise voltage a place to flow. All electronic devices generate EM/RFI noise, especially digital circuits, fan motors, power supplys, etc. With proper internal shielding and grounding this noise should not appear anywhere in the audio path, and certainly not as induced current in the external cable grounds.”

Nonetheless I am going to stop at RadioShack and get a ground-loop breaker anyway. They’re only $17 and if it works, great. If not, at least I learned.

Update: The ground-loop breaker minimizes the noise when the noise occurs — i.e. it is no longer so loud as to trigger the stereo’s safety-off feature. But the noise still occurs. So although some of the noise must have been traveling through the ground part of the wire, the rest of it is present in the audio. So like the description above suggested, something is leaking electricity into parts that don’t expect it.

Update: I slid a piece of plastic between the trackpad and the stuff underneath it, but, there was already a layer of plastic there (installed by the manufacturer). No effect from adding more.

The replacement sound card should arrive soon, but I am worried that the laptop may not be powerful enough to run a second sound card without a serious impact on performance of my other applications. I typically run 3 key programs at the same time — Firefox, Photoshop, and iTunes. Adding a soundcard to it, which, because it is a plug-in, will use some more resources, may be too much for it.

So I am considering the possibility, if it comes to it, of a MacBook. I’ll continue that in another post.

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