Well, I just sort of figured this out before the post, but I thought I'd post anyway because in searching online I found 2 or 3 posts elsewhere with a similar sounding problem, but no solution.
I've been experiencing, intermittantly, a problem with the Internal Speakers on my PowerBook. Sometimes... they just wouldn't work, and I would notice that in the Sound Control Panel, under Output, Internal Speakers weren't listed... just Headphones... but no headphones were plugged in... Weird... I thought maybe a driver went corrupt and wasn't listed anymore.
So I realized... I've been using the PowerBook as a DVD Player ever since I got the DVI-->s-video/composite dongle thingy (its awesome... I've discovered that when using it, it won't matter if the movie is in PAL if you have a NTSC TV... PAL will work, but I still haven't figured out if its actually doing on the fly hardware conversion, or just what is going on there), anyway, I realized I've been putting a lot of miles on the audio jack, so to speak. So I pluged in a cable to the headphone jack, unpluged it, did this a few times... and while watching the Sound Control Panel Output tab, the "Headphones" magically switched to "Internal Speakers" and back again as I was plugging and unpluging.
Aha!
Grabbed the ol' Can o' Compressed Air and blew out the jack for good measure...
Some sort of automatic hardware detection going on there? A light sensor? magnetic sensor? switch? really tiny sound engineer? dunno... but that did the trick... so, like I always say, when there is a problem, the first thing to do is jiggle the cable, the next thing to do is to hit or knock on it solidly (just to make sure it isn't stiction), and if that doesn't work... jiggle the cable again.
1. The PowerBook isn't really doing any direct PAL -> NTSC conversion. It decodes the video so it can be displayed on screen (using the VGA standard, which is neither PAL nor NTSC), and the video dongle simply takes whatever's on screen and outputs it as NTSC.
2. There are headphone jacks designed to disconnect a second source if a plug is instered, such as what happens when you plug headphones into a boombox. This is generally a mechanical function on part of the jack.
I thought about posting new topic about this, but since someone has the same problem, I thought I might as well post here.Anyways, what happens in my iBook is that when I plug in heaphones it doesn't recognize them (it says internal speakers on the sound CP), and when they do work, I get output through one side only (right side). I thought this might be b/c I just replaced lower case, and with the old case, you could jiggle the plug and get sound from both sides. The fit is slightly tight on the new case, and I can't jiggle the plug anymore. Any help?