SOLUTION HERE
I hate when threads end with no resolution, poor saps who come in later that have no idea what they're doing, have this same issue, only to turn up empty. I've fixed the Wii, it was an issue that seems far from common, and I hope nobody else ever has it.
If your sound isn't working, several things you can try before doing this are:
- Changing sound settings between mono, stereo and surround
- Testing the Wii on different TVs and through different AV cables
- Testing continuity for the LR pads on the AV out port (there are Wii pinouts online that show you which ones are for audio)
If those fall short, you likely have my issue, an issue that nobody else seems to have had or documented yet. Anyways, you're going to want to test the audio preamp chip on the motherboard. It's a small 8-pin chip on the bottom side of the board. It's close to the IC audio-video chip and sits right next to the AV port. It has a unique manufacturing symbol that looks like an A or an M, and should say AMPAM on it. This image I snatched from bitbuilt shows it off better.
You're going to want to test the two pins of the chip above indicated in red, then the two indicated in white. If your chip is bad, you won't get any continuity or read of any kind between the pins. I found a good chip gives me ~770 on my multimeter in just plain old continuity mode. If it's bad, here's the kicker - you gotta salvage one from a donor board. I've looked extensively for replacements, I have no idea where to find any. The company, the markings, they don't lead anywhere. Ampam didn't give me any lead as to who the manufacturer is, or any similar replacement components. You're likely better off just paying the 10 bucks for a donor board, sadly. Though, if anyone finds a replacement chip, do let me know.