Background: Retired. Fixed income - not wealthy! 1.42gHz eMac Sept. 2005 Purchased base model and immediately modified with Plextor D/L optical, 250gb Maxtor drive, 1 gb RAM and Acer 17" LCD dual monitor- all third party because cheaper than from Apple. Therefore - invalid warranty. No problem. Never had a failure with Apple products.
Problem: The "jet engine" fan drives me crazy with noise! I modified the outlet to the fan [larger] and removed the transparent computer back to reduce turbulence noise. Added a speed controller to slow the fan. Works like a charm. Minimal noise. But. Twice now the room has been a little warm and while listening to iTunes through USB to iMic and to my hifi system I have overheated a chip[?] inside that has caused an 'alarming' loud buzzy noise to appear at all of the sound ports. Internal speakers, headphone out, USB - everywhere. Both times I have shutdown, let it cool off overnight, and all is fine in the morning. I know that whatever component inside that I am overheating will eventually fail with this treatment.
Question: Can any tech point me to the correct area inside to add extra small cooling fan? I am competent with electronics and high voltages [I build tube amplifiers] so I am not afraid to poke around and modify. I just don't know where to look.

Woah, hold on here! You are running sound through your iMic and you can hear a high static sound through your built-in speakers at the same time it happens? Wow...

The issue may not necessarily be a chip, heat, or anything that is easily fixable. The sound, when going through USB, is on a separate channel on the boards bus. Simply put you've got two completely separate systems with the same symptoms. To top it off, it's doesn't happen often enough to truly diagnose it properly. I dare say let it get hot again and find out if it has the sound issue again. The other two times could have been coincidences.

If you want to go poking in the machine and you believe it's heat related, replace the fan with something that has a bit more juice. It will be louder, but you can pick up a variable speed fan with a switch. Just turn the fan up when it's a little hotter

I would be supprised if it's a heat issue though. Then again nothing supprised me when Macs go bad. Tell us how it goes!

[QUOTE="whitlock"]Woah, hold on here! You are running sound through your iMic and you can hear a high static sound through your built-in speakers at the same time it happens? Wow...

:messenger3: No. Not at the same time! But I hear the same loud buzzy sound no matter if I pick the USB output, OR the headphone output OR the internal speakers. Get it now?

And it IS heat. It happens when I get really pissed with the fan sound and turn it down too low and the room is a little hot. It's very repeatable - although I'm not about to experiment because I don't want to cause a failure.

If you read my post you'd see I already have a speed controller.

I just want to know "where" the audio circuitry is inside an eMac.

Can you handle that one?

Looking at the service manual its hard to tell, but an educated guess would be that it isn't too far from the audio ports.
As has been postulated already, it may not be the audio circuitry which is causing the buzz. If you're getting it via iMic and via headphone jack, its quite likely that the buzz is originating earlier in the system, so to speak. Power Supply would be my first guess, after that its something in the system bus. eMacs have a rep for being quite overclockable, thats why the PSU is my first guess.
Whichever part is overheating, it proably runs hotter than anything else even when its running OK. Warm it up and feel for the most heat (hold your hand over it obviously). Thats where you need to point your fan.

Thank you. The warmest part IS on the right side where the power supply resides, and it DOES get progressively more warm than any other part as I turn down the fan speed. I'll investigate further cooling in that area.

Most typically issues in AIO (All In One) machines generate from an analog board (power), so I'd take waragainstsleeps advice on leaning towards the power supply on your culprit. Work from that angle, though like I said earlier and you kow, troubleshooting these issues can be a pain. Hopefully this is all that is wrong.