Ask Max: How can I get my iMac's headphone jack working again?
I bought an iMic because my iMac's headphone jack stopped working, and I learned that sound output from a CD was much better through an iMic. First problem: some sound came out of my external speakers; some came out of the internal speaker. Second problem: Switching back to Built-In Output in my System Preferences, Apple Mail stopped producing its New Mail and Message Sent sounds.
The headphone jack stopped working when the iMac was stolen and returned. Possibly the thief damaged the jack, or maybe the circuitry, trying to hook it up.
The iMic is a very decent solution to broken internal audio ports on your Mac computer. The only issue is that the internal headphone jack may have an intermittent short in it that signals your Mac that you have earphones connected. The Mac was engineered so that headphones would override all other audio settings. It is possible that the tip of a 1/8th inch plug is stuck in the headphone jack. Use a flashlight to look inside that port and compare it to the mic port and see if you can identify any foreign material stuck in the port. If you find something, use a paper clip to try and remove it.
Hope that helps,