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Possible Duplicate:
Optical Audio out stuck on on a MacBook

When I plug my headphones into my iMac (27-inch, Mid 2011; OSX 10.8.1) and try to adjust the volume, the volume popup shows a greyed out speaker and there's a circle with a line through it signalling that it isn't working.

I've tried the headphones with my iPhone, other iMacs etc and they're fine. This is incredibly frustrating. Other headphones don't generally work either.

In Sound preferences the headphones are being listed as "Optical digital-out port" which is incorrect and would explain the problem, but doesn't help me fix it.

Any ideas?

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marked as duplicate by Sathya Sep 11 '12 at 9:34

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

Do you see any red light shining from around the headphone jack by any chance? I suspect the optical-digital output is being activated (there is a switch detecting the jack length, IIRC). – Martijn Pieters Sep 11 '12 at 8:28
@MartijnPieters I can't see any, but which I click on Sound preferences it does say "Optical digital-out port" which it shouldn't. – Alex Coady Sep 11 '12 at 8:32

Your headphone output jack has a microswitch that's supposed to detect when you insert a special optical connector. Sometimes however this switch gets stuck and your computer will not play audio through your attached headphones even when you plug them in.

The trick that has always worked for me is to take a toothpick, insert the slot and swipe it around the inside. That normally dislodges the switch.

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