The Littlest Meap

Disabling a Mac Book Pro’s Optical Out

Posted by: meaplet on: July 31, 2008

A couple of days ago the headphone jack on my MacBook Pro started to glow an eerie red, and my internal speakers stopped working. Below, I’ve provided a brief explanation of what happened, and the steps I followed to resolve the problem. Apparently it’s a common issue on MBPs.

Clever folks that they are, the Apple folks designed the headphone jack on MBPs to take both standard headphones and digital audio out. It detects which jack is plugged in by the shape (differently-shaped jacks trigger different switches inside the port) and automatically disables the internal speakers when an external audio out device is plugged in.

The problem with this design turns out to be the switches inside the port. Because they’re apparently entirely mechanical, once a switch has been triggered by plugging a device in, it doesn’t release control of audio to the default speakers until it’s been triggered off. And, it turns out, if you unplug your standard headphones at the wrong angle, it’s possible to toggle on the digital out. The digital out is transmitted by an optical signal, hence the red light from the headphone jack.

Fascinatingly, plugging in a different audio device (aka, headphones) overrides the digital out, but only until that device is unplugged, at which point the digital out takes control once again.

So how do you resolve the situation? Manually.

Take a toothpick or another small hard, non-metal object, and trigger the digital-out switch, which is in approximately the 6-7 o’clock position in the port. Metal objects don’t seem to cause any damage, but when I tried using screwdrivers to trigger the switch, the port detected them as headphones and turned off the digital out only when the screwdriver was in the port. A toothpick did the trick within seconds.

8 Responses to "Disabling a Mac Book Pro’s Optical Out"


If I say that it’s germanically over-engineered, does that suggest what I mean? Seriously, that’s just *foolish design*.

I’m totally with you there. Ludicrous move on Apple’s part, especially as I’ve yet to see a digital speaker that would use the port. (And it still doesn’t handle standard speaker cables, which I feel would be more common…)

This issue can be fixed if you MBP is still under warranty The Guys at the Genius Bar will take your MBP for a few days and swap out its Left I/O board for a new one.

Thank you, that solved a great mystery for me and worked too!
Have added a toothpick to my essential computing tool box.

Happy it worked for you, John! I haven’t had the problem since, although the friend who told me how to fix it had had it happen to her laptop repeatedly.

Thanks so much for sharing your fix – worked like a charm!

Oh my gosh, thank you! I plugged in iPhone headphones and the red light in the jack came on and disabled my speakers. I just stuck a wooden match stick in and disabled the optical out. My Applecare just ran out less than a month ago too. Thanks again.

Thank you very much! I had the same problem and after having read your article and doing what you wrote, it works good! Thanks :)

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