How to switch between headphones and speakers manually

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http://askubuntu.com – I have an Asus G60JX laptop with Ubuntu 12.04 installed. The laptop has the sound jack broken (the jack thinks that there are always headphones plugged in, even though there is nothing. so i can hear the laptop with headphones, but when i unplug them the internal speakers are silent.) Is there a way to switch between internal speakers and headphones manually? (HowTos)