Ubuntu 12.04 - No sound on laptop speakers

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http://askubuntu.com – Computer: Acer Aspire 6920 Card: HDA Intel Chip: Realtek ALC889 My problem is that the laptop build-in speakers don't play any sound. When i plug in my headphones the sound works normally, the same goes with external speakers. Those work normally like the headphones. The profile in the Sound settings is Analog two-way Stereo. I am using Ubuntu 12.04. Might trere be any problem with my sound drivers or something similar? Any form of help appreciated. (HowTos)