You may want to take a peak in 'alsamixer' in terminal. Worth a shot. Sometimes all that is needed is to "un-mute" the headphones in alsamixer.
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In terminal type
alsamixer
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Hit F6 and choose your AMD card with PCH in the name. It will not be the HDMI.
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You should now see many sliders, including headphones. Make sure this slider is un-muted and turned up.
Worth a shot. Saved me many times.