No sound on headphones attached to front panel

In Debian Stretch the auto-mute function is not working as expected. In case there's no sound on headphones attached to the front panel of a linux machine, disable auto-mute as follows:

• Run the command alsamixer in the terminal

• Press "F6"
• Select the on-board sound card named "0 HDA Intel PCH"
• With the arrow (cursor) keys move to the slider labelled "Auto-Mute"
• Disable auto-mute by pressing the "arrow down" key
• Plug-in your headphones
• Make sure the sliders "Master" and "Headphone" are unmuted by pressing "m"
• Set the volume of the sliders "Master" and "Headphone" with the arrow up/down keys according to your needs