No sound when connecting headphones or external speakers to my laptop [TravelMate P648-M, Intel Skylake HDMI, Digital Out, HDMI] No sound at all

[Miquel]

The sound works fine except when I connect either speakers or headphones (stereo jack) to my laptop, then there is no sound. When I disconnect them it sounds normal. I checked the alsamixer, no channel is muted. The system doesn't seem to notice that I have plugged something in, since the sound settings "output" does not change to "speakers" or similar (as it did in my old computer).

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: alsa-base 1.0.25+dfsg-0ubuntu5
ProcVersionSignature: Ubuntu 4.4.0-112.135-generic 4.4.98
Uname: Linux 4.4.0-112-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.15
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: banchsm 1679 F.... pulseaudio
CurrentDesktop: Unity
Date: Sun Feb 4 15:04:14 2018
InstallationDate: Installed on 2017-07-20 (199 days ago)
InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
PackageArchitecture: all
SourcePackage: alsa-driver
Symptom: audio
Symptom_AlsaPlaybackTest: ALSA playback test through plughw:PCH failed
Symptom_Card: Built-in Audio - HDA Intel PCH
Symptom_DevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/pcmC0D0p: banchsm 1679 F...m pulseaudio
 /dev/snd/controlC0: banchsm 1679 F.... pulseaudio
Symptom_Jack: Digital Out, HDMI
Symptom_Type: No sound at all
Title: [TravelMate P648-M, Intel Skylake HDMI, Digital Out, HDMI] No sound at all
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 07/22/2016
dmi.bios.vendor: Insyde Corp.
dmi.bios.version: V1.13
dmi.board.asset.tag: Type2 - Board Asset Tag
dmi.board.name: BAD40_SL
dmi.board.vendor: Acer
dmi.board.version: V1.13
dmi.chassis.type: 10
dmi.chassis.vendor: Acer
dmi.chassis.version: V1.13
dmi.modalias: dmi:bvnInsydeCorp.:bvrV1.13:bd07/22/2016:svnAcer:pnTravelMateP648-M:pvrV1.13:rvnAcer:rnBAD40_SL:rvrV1.13:cvnAcer:ct10:cvrV1.13:
dmi.product.name: TravelMate P648-M
dmi.product.version: V1.13
dmi.sys.vendor: Acer