Headphones no audio output at all

Went to use headphones for the first time and got no audio output. I use Ubuntu on an iMac and the speakers work ok and the headphones work when in osx.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: alsa-base 1.0.25+dfsg-0ubuntu5
ProcVersionSignature: Ubuntu 4.13.0-36.40~16.04.1-generic 4.13.13
Uname: Linux 4.13.0-36-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.15
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/pcmC0D0c: brent 2112 F...m pulseaudio
 /dev/snd/controlC0: brent 2112 F.... pulseaudio
 /dev/snd/controlC1: brent 2112 F.... pulseaudio
CurrentDesktop: Unity
Date: Sun Mar 11 18:20:29 2018
InstallationDate: Installed on 2018-03-07 (3 days ago)
InstallationMedia: Ubuntu 16.04.4 LTS "Xenial Xerus" - Release amd64 (20180228)
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/pcmC0D0c: brent 2112 F...m pulseaudio
 /dev/snd/controlC0: brent 2112 F.... pulseaudio
 /dev/snd/controlC1: brent 2112 F.... pulseaudio
Symptom_Jack: Green Headphone Out, N/A
Symptom_Type: No sound at all
Title: [iMac12,1, Cirrus Logic CS4206, Green Headphone Out, N/A] No sound at all
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 08/08/17
dmi.bios.vendor: Apple Inc.
dmi.bios.version: IM121.88Z.004D.B00.1708080012
dmi.board.name: Mac-942B5BF58194151B
dmi.board.vendor: Apple Inc.
dmi.chassis.type: 13
dmi.chassis.vendor: Apple Inc.
dmi.chassis.version: Mac-942B5BF58194151B
dmi.modalias: dmi:bvnAppleInc.:bvrIM121.88Z.004D.B00.1708080012:bd08/08/17:svnAppleInc.:pniMac12,1:pvr1.0:rvnAppleInc.:rnMac-942B5BF58194151B:rvr:cvnAppleInc.:ct13:cvrMac-942B5BF58194151B:
dmi.product.family: iMac
dmi.product.name: iMac12,1
dmi.product.version: 1.0
dmi.sys.vendor: Apple Inc.