Resolving issue with sound not coming out of speakers but working fine with headphones
Curiously this issue occured after I re thermal pasted my laptop. Somehow the BIOS was reset even though I don't recall disconnecting the CMOS battery.
Anyhow, after many days/weeks of investigation incuding replacing the speakers, I discovered the PCM volume was set to 0. I
even tried adding entries into the /boot/device.hints file. I eventually discovered the issue
though a handy console utility call mixertui. It gives you an old school console graphical display of the volume
which allows you to easily increase the volume of the pcm channel. Problem solved.
A couple of good threads to read if you are having a similar issue and that doesn't help. The second was where I found the above utility.