Macbook Air mid 2013 (My beloved)
Lost all sound about 6 months ago. Tried all the methods mentioned on previous 24 pages, all no no avail, with no installed audio hardware reported, it appeared to be a logic board problem.
Bluetooth speakers worked OK but sometimes a bit scratchy to the Speakers. BT headphones from my phone did not connect. HDMI to TV via Thunderbolt adaptor also worked with 5m cable across the floor to the TV.
Put up with this for 6 months, not worth $600-odd to repair with no real warranty of enduring success.
So just a week before Xmas I bought myself a Lenovo laptop that looks a lot like the new gold macbook. Thin/skinny, 2 C - ports plus 1 USB3 as light as the air, same size, converts to a tablet. Decided I had to learn Windows instead. Still have a house full of macs to replace as they fade.
BUT YESTERDAY A BIG NEW SYSTEM UPDATE INSTALLED (=10.12.2 (16C67), and audio is 100% normal now. Now I have 2 small similar competing laptops, and will have to carry on as planned, and learn Windows instead. Cannot depend on the macbook series any more after 6 months of no sound, so will probably retire all the macs as they fall over with time. Will be a sad but inevitable day sometime in the future.
So advice for now is get the OS update 10.12.2 (16C67) before you decide to replace the old Macbook.