Q: macbook air early 2015 inbuilt speaker sound went off on sleep

My macbook air early 2015 inbuilt speaker sound went off on sleep and never came back

(since 3 days I am trying everything using online forums, my laptop 1 year support is over)

Few points to be noted

  • In external headphone is working when I plugin.

  • System Preferences > Sound > Output > (Internal Speakers : Built-in) is selected correctly. No other option available. Mute is not selected.

  • There is no red mark error, notifying about service. and since the external headphone is working, I believe sound card is working fine.

Few things which I tried

  1 PRAM reset. http://support.apple.com/kb/PH14222

  2 SMC reset. http://support.apple.com/kb/HT3964

  3 Tried plugin plug out 3.5mm headphone jack multiple times.

  4 Uninstalled all other softwares which was not provided by default OS.

  5 Downloaded latest OS X using AppStore>Purchased>latest OSX El Captain 10.11.6, and reinstalled.

  6 Killed process coreaudiod using terminal / Activity monitor and restarted laptop.

  7 checked in Application > Utilities > Audio midi Setup.

All the above didn't worked for me.

Other details

macbook air Early 2015, 13inch, 4GB RAM, 1.6Gz intel i5, inbuilt battery

original OS X provided with macbook air :  Yosemite , current OS X : El Captain 10.11.6

Can anybody help me understand whether its an software problem,

and if its a software problem, when a new El captain upgrade will come, then will the inbuilt speaker sound will automatically start working ?

Shall I try and external bootable OS X install by deleting all system HDD data by formatting ?

Or its an hardware issue which can only be solved using hardware service ?

(if anyone want me to attach screenshot, I will do that)