No sound from headphones - Conexant driver issue?

[UoE]

Incredibly annoying and disruptive problem. Sound from speakers but none from headphones, same when playing system test sounds or media. Have tested headphones with other devices and tried different headphones, have checked master volume.

Headphones are detected when plugged in and appear as the default device in the Sounds window, hotkeys work for volume control and the physical button to mute sound works for speaker output.

This is a clean install of Windows 10 Enterprise v.1803 (build 17134.81) on a ZBook 15u G3. It has an i5-6200U processor and 8GB of RAM. Headphones/jack have worked previously.

Nothing appears to be missing in Device Manager. Have run Windows troubleshooter which seems to update the driver but problem persists.

Performed a driver sweep using HP SoftPaq Download Manager and updated one or two network/storage drivers. Conexant ISST Audio drivers have been updated and rolled back a few times, the Intel Display Audio is the latest version available.

Ran the hardware diagnostics UEFI component test on headphones:-
Product ID: M6G47AV
Failure ID: 60FQ22-00095D-MFGK6K-218B03

As a last  ditch attempt updated BIOS from 01.13 to 01.29 still nothing.  Repeat of UEFI test gives a slightly different failure code:-
Failure ID: 60FQ22-00095D-MFGK6K-218T03

Way too much time and energy has been expended on this but a fix is still desperately required.  

Any help much appreciated.

[UoE · Accepted solution]

Came back to this question which has been bugging me on and off for more than a year now. Posting my solution for completeness, hope it helps someone else.  I have Iost count how many times I have installed drivers (Conexant and Graphics Audio) run troubleshooter etc. but in an unrelated search I just discovered a setting in the BIOS which seems to have worked for me:

Restart > Esc > BIOS setup F10 > Advanced > Built-In Device Options
Check the box for 'Headphone Output'.

Can't say how it came to be unchecked (or why this might be the default after updating BIOS).  Inner peace restored.