Here's an alternative that worked for me on a Manjaro 18 system.
Under 'Black Headphone, Left side' Pin ID:0x21, select the Override check box.
In the drop down list, select Internal Speaker
Click on Install Boot Override
Sound works great on external speaker when plugged in to Headphone jack, internal speakers work when externals unplugged.
I still can't figure out why there is no sound on the internal speakers on my HP 27wm monitor, connected with HDMI cable to the laptop, but after 2+ weeks of searching and experimenting, it's good to have my external speakers working again.