Comment 13 for bug 1672822

@rotten hdajackretask worked for me. Confirmed.

My Acer Predator 15 G9-593-72VT has:
Card: HDA Intel PCH
Chip: Realtek ALC255

FIXING IT BY SETTING THE PINS AKA JACK RETASKING:

STEP 1: INSTALL THE FOLLOWING SUITE OF APPS:
sudo apt-get install alsa-tools-gui

STEP 2: RUN THIS PARTICULAR APP FROM THE SUITE AT THE TERMINAL:
hdajackretask

STEP 3: CHECK THE FOLLOWING BOX:
show unconnected pins

STEP 4: SET THE PINS AS FOLLOWS:
0x14 to "Internal Speaker" (do NOT check the box for override)
0x17 to "Internal Speaker LFE" (check the box for override)
0x1b to "Internal Speaker (Back)" (check the box for override)

STEP 5: TEST IT
(play a song or stream a video?)

STEP 6: IF THE TEST SUCCEEDS, CLICK BUTTON:
Install Boot Override
(you will need to put in an admin password)

STEP 7: REBOOT
See if the settings stuck after a restart.

At any time, if something goes wonky, restart the computer, and try again. I found that sometimes the sound quits and freezes while applying different configs, but a restart resets it back to normal.

https://i.imgur.com/B6iYgcN.jpg