Built-in audio after upgrade to Ubuntu 20.04

Good Morning,

I purchased my Precision 7540 back in 2019, with Ubuntu 18.04 LTS factory-installed. Built-in audio (speakers and headphone jack) were working fine. I recently upgraded to 20.04 LTS, and my audio no longer works. The relevant portion of output from 

aplay -l 

is

**** List of PLAYBACK Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: ALC289 Analog [ALC289 Analog]
  Subdevices: 0/1
  Subdevice #0: subdevice #0

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•

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The relevant portion of output from

aplay -L

is 

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•

•

sysdefault:CARD=PCH
    HDA Intel PCH, ALC289 Analog
    Default Audio Device
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•

•

Running 'speaker-test' with root privileges, as

sudo speaker-test -Dsysdefault:PCH -c 2

I *do* get output from the left and right speakers in turn. However, when trying to test speakers from the "Settings" program in gnome, selecting "Analog Output - Built-in Audio" and clicking "Test" gives me no output, and the headphone jack isn't even available to select.

Is there a particular option for 'snd_hda_intel' that maybe I need to specify in  /etc/modprobe.d/alsa-base.conf ? 

Something else obvious I'm missing? 

Thanks,

William