[4383, Conexant CX20590, Speaker, Internal] Playback problem

[Solebanana]

Left internal speaker works. Right doesn't. Tried the usual fixes, see for example https://itsfoss.com/fix-sound-ubuntu-1304-quick-tip/. In particular, no sign of anything being muted or turned down on a mixer. Headphones work OK. I gather this 'one speaker' (usually the right) 'doesn't work but headphones are OK' issue has been seen before on various Ubuntu builds. I'm on 20.04 having recently upgraded.

Ubuntu is running from a USB stick. The hard disk has Windows 10 on it, and that works; from which I conclude that this isn't a hardware fault. I can't find any reference to a proprietary driver being required; as far as I understood it the thinking seemed to be that with a sufficient kernel this hardware should work on Linux with no problems.

I only really stumbled across this kind of by accident, so I don't know how long this machine has had the bug on it. I have a vague recollection from ages ago of having noticed it before.

You probably have all this from the automated probe, however... (see below)
I'm a bit puzzled about the references to rear speakers. There's one each side as I understand it, though I can't actually see the things and there appear to be some references to some G575s only having one speaker. This spec seems to say two:
https://www.cnet.com/products/lenovo-essential-g575/
and so does this one:
https://laptops-specs.blogspot.com/2011/06/lenovo-g575-specs.html

I'd be quite happy with the speakers playing mono from the left side if that was possible, as long as the headphones were still stereo.

Description: Ubuntu 20.04.1 LTS
Release: 20.04

System:
  Host: Ubuntu-SanDisk Kernel: 5.4.0-52-generic x86_64 bits: 64
  Console: tty 0 Distro: Ubuntu 20.04.1 LTS (Focal Fossa)
Machine:
  Type: Laptop System: LENOVO product: 4383 v: Lenovo G575
  serial: 2780751900857
  Mobo: LENOVO model: Inagua serial: CB11824372 BIOS: LENOVO
  v: 41CN26WW(V2.02) date: 09/14/2011
Audio:
  Device-1: AMD SBx00 Azalia driver: snd_hda_intel
  Sound Server: ALSA v: k5.4.0-52-generic

amixer version 1.2.2

default
    Playback/recording through the PulseAudio sound server
surround21
    2.1 Surround output to Front and Subwoofer speakers
surround40
    4.0 Surround output to Front and Rear speakers
surround41
    4.1 Surround output to Front, Rear and Subwoofer speakers
surround50
    5.0 Surround output to Front, Center and Rear speakers
surround51
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71
    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
null
    Discard all samples (playback) or generate zero samples (capture)
samplerate
    Rate Converter Plugin Using Samplerate Library
speexrate
    Rate Converter Plugin Using Speex Resampler
jack
    JACK Audio Connection Kit
oss
    Open Sound System
pulse
    PulseAudio Sound Server
upmix
    Plugin for channel upmix (4,6,8)
vdownmix
    Plugin for channel downmix (stereo) with a simple spacialization
sysdefault:CARD=SB
    HDA ATI SB, CX20590 Analog
    Default Audio Device
front:CARD=SB,DEV=0
    HDA ATI SB, CX20590 Analog
    Front speakers
surround21:CARD=SB,DEV=0
    HDA ATI SB, CX20590 Analog
    2.1 Surround output to Front and Subwoofer speakers
surround40:CARD=SB,DEV=0
    HDA ATI SB, CX20590 Analog
    4.0 Surround output to Front and Rear speakers
surround41:CARD=SB,DEV=0
    HDA ATI SB, CX20590 Analog
    4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=SB,DEV=0
    HDA ATI SB, CX20590 Analog
    5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=SB,DEV=0
    HDA ATI SB, CX20590 Analog
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=SB,DEV=0
    HDA ATI SB, CX20590 Analog
    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
dmix:CARD=SB,DEV=0
    HDA ATI SB, CX20590 Analog
    Direct sample mixing device
dsnoop:CARD=SB,DEV=0
    HDA ATI SB, CX20590 Analog
    Direct sample snooping device
hw:CARD=SB,DEV=0
    HDA ATI SB, CX20590 Analog
    Direct hardware device without any conversions
plughw:CARD=SB,DEV=0
    HDA ATI SB, CX20590 Analog
    Hardware device with all software conversions
usbstream:CARD=SB
    HDA ATI SB
    USB Stream Output

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: alsa-base 1.0.25+dfsg-0ubuntu5
ProcVersionSignature: Ubuntu 5.4.0-52.57-generic 5.4.65
Uname: Linux 5.4.0-52-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.10
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: michael 1697 F.... pulseaudio
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Sun Oct 25 16:27:27 2020
InstallationDate: Installed on 2017-03-08 (1326 days ago)
InstallationMedia: Ubuntu 16.04.2 LTS "Xenial Xerus" - Release amd64 (20170215.2)
PackageArchitecture: all
SourcePackage: alsa-driver
Symptom: audio
Symptom_AlsaPlaybackTest: ALSA playback test through plughw:SB failed
Symptom_Card: Built-in Audio - HDA ATI SB
Symptom_Jack: Speaker, Internal
Symptom_Type: Only some of outputs are working
Title: [4383, Conexant CX20590, Speaker, Internal] Playback problem
UpgradeStatus: Upgraded to focal on 2020-10-18 (6 days ago)
dmi.bios.date: 09/14/2011
dmi.bios.vendor: LENOVO
dmi.bios.version: 41CN26WW(V2.02)
dmi.board.asset.tag: Base Board Asset Tag
dmi.board.name: Inagua
dmi.board.vendor: LENOVO
dmi.board.version: Base Board Version
dmi.chassis.asset.tag: Chassis Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: Chassis Manufacturer
dmi.chassis.version: Chassis Version
dmi.modalias: dmi:bvnLENOVO:bvr41CN26WW(V2.02):bd09/14/2011:svnLENOVO:pn4383:pvrLenovoG575:rvnLENOVO:rnInagua:rvrBaseBoardVersion:cvnChassisManufacturer:ct10:cvrChassisVersion:
dmi.product.family: IDEAPAD
dmi.product.name: 4383
dmi.product.sku: 123456789
dmi.product.version: Lenovo G575
dmi.sys.vendor: LENOVO

[Solebanana (solebanana)]

I have new information about this issue.

I went back to Windows to retest (I'm typing on it now). The same thing happens as on Ubuntu - only left channel output comes out. I notice that it actually comes out on the right of the laptop. Anything that should come out of the right speaker doesn't get heard at all. Even Windows sound configuration speaker test can't work the right speaker.

The likeliest explanation appears to be that despite the specs, this specific G575 only has one speaker, which is mounted in the right hand side of the case but is recognised by software as the left speaker (possibly because it's the first one).

Therefore what I really need is a way of getting Ubuntu/Alsa to treat internal speaker sound as mono and have both channels come out of the one and only speaker.

Sorry for the confusion.