I have a fresh 13.1 install with the following on-board sound card.
00:1f.5 Multimedia audio controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) AC'97 Audio Controller (rev 02) Subsystem: Hewlett-Packard Company d330 uT Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx- Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx- Latency: 0 Interrupt: pin B routed to IRQ 17 Region 0: I/O ports at 1000 [size=256] Region 1: I/O ports at 1400 [size=64] Region 2: Memory at fc800400 (32-bit, non-prefetchable) [size=512] Region 3: Memory at fc800600 (32-bit, non-prefetchable) [size=256] Capabilities:  Power Management version 2 Flags: PMEClk- DSI- D1- D2- AuxCurrent=375mA PME(D0+,D1-,D2-,D3hot+,D3cold+) Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME- Kernel driver in use: snd_intel8x0 Kernel modules: snd_intel8x0
On the original install, I set all channels to 100, tested the sound and all was well.
On normal user login after a reboot, the level of the Master Mono channel had been reset to zero resulting in no sounds on the desktop at all,l from any source.
Using Yast2 sound to reset the Master Mono channel back to 100 restores sound but, after log out and in again, the channel level reverted to zero.
amixer via the cli does not recognise any “mono” control. alsamixer initially shows only one control but F6 and selecting ICH5 shows several including the Master Mono. I can set the level of this channel to 100 but, on exit from alsamixer, no sound is available. Only yast2 sound will actually change things.
On reboot, I did a console log in and looked via yast sound at the card. I saw that the Master Mono channel was set to zero. I changed it to 100, logged out and then logged in as the user via the graphical login screen. yast2 sound now shows the Master Mono channel back to zero!