Sound on Thinkpad T41 with Fedora Core 4

I have Linux running on an IBM ThinkPad T41 laptop. I recently upgrade from Fedora Core 1 to Fedora Core 4. Several things broke from upgrading, including sound.

A number of people have had sound problems with FC4, requiring various solutions such as disabling the soft modem.

Some people had problems where their mixer settings were muted. Mine was similar. I am familiar with the Linux OSS sound system used in kernel 2.4, but I am unfamiliar with the ALSA sound system used in kernel 2.6.

I verified that my sound hardware was detected, using various utilities like system-config-soundcard, lspci, and lsmod. Under KDE, I used kmix to set the volume and unmute the sound channels. The artscontrol display showed me that all of the software believed it was pumping sound to the soundcard when playing a song in xmms. It was starting to look to me like my hardware and sound module setting were good, but I was somehow muted.

I discovered that in addition to volume levels and mute settings for input and output in the sound mixer, ALSA also has some additional on/off switch settings. I do not recall seeing these with the earlier OSS sound drivers. In the case of this T41 laptop, I found a mixer switch called "Headphone Jack Sense". Turning this off gave me working sound immediately.