Hmm.... I have a dead 3640 card. (From my backup A4000) I never bothered to try to track down the cause of death. Maybe it's an easy one. I'll check it out. Thanks for the info!
It's also good to know what causes A4000s to lose sound. It's not a problem mine has, but I know they are prone to it. (I always just assumed it was caused by people mixing sound output by splicing wires together. ;-) )