Read through cheaper 9 of this book. You'll find most of your answers there. It's likely you need to replace the opto coupler.
What version of AB do you have? CP1 should be available from any major electronics dealer.
For sound my CII originally had scratchy sound then lost it all together. After recapping the AB and I think desoldering the sound chip and cleaning and putting it back on it stared working fine. One of the caps on the logic board directly affects the sound. If you pull that trace and don't repair it will have issues as well.
ASC - too many Macs have ASC's left and right channels blended into mono for for driving the internal speaker. For one, it's a massive PITA to get get past that kluge to wring stereo of out of a Duo/DuoDock even tweaking system and driver for coaxing the PAS16 NuBus card to do the trick! ASC is a large enough package to do the likes of the Portable's kluge chip with modern logic, providing headers or a connector for a daughtercard if necessary for implementing internal stereo in any number of Macs and the likes of the PowerBook 1400c. Dunno if anyone would really be interested in doing something with such a thing when I guess you could hotwire to a line level stereo headphone jack, but it would be neat play with at board or daughtercard level.
On second thought, adding headers to a new logic board design for making the internal headphone jack connection might be a plan. Dunno, ASC/Sound limitations were the first thing that popped into my head when you asked for suggestions.