Soundboard cracks

They do appear in the best-regulated environments, but are not a disaster. You make a narrow v-shaped tool out of a small screwdriver and drive it along the crack to remove an even amount of material. Then fashion a corresponding v-shaped sliver of soundboard wood and press it into the gap with a little glue. When dry, you shave it off carefully with a sharp chisel, use a little sandpaper and a cabinet scraper, and then some very dilute shellac to get the colour back. The following two pictures show the two processes, and once the strings are back in place the repairs are hardly visible.