I would replace the entire circuit board. Carbon arcs have a tendency to create more arcing in the future. This is not a good thing.
I would NOT use the amp until the board is replaced. JMO
"If someone tells you he believes in and talks to an invisible bunny named Harvey, you put him on medication and a regimen of therapy. If someone tells you he believes in and talks to God, well, that's perfectly acceptable. Why that's the case is impossible for me to fathom." - WP2XX
"He's dead, Jim. You take his Tricorder and I'll get his wallet."
"The problem with America is stupidity. I'm not saying there should be a capital punishment for stupidity, but why don't we just take the safety labels off of everything and let the problem solve itself?"