I see two diodes. The one on the left shows a "3". The one on the right shows a "4" and another "4". Can you remove one of those to see any hidden numbers? If it is an IN4403, that is a Zener diode. I would think the two diodes are the same.
As for the trace with the green coating removed - that might not be a big deal. Use your ohmmeter to see of you have continuity from one solder joint to the next. There have been many times when I use an Exacto Knife to remove some green coating when I am flowing solder onto a trace. It helps add to a stronger joint.
This amp might be a tough one to find a schematic.