This is a PCB from a ship. It had burned through the whole thickness of the PCB. It was possible to just add some wires instead of the burned traces but that was not allowed. Besides that, burned PCB is conductive.
I forgot to take a picture from the top that was the most burned and I already cleaned a part of the bottom. But it turned out it was burned through and through.
I milled out all the burned material. A few vias and traces had to go. Not a big problem but if possible (no damage) I spare them.
To show the scale. It was all through hole but that makes it not always more easy. SMD can be more easy because there is no hot component pin burning in the PCB itself.
Making a replacement PCB insert is not difficult but takes some time. Getting it at the right thickness was harder. If there were inner layers I would have made several layers but this was only two sided so I could use one layer. The epoxy for the new traces is the most critical because I need to solder to them. Making and mounting the new vias and new traces is the most difficult part. Because this had to be better as it was, I made much thicker traces. For that I had to mill some PCB material to embed the new trace partly into the PCB so it looks like it was.
This is the result after applying some new green PCB paint. And to protect everything I added some silicon con formal coating. It makes it a bit messy looking but just to be sure. On the picture the coating looks much more visible as it was. All in all this is not that much work but it takes time because things like the epoxy need a few days to hard.