Power supplies or amplifiers can easily become overloaded due to the heavy current loads they carry. This can cause a short in one or more of the electronic components, causing it to burn and give off an acrid odour. In some cases the circuit board that holds the components burns, causing the board and the copper tracks on the board to burn. If only one or two components are destroyed and the area burnt on the board is one inch square or less, then it is viable to repair the board.
Visually assess the board to decide if it is worth repairing. If it is, remove the board from the faulty electronic apparatus. This may mean unsoldering some wires or unplugging connectors. Make a note of where the wires were connected to make reassembly easier.
Remove electronic components in the burnt out area using a hot soldering iron. Heat each leg of the component until the solder holding it to the board softens, allowing the leg to be removed. Dip a stiff brush in isopropyl alcohol and brush the burnt area on both sides of the board to remove as much of the char from the board as possible.
Check for breaks in the copper tracks on the burnt area of the circuit board. If a break is noted, drill a small hole in the copper track on each side of the break. With small pliers cut off a small piece of wire and bend the ends to form a staple. Push the staple down into the holes from the top side of the board, taking care not to lift the copper track away from the board.
Using the soldering iron to heat the ends of the staple and copper track on the underside of the board while applying solder. Apply only enough to form a small solder mound around the ends of the staple and the copper track. Check the solder joint using a magnifying glass to ascertain there are no cracks between the solder joint and the staple ends.
Continue these steps for any other breaks in the copper track on the board. Brush off the rosin left on the board from the solder using a brush dipped in isopropyl alcohol. Clean the eyelets (holes) where the component legs were soldered to the board. Solder new electronic components back onto the board. Reinstall the board.
Components and equipment can be obtained from an electronic shop.
Caution should be taken when working with a soldering iron to avoid severe burns.