Before unsoldering defect components cut the leads first, remove the component body, then unsolder the leads. This way you need less heat and it protects the lands. When replacing D1 or R1, don't seat the component on the board, leave a couple of milimetres of air space. This will help to prevent charring of the PCB (printed circuit board). With R1 raised from the board there is enough space to fit a ¼ watt resistor, this gives better heat dissipation, it will also take more of a beating before it burns out. If the PCB has suffered from burn damage it's important to remove the charred area, the charring is carbon and carbon is a conductor. This can lead to further damage to the board and possible problems with the rest of the circuitry, or even an outbreak of fire. See attached photos. If a large or deep area of the board is removed because of charring it can be filled with epoxy resin adhesive, after all the PCB is of epoxy resin/fibre glass construction. It also pays to have a fine drill and pin vice on hand to ream out mounting holes and clearing surplus solder from the reverse side. In the first photo you can see the damage caused by a burned out D1 diode. In the second photo the light has been set so the depth of the damage can be seen.
posted on: 20/01/2015 00:33:50