The insulation of some whiring is damaged and caused a short circuit, causing some plastic, probably the insulation, to burn. Melted plastic don't smell, burning plastic DOES smell.
The whole whiring must be checked and any damaged whire replaced.
Depending on exactly where the problem occured, some other component could be damaged. In this case, a damaged component will display some burning marks, not just some melted plastic. With some luck, the damage will be only cosmetic and limited to the casing.
Electro, February 2013
