That is a 3A surface mount diode, from memory the reverse-polarity protection one, which is easily replaced. The possible problem is that you can seen just below and to the left of the diode package what looks like a burned-out track, probably on an internal power layer which has scorched the upper layer of the PCB. It's repairable, but may need a patch wire.

pca
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Experience is what you get just after it would have helped...