need help identifying a part on kac-9104d

[usmcgrunt0331]

my amp is stuck in protection mode so i opened her up to find this [IMGDEAD]http://i55.tinypic.com/t9bltt.jpg[/IMGDEAD]

wtf is that thing?

 

[Iain McNeill]

That is the invitation to a lifetime of tweaking.
A blown tranny shorting the rails.

Replacing the transistor probably won't repair the amp. You need to find out why the transistor shorted. Not for the faint of heart. Have you done this before?