Sony xplod xm-554zr amp

Hey my sony xplod xm-554zr amp died on me and i pulled it apart to check it out and see what the deal was and when i put my omp meter across two legs of one of the transistors it gave me a reading which im pretty sure its not. They shudld be conected at all( none of the others do this). Now I thought it would be simple you know go down to the local electronics store buy one and install. Well no its not i cant find which one to buy the transistor has the following writen on it:

 K
B778
0 628

I live in New zealand and my local dont have one so what do these letters mean and what do i buy to replace it? Im asuming that it cant be 2 expensive but if anyone can help on what this transistor is or where to buy 1 from nz this would be much apreciated

Thanks