WHAT WOULD CAUSE JC-1 MONOBLOCK TO SELF DESTRUCT?

Hi all,
I own Parasound Halo JC-1 monoblock amps, and have never had any reliability issues at all with them.
I have a friend, however, who had a JC-1 monoblock to literally self-destruct.
He said he was listening to it at normal levels, and heard a loud pop that almost sounded like a firecracker went off, the amp went completely dead, and the smell of toasted components filled the air.
He shined a flashlight through the top cover and said that it looked like at least 8 to 10 of the black square Sanken transistors mounted on the sides of inside of the amp, on the heat sinks, had literally blown to pieces!
He said the Sanken devices were still there, but the centers of many of them had literally blown out.
I would assume that these square black Sanken devices are the output transistors?
He checked the power cord, speaker cables, speakers, interconnects, etc., for short circuits and found nothing!
Has anyone else out there had this to happen to their Parasound Halo JC-1 monos, or any other amp before?
What would cause such an incident to happen?
Any answers, ideas, or help would be greatly appreciated.
Thanks a million!
Angela