Harman Kardon HK6500 Audio amp repair (huge output with no input)

[Jadon]

I've got a Harman Kardon HK6500 Amplifier that was working fine about 5 years ago and then put into storage as we ha no use for it. The other day I got it out and plugged it in with a bookshelf speaker of mine connected, and in about 5 seconds it fried it completely. There was a slight hum, and while turning up the volume on the amplifier to see if I could hear the music, I just heard sizzling from the speaker. (Its beyond fried, was perfectly fine before this operation).

I put the amplifier output on my scope with no input connected and volume at 0, as well as with an input and varying the volume and its putting out a 102V peak to peak waveform no matter what I do!!!!
The frequency is <1Hz, and a weird shape but consistent. I have no idea where to start, nothing is getting hot, no fried components (that I can see), and no immense power draw.

Any ideas on where to go next?