Yamaha Pss 560: I killed it?

[zorgitron]

Hello all!
I have a pss 560 that I added a delay effector ( pt2399), and an input mixer to. It also could run off a usb phone charger backup battery. It was awesome! I could plug in a poly 800 and jam without an amp with nice synthy delay effects.

It suddenly started making a deep buzzing sound, and after a minute or so, stopped everything. Now, only the pilot turns on. You might say its "dead" or "bricked" I suppose.  But I'm a stubborn bastard and I want my cool jam station  back!

The 560 is nice since there are free schematics for it online. I used them to pinpoint where to run the signal into the delay circuit. Simply, it ran into the power amplifier, along with an input signal. The usb power was just a usb plug wired in the same way as the battery wires.

Im suspecting that a wire came loose and shorted something important.
t. Before it died, I played the keyboard and noticed the delay wasnt working, so maybe a wire dropped off. Then it started working again. Also it happened after I plugged in a 12v psu by mistake ( i had another pss next to it, mistaken identity)
Can anyone give me so pointers to trace the problem? I checked many of the big ICs amd they are still getting their 5v, but after that, not sure what to look for. Thank you and glad to finally join one of these groups !