Catastrophic failure on Mixing Console PCBs, anyone ever seen this?

Hey everyone,

I am working on repairing some PCBs off of a TL Audio VTC Mixing Console. There seem to be multiple points of failure, but I have never seen damage this catastrophic and I am wondering anyone has any ideas about what caused this level of damage.

The first damaged item was an LM339N OP-AMP, which ended up actually destroying the pad connected to pin 12, which is GND. Of all the pins, why would GND be burnt up? This device is part of the VU-Meter circuit was is essentially a peak detector circuit for the volume level.

The next failure point was on another PCB in the same console, located nowhere near the previous one. This seems to have melted on both sides somehow. There was also a ribbon cable underneath the board which melted.

I actually managed to find the schematic for the second board, and it seems to be part of a switching circuit for the Pre-Fade-Listen audio signals. It seems like this IC was responsible for the left channel, because the IC2 is actually responsible for the right channel and it is completely fine.

Strangely enough, the analog switch ICs are fine, it is just the OP-AMPs that are destroyed...

If anyone has seen anything like this before it would be really helpful!