Diode 102-105 are conducting when + and - 12Volt is reversed.
In example below it results in a short between between -12Volt to +12Volt through Diode D104 and D105
When the powersupply shuts off only one 12V rail (due to overload) , the speaker is continuous powered by 12Volt (+ or -) relative to GND. Also capacitors C116 or 119 is wrong polarized this way.
I think that the opamps are relative safe behind the 7x05 regulators.
It's a little guess what really happened and whether or not the (+) and (-) 12Volt stayed active all the time.
Inspect capacitors C116,119,109,112 and diode D102-105.
