The first warning sign should've been when I accidentally snapped off the locking clips, while trying to open the cube.
No worries though. A touch of glue should make accommodation to that. My careful planning would not be derailed so easily!
I quickly found, and removed, the damaged circuit board. The replacement wasn't identical, but by mounting it on the opposite side, and replacing the transformer to increment the voltage slightly, I was sure it would work.
I plugged it into the wall and turned it on... then watched in horror as my prized possession melted into an unrecognisable lump.