Ouch!
I haven’t looked, but if the model has been approved by the (US) FCC, the computer’s label will have an FCC ID. You can use that ID to look up the description at the FCC site. That usually includes some kind of circuit schematic.
I don’t think that it will be easy to repair (but I’m no expert):
- it looks as if two discrete SMT components were badly fried. I would guess that they were part of the power supply
- the board itself may be damaged: this board is surely multi-layer and it is possible to burn the interior layers
- the first picture hints at damage to the chip above the worst spot. Some other nearby spots look as if thy might be damaged. That may just be the way the photo came out.
- chips that look OK can be damaged by such an event
The fact that it wasn’t plugged in is interesting. Notice the silk-screened lettering “BAT” near the burn’t area. That probably stands for “battery”.
I wonder if you can find someone with Cube Mix Plus with, say, a cracked screen and buy their computer for parts? I’d bet that a cracked screen is the most common death of these computers.