I'm 100% sure it's the PCB. You can see the burns on it near the power connector. That's not to say the internals aren't cooked too, I've got two here from a customer where both had blown PCBs and blown heads from wrong voltage connection. But, in any event you'll need to start by replacing the PCB.
You need to match the PCB number which is printed in the green material of the back side of the board. It should be a number like "100535704 REV C". Once you track down a PCB with that same number (doesn't matter what model drive it comes from) you'll need to transfer the 8 pin ROM chip from your original PCB to the new one. I've circled the chip here:

- rom.jpg (177.04 KiB) Viewed 5339 times
Just remember that if you overheat and destroy the chip it's going to be a rough and expensive recovery. So if the data is really important, it might be best to let a professional handle it.