I've replaced burned out PCB's a few times on critical data drives, but it requires finding another drive of the exact same model and if possible nearly the exact same production year and month and sacrificing it. Once the PCB is swapped out and the drive is accessible, get the data of of it immediately. I normally use Ghost to clone the drive and then wipe it before disposing of the previously failed drive.
If anything else goes wrong with a drive I'd either just toss it or send it to a data recovery professional. As has been stated before, opening the case requires a clean room.