Here's the parts page for this locomotive: Lionel 6-48084 UP Challenger Parts. As you can see, it uses the standard AC regulator module. I'd seriously consider taking it to a qualified tech for repair.
The fact that the PCB has been cooked leads me to believe that the resistor may have shorted to the smoke unit fluid chamber, you have to make SURE it doesn't touch the sides of the bowl.
If you are bent on repairing it yourself, you probably need at least these two parts, and I'd also replace the smoke resistor with the 8 ohm one.
