It's easy to see if the chuff switch is actually working, with no power on, just check the switch with a meter while you rotate the flywheel. I suspect after three times you're pretty good at replacing that switch.
You do know that insanity is doing the same thing multiple times and expecting a different result, right?
The common element in that locomotive is the Smoke Fan Control PCB, that's more likely where the problem lies. Obviously, checking the integrity of the wiring is key before replacing components.