There are basically 2 chambers in the aristo unit, the one on the left has the fan in it, and the one on the right has the fluid reservoir. The wall between them is cut down a bit at the top, so the air goes from the left to the right:
Here's the circuit board that fits down into the housing shown above. You see the exhaust opening on the right side:
You can also see the wick underneath, that sits into the reservoir.
The picture below shows the problem, the circuit components are exposed to the smoke vapor, and even though the flow of the vapor is mostly out the hole under the heating element, the vapor contacts everything, condenses on the circuit board, and affects the components on the board.
The components that most often fail are the 3 electrolytic caps, you see 2 on the right end of the boards, and there is one just peeking out behind the motor. The large black device to the left of the motor is an inductor.
The caps are soldered tight to the board, and the smoke fluid expands the rubber sealing at that end of the cap, and breaks them away from the board, normally damaging the copper traces.
Thats the Aristo smoke unit in a nutshell. There's some other weak points that explain units that run for 5 minutes and quit, but I'm SURE I will be accused of bashing by now, so visit my web site page:
http://www.elmassian.com/trains-mainmenu-27/motive-power-mods-aamp-tips-mainmenu-35/aristo-motive-power-mainmenu-72/aristo-smoke-units
The TAS and MTH units do not have this weakness.
Regards, Greg