Regarding the thermistor, if it's not in the older unit (as the parts diagrams indicate is the case) I can't see that its failure accounts for both sets of similar problems. But for the sake of completeness, and because there were some references to possible failed components GRJ mentions, thermistors were explained in a couple of older threads. In each of them scroll down until you get to the posts by SantaFeFan (Jon Z formerly of Lionel who designed the relevant smoke systems):
https://ogrforum.ogaugerr.com/...52#67736898071546452
https://ogrforum.ogaugerr.com/...95#79846750335720495
This might be more info than you need but you never know when the knowledge base can help.
It seems obvious that smoke unit failure can damage the boards but the issue seems to be, what caused the failure? A short somewhere seems likely - just occurs to me to ask if you have got any internal wiring rubbing on a flywheel or otherwise getting frayed?
