No, it was not amps that killed the MOSFETS. More likely, you killed the TVS diode. It's voltage spikes generated from the track, train, and wiring inductance and capacitance. Each time you open circuit an inductor after passing current- that creates a several hundred volt spike.
Both FETS are IRFZ34 https://www.vishay.com/docs/91290/91290.pdf
The TVS is a 1.5KE51CA https://www.digikey.com/en/pro...QDEsAVAWgDkAREAXQF8g
Thanks to @stan2004 for this previous post.
@stan2004 posted:This OGR thread might be related. If your symptoms are similar there are 2 transistors that behave like the iconic "triac" used to control the AC track voltage.
The IRFZ34 is (was) a widely used part and is readily available. Example from Amazon shown above. Given USPS package postage rates start at about $5, while you obviously don't need 10 pieces, I'm not sure you'll find a much better deal shipped to your door. Well, I did look on eBay and there are some U.S. sellers where you might save a buck or so...
