Dale, I'm fairly new to legacy, but old to troubleshooting electronics in general. As you are probably aware, it could very well be a bad circuit board component, but before that assumption is made, I would suggest "exercising" the connectors inside the loco. By this I mean, unplugging and reconnecting them, one at at time. Oxidation between compression connections can build-up over time. Sometimes just disconnecting and reconnecting will get things working again. Same for wire nuts. And of course it's always a good idea to take good pictures of the connections from different angles before starting, in case there's a question later about where something goes.