Our grandsons RK FEF wasn't running so they brought it to me. It seemed like the battery might be dead at first because it would just sit there and play some sounds. Whenever I'd try to get her going, it would ring 2 clanks. I disconnected the power and it played the idle sounds for a good long period. I removed the boiler and a cap fell out? It was slightly swelled on top where the wires protrude out. There was a space on the smoke board clearly marked with a circle the size of the cap and a white line to indicate the "-". So I soldered the cap back on and the engine wouldn't run. I disconnected the smoke unit and it ran for whatever reason, luck?
I checked and I didn't have the 330uf 35v cap. So I soldered on a 220uf 35v cap to see if it would work.
The engine ran fine after that.
I'll post pictures later.