I wouldn't know which are even diodes unless I know what the silkscreen print of the board is to look for. As for acting weird, I have a locomotive that will just stop moving after a while, but the sound keep going like it's in motion. But as soon as I push the direction button twice (Once to neutral, then to reverse.) it goes again like nothing happened. And it's random if and when it does it.
Like I said, the sounds keep going, so I know it's getting power just fine, and keep going. There is something on the board between the power in and the motors that is breaking the circuit.