Here, on the first picture, you can see that the BROWN wire is NOT connected to the elctronics board. It is broken. So that is why the speaker does not work. It was bad soldered, so the wire came off.

On pictures two and three you see the parts of the wheel, the black rolls and the metal axles and how to put them on the yellow part.

The red part is the on/off switch button. Look how it fits right, look at picture one in Step one for a few of the position of that red button.