The control and CPU electronics located on the left rear of the main frame.
In fact, this is the only real part of the kit that I'm really disappointed with. The PCB was engineered really for cost reduction by area. This means the connectors always get bunched and not placed into logical positions to allow for easy connections. This is then hampered because the 3 layers (of wafer thin) of plastic case don't really do anything.
If the PCB had been engineered against need layout (making it larger), then it would have been easy to connect things and easier to design a case that really supported and protected it.