An appliance's front button controls its operation. It does not necessarily disconnect the internal wiring from the 230 V mains supply, which can kill. A blank display can mean a faulty display, an interlock or an interrupted neutral; it cannot tell you whether a conductor is safe to touch.

This course's practical tasks are external checks and maintenance the manufacturer explicitly assigns to the user. Electrical covers, internal wiring and hardwired connections require appropriate competence, equipment and a safe working method. Reading a lesson does not provide those.

Before any user maintenance, find the exact model's instructions and follow its shutdown, disconnection, cooling and draining requirements. If that cannot be done safely, stop.