The diagram reveals an auxiliary winding on the transformer that powers the PWM controller after startup. A startup resistor (typically 150kΩ – 470kΩ, 2W) from the bulk capacitor initially charges the VCC capacitor. If this resistor fails open, the board will "click" repeatedly as the IC tries to start and fails.
A combination of a high-power capacitor and the induction coil itself. The board alternates the switching of the IGBT (Insulated-Gate Bipolar Transistor) at frequencies between 20–30 kHz to create the magnetic field necessary for heating. User Interface (UI) Hookup: chk-v9.04g circuit diagram