AEG micromat combi 663 e?

The unit is completely dead.
The fuses are ok, I have opened up the oven and there is a 240v supply to the terminals.
I have tried to remove the pcb's but the selector/timer knob is holding them in via the front casing.
I have tried to pull the knob off without success.
How can I remove the selector/timer knob to enable the pcb's to be removed.