Hotpoint Aquarius super silent WD640, will not spin.

My son has a Hotpoint Aquarius super silent WD640 and when spin is selected the motor/drum rotates at the normal speed and not at spin speed. There are no fault lights showing and the pump is clear and running correctly there being no water left in the machine. I have checked the motor connections, circuit board and wiring and can see no obvious faults. Has anyone got any ideas what else I could check or maybe what the resistance readings should be though the motor windings. There are 7 connections to the motor on the main plug these being,
1 red
2 red
3 purple
4 grey
5 white
6 grey
7 grey
6 and 7 are looped together all the other wires go to the motor windings.
Thanks for looking.

Has it got a variable spin knob on the consol panel is it set to 1200 / 1400 is the presure chamber clear which is attached to the rear filter.

The main control dial has fast or slow spin options but at the moment these have no effect on the drum speed, it turns under power but not at spin speeds. I'm a bit lost with the filter you mention, not sure where to look for it?

Remove rear White cover and you will see a black rubber cup with a jubilee clip round it. Remove and see if it's clear and the bottle on the side of it that's the presure chamber.