I've disassembled a simply PC-PSU fan motor.It contains two coils in two NPN transistors collector, the "second" transistor base coming from the "first" collector, and the "first" base coming from a bipolar HALL-element.The rotor is a sector-magnet.(N...S...N...S)
Maybe help for You....
p.s.: heres a ultraquick explanation of the principle:
a permanent magnet is mounted on the rotating axis, which is embeddeed into the errecting coils 'tube' - a electronic produces the pseudo rotating field by switching the coiles
Searching to increase the speed of an CPU cooler Fan, and don'n KNOW how it works.
It has 4 coils on stator and magnetical band on rotor.
How to rebuild the PCB to have variable speed ?