Hi, well NO it's not the motor and there are no diodes inside the motor, thats not actually the way they in which they are made to rotate and reverse direction.
This is done by "Driving" the motor with a pulse width modulated signal, that makes the motor spin,as the electricity is switched from pole to pole the motor's stator is attracted to that pole and moves forwards or backwards depending on the direction of the waveform.
So whenever a motor isn't working, spinning, then most often if the motor works, as it actually appears your is OK, then the "Controller' is at fault. The controller in this case is the Main Controller Board. This must be replaced in it's entirety. If you wish to DIY, then please find below a service and repair manual, to use to try and track down exactly whats wrong...
service and repair manual above..
But you see these days, it is nearly always my professional opinion that one should always get a "Quote" from the manufacturers recommended service center,Anma in your case, please contact a local or head office and ask for a referral to an Authorised service center. I cannot stress how important that last point is. It is even worth the cost of shipping. You see an authorised service agent, will have trained staff, trained on their brand, also they have first hand access to parts, original parts. This will actually save you money and ensure you can actually get it back fixed. Of course asking for a "Quote" also gives on the option of repair or replace. Often my clients,do not go through with repair, unless it is moderate, but in some of the more costly jobs they see it, as do i, that a replacement, with a warranty, is a better option.