Bosch WFF2001 will not spin

Hi everyone, reading entries in this forum, this seems to be a common type of problem but can someone help with a testing process to eliminate the various causes so I can order the correct replacement part to fix this?
Machine is a Bosch WFF 2001 about 5 years old.
approx 1 month ago the drum stopped rotating and after reading various forums I ordered replacement carbon brushes. Once fitted, these fixed the problem and the machine has been working brilliantly. At the same time, I replaced the drain pump which had become noisy and the machine has been working like it did when we first bought it.
However, yesterday the machine started spinning and then suddenly came to stop. It tripped the house main RCD. Subsequently everything works on the machine – wash, rinse and drain but the machine will not spin. It sits there with the pump running – a noticeable click from the main controller but the spinning ctcle will not work. Switching to a spin programme, we get the same result – no spin.
As the brushes are new, is this likely to be the controller or are there other possible causes? How do I test each component so it can be eliminated as a cause?
Many thanks