Hotpoint WD420 error code (again!)

Number 4 light is flashing and from what I’ve managed to search on here, means the speed control on the main PCB has a problem.
Is this correct or can there be other causes of this error code?

It does make sense however, as the machine will work fine (drum turning) until it’s called upon to do a fast spin, then it stops and shows the error code.
I’ve checked the motor brushes and connections, which seem fine.
Could it be the speed sensor thingy on the end of the motor, or is it most likely to be the PCB? (I’ve already replaced this once a couple of years ago).
Thank you in advance for any help or suggestions.

Paul