Beko WMB61631S Motor issue

Hi,

my daughter has a Beko WMB61631s which recently stopped spinning. I figured it was probably the brushes so removed the motor to check, the brushes were fine but there was quite a lot of carbon all over the motor and especially around the brushes and commutator, I cleaned this up, but it still didn’t spin, I then found the motor control pcb had blown, 2 tracks were burnt out on the back and I tested the rectifier and this was bad, I figured that maybe the carbon build up had caused this, I tested the motor with my test meter and there was no short circuit or anything, I purchased a used motor control pcb from eBay and fitted it, now the motor does spin, but literally at full speed for a second or so then stops, then after a couple of minutes it spins again, but only for a second or so again. If I disconnect the motor tachometer from the main board it spins at full speed again but for longer, so I guess the main board is getting feedback from the tacho, I am asking if anyone knows if it’s possible the used board I bought is at fault, or, is it the tacho on the motor, or could it be the main board? Is there any tests I could do, I tested the resistance on the tacho and at rest it was about 90 ohms and this increased when the motor was turned.

any help would be much appreciated, I know she can’t afford a new machine right now but I don’t want to keep guessing and spend as much as a new machine on parts!