My Thermomix TM31 have started jumping up and down in RPM. I set it to say 7 and it idles up in speed, then falls gradually, then jazzes up to 7 again, falling. Often when i run it to high rpm it makes noise, as it is slightly crushing/vibrating, but the motor spins freely and nice, without any noise when manually turned. Bearings seems fine. I figured the noise comes from the motor rpm jumping up and down?
I desoldered the potentiometer and cleaned it in isopropanol. It looks semi closed, but the isopropanol is so thin and volatile, I guess some of it made it onto the wiper. I also measured it from 0 at one end to 24.4k at the other (I thought it was supposed to be 22k?). I don’t know if leftover carbon residue inside will make the rpm jump, or if there is something else?