The motor control electronics are now exposed. For other models, the control board may look different. But you can often recognize the defective capacitor(s). Replace them and any additional defective resistors (if any). The triac is under a lot of stress and brakes easily. Replace it if necessary. The components listed are all very cheap.

In this case the 150 nF block capacitor, the adjacent 470nF capacitor, the 100 nF capacitor, the 150 kOhm resistor and the triac BTA08-600CW were replaced.

If you don't have all the parts, you should definitely replace the two oil paper capacitors 100 nF and 150 nF. It is best to use MKP capacitors, X2 - class, at least 275 V. The space between the connections (pitch) should fit, bend the connections slightly if necessary. (e.g. if the pitch is 22 mm instead of 20 mm)

150 nF block capacitor (pitch 20 mm)

470 nF block capacitor (pitch 15 mm)

100 nF block capacitor (pitch 20 mm)

150 kOhm resistor

Triac type BTA08-600CW