Yes. You can do two things. Replace the swith curcuit board or replace the triac/tyristor on the board itself. The last solution requires you to unsolder the triac and loosen it from the heatsink(110v veriosn only. 230v version has no heatsink) and test it with a multimeter to establish if it has failed. (Testing of tracs can be googled.) In eather case you will need to open the casing.
1. remove the base palte by lifting the end opposite to the electric cord.
2. Loosen the bottom power outled slider, without removing it fully
3. unclip the curved plastic retainer in the front and unscrew philips head screw.
4. Work around the edges of the two halves until it comes apart and you are able to free the slider from its return spring.
Replace the cicuit board completely if available. Or resolder a new triac observing the orietation of the pins and reattach to the heatsink by riveting/cliping on or whatever applies to you model. Using heat conductive silicon paste between triac and heatsink is a good idea if it is originally fitted (if white paste residues can be seen). The European 230 v version do not have a heat sink, due to the higher voltage and thus lower current opassing through. If the Euro version, simply replace the triac, trim the pins on the back of the board nad put back in place.
Triacs can be obtained from any electronic componets dealer, as long as you can supply the code stamped on it. The Euro version has code TIC226N, which you can find in any component or manufacturer cross refereanse table. TIC226N basically means a 8 amp triac. Triac is simplified just a sort of ac transistor. The US version I do not have the code for, but it must have a higher ampere rating, thus the heatsink
Put all internal componets back in place in the right halve. Put the left halve on top and fit properly by gently pressing together. Fit the screw in the front and the retaining clip. Fit the sliding cover by cliping it back on, observing that the notch for the return spring will meet the spring pin on the right side for it to snap in place. The spring pin can be observed through the slots for the sliding cover. Then insert the base plate reversely of how you removed it.
The problems of these mixers, is that if overloaded the maximum current rating of the triac's may be exceeded. This will cause the triacs to short curcuit and therefore will give full power in any mode.
To avoid the problem, avoide heavy batters, heavy doughs and prolonged high load tasks. Otherwise a very handy smart little mixer that should last for years.