A Thermador speed oven combines microwave and convection heating in one unit with a more complex control board than a standard built-in microwave, which means it has an additional set of parts that can fail — the convection heating element and fan, on top of the magnetron and control electronics a standard microwave also has.
Knowing which type you have — speed oven or standard microwave — helps narrow down what’s likely wrong before a technician even arrives, since the two platforms don’t share the same common failure points.