Hi.
There is only a probe sensor, located inside the oven cavity. This sensor controls both oven baking and broiling functions. If the problem is only when baking, then it is not the temperature probe.
The problem is usually the baking element. The element can be tested removing it from the cavity and reading impedance on the element's contact with the aid of a multimeter.
Multimeter must be set to read Ohms (impedance) on Rx1. If impedance is infinite (circuit open), then the element must be replaced.
In case the element is good, then the problem will be either the Electronic Control (what you called mother board, often called ERC), or a broken wiring.
Parts and diagrams available on Sears or Partselect website.
Here element from Partselect:
BAKE ELEMENT
Here all parts and diagrams: http://www.partselect.com/MultiModels.aspx?ModelNum=jtp18&searchTerm=&RefineSearch=0