I have a P3P with a GLB300A model. The USB circuit board is not working but I noticed that the GLB300A and GLB300B circuit board models are different. A repair shop tried a board off of a GLB300B controller and it did not work. (Maybe that board was bad who knows???) So I'm guessing they are not interchangeable right? Or should they be?
Also would  a GLB300B controller work with a P3P originally working with a GLB300A???

There are three types of P3A/P3P Controller: GL300A/B/C. The hardware are different but share the same function. You can try to link RC.