What is the TTC103 component that has the volt transformer and how to know if it still works

I do not understand why you want to know that, but hey, it is a thermal resistor, a component that at different temperatures through it varies internal resistance, so it can be used as a thermal fuse or temperature sensor among other things. A TPA should measure approx 10K and as the temperature goes up, lower its R, it depends on where you use it the manufacturer is for your use. I hope you solve. Salu2