Wired doorbell T8200 shorted out?

Hi, my doorbell stopped working, so I tested the transformer (which was the correct one, purchased at the time of purchasing the doorbell.) had no output voltage. I bought a new, correct transformer and installed. I did notice a small spark as I hooked up the last low voltage wire, but didn’t think much of at the time. I then went out side to see if the doorbell was lit up, it was not. Again I checked out put voltage at the transformer and had nothing. I unhooked everything and tested all of the wiring for shorts and it all checked out good. I am thinking the doorbell unit itself is shorted internally which smoked both transformers. Has anyone else had this problem? By the way, the doorbell has been working great until about a month ago.