There are a few things to check:
– Unplug the main power connector. Instead, use a USB cable connected to a USB power source to check if the controller can power on. If so, that means the microcontroller is still alive.
– Check your transformer to see if the transformer is still alive (if this is a 24VAC transformer, measure the AC voltage output; if this is a DC transformer, measure DC voltage). It could be that the transformer is burnt.
– Visually check the TVS diode right above the sensor port. That TVS diode is there for high voltage protection. It could be that the TVS diode is burnt. If there is no visual damage, use a multimeter to measure the resistance across the TVS diode.
The circuit actually has internal protection against accidentally plugged in COM wire to the sensor port, so I doubt is the microcontroller itself is damaged. It’s probably some peripheral element that’s burned.