Bad solar sensor or bad main board?

My Goldline/AquaLogic*controller recently started reporting “solar sensor short”. I disconnected*the sensor from the board, and the system reported an “open” circuit as expected.

Using an ohmmeter I verified the solar sensor resistance was about the same as the water and air sensors, and varied depending on temperature. I then connected the water temp sensor to the solar sensor on the board and once again the system reported a solar sensor short.

i got a brand new sensor and connected it to the solar sensor input and again the system reported a short...

It sounds like sensors are fine and the board has a problem.. any ideas? I don’t want to buy a $500 replacement board just to fix the solar sensor but micro controller debugging is not in my skill set..