I troubleshot the unit using the diagram and information contained on the sheet of paper inside the unit. I found that all the AC voltages were good going to the power PCB. I checked the sensor and thermistor resistance ranges as listed on the paper but I didn't have all the DC voltages at the CN4 plug as listed. I tried to determine what component was bad on the board but I could check the IC and battery so I decided to try a new board. That corrected the problem.