Ok, I have a Down East Spa Bar Harbor. Paperwork says it is a 2000 model but manufacture date on the control pack and serial numbers point to 1999. Anyway, it had a Balboa MAS25 Rev 1A, v/n 51999, model X300960, control board with a 2 button control panel. I had a heater relay stick and scorch the board beyond repair. The 51999 is no longer available and was replaced with the 52000. The standard 52000 is no longer available and was replaced with the 52000 Lite Leader. After installing and chasing down revised wiring diagrams I got it installed. After install, the top side controls did not work, couldn't change speeds, lights, or temp setting. It only showed temp and that it was heating, with low pump running with the heater. I figured I would let it go and heat up as the temps were supposed to get below freezing and deal with the top side later. I went out in the AM and it was shut down displaying OH (overheating). I reset the breaker and it ran through the standard blinking 0 a few seconds, then flashed 99 and went to Sn. The owners manual just states Sn means either hi limit or water temp sensor malfunctioning. Balboa manuals says Sn means sensors are more than 2 degrees out of sync, or one or both are bad. I tested the sensors and they are within 2 degrees of each other, and that is with the hi limit sensor put in the tub right next to the water temp sensor after a few hours. I plan on ordering new sensors since they are fairly cheap and are almost 20 years old. Any ideas other than the top side may not be compatible with the new board (although I tried it with the old MAS25 rev 1A chip in it with the same results)? I am considering jumping the sensor plugs with a couple of 22K resistors to trick the board into thinking it is at 46 degrees and see if it will start up so I can trouble shoot the top side.