I have an MC-2100 REV B V#37376 board that is acting very strange. I had been experiencing the tripped breaker issue (started slowly tripping once and a while but now trips when starting at any speed). I tested the motor and it ohms out OK with no shorts and it runs when connected to a battery (19V). I sent the board in for repair/rebuild and anxiously waited for the return but alas when I got it back it acted the same way! While I was waiting for the board to come back I read through this forum and others trying to learn how to diagnose this board. When I got the board back and I placed it in the treadmill I tried it out with no load on the motor (disconnected the belt). I also switched plugs for the treadmill to another room and circuit. I started the treadmill on speed 1 and the motor started to race away and the treadmill breaker popped. Usually its the house breaker but this time the treadmill breaker. My board always shows a steady red LED with no flashes. I also tried the speed test with the motor disconnected and a light in its place. This time when I press any speed the light comes on momentarily (about 1 sec) then goes away. The LED is still steady no flashes and the control panel displays like normal. If I manually rotate the tread the speed registers. Like I said I did have the board rebuilt and it looks like there are new components on the board. I am not experienced in electronics but I do know how to use a multimeter. Any thoughts are greatly appreciated!