One thing to note when replacing the main board...on most models, one of the installation steps requires that you remove or cut the #2 wire in the 9- pin harness which was used to moniitor a thermister. The new board does not utilize this circuit, so it was eliminated. Failure to remove the wire will result in erratic operation.
The instruction sheet that comes with the new board mentions which serial numbers must be modified like this to make the board function properly, so pay attention to the instructions.