There are filter caps in the bottom of the machine that should be replaced, should be a orange one possibly 2 orange ones. I replaced them on my BH and never had a problem again with it reseting again. This usually happens when a high power coil fires on the playfield like a pop bumper or a sling target. Also do you have the original mpu and does it have any corrosion around the data sentry battery? If there is jthats where the reset section is and that will cause the game to reset at times.

The only way to fix this is to send the board out to be repaired. As an owner of a ni-waumpf board i strongly recommend getting your original cpu rebuilt. Theres alot of down falls to the ni-waumpf, its great to get a dead machine back up and running but it does not play the same as the original among many other problems.