Hi, We have been searching for information on this subject for quite awhile but it seems to be top secret or something. We have an HSD50 controller that comes up with a corrupt or incorrect serial number error which renders it inoperable. There is a way to re-enter the serial number and other base information. We have heard it referred to as Dangerous or Field Service Mode. It can't be too dangerous if the controller is already inoperable. A DEC Field Service Rep walked one of our Techs through how to reset the base information a number of years ago but the person and information are now long gone. We have not had much luck with these questions through HP/Compaq/DEC these days. Has any ever heard of this mode, how to get into it, and the commands needed? Thank you. Chris