H720 Regulator Board

This document is an Engineering Change Order (ECO) log for the H720 Regulator Board used in the PDP-11 family of computers. It details five specific engineering modifications implemented between 1972 and 1973 to address technical issues, including:

• Voltage and Circuitry Stability: Adjustments were made to SCR components, diode sensitivity, and capacitance to resolve high-voltage output issues during crowbar activation and sensitivity problems in the DC LO circuitry.
• Component Performance: Transistor and resistor values were updated to correct breakdown voltage issues that caused regulator instability under certain line voltage and load conditions.
• Documentation and Maintenance: The log records various corrections to the parts lists and Bill of Materials, as well as instructions for in-plant and field implementation, including estimated install times and required kit contents for specific revisions.