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This document is an Engineering Change Order Log from Digital Equipment Corporation for the H720 Regulator Board, used in the PDP-11 Family of processors.

It details several engineering changes and corrections issued between June 1972 and September 1973 to address various issues with the board. Key problems and their solutions include:

• June 1972: Correcting an excessive +5V output voltage during crowbar activation by changing an SCR and a resistor, and adding a new mounting bracket.

• November 1972: Resolving two problems:

  1. DC LO circuitry being overly sensitive to voltage changes by replacing a diode.
  2. +5V driver circuitry oscillation under high current loads by adding a capacitor.
  • This entry notes that no board relayout will occur, only rework, and that the changes may apply to some existing H720 Power Supplies in the field.

• April 1973: Approving an allowable substitution for certain capacitors.

• August 1973: Addressing an unstable regulator and crowbar issue caused by a transistor with too low a breakdown voltage by replacing multiple transistors and a resistor. This change was slated for production phase-in and field rework.
• September 1973: Correcting several documentation errors found in the Parts List, involving changes to item numbers, values, and tolerances.

The log specifies the problem, the exact correction (often component changes), and the "effectivity" or implementation details, including whether it's an in-plant rework, field rework, or documentation update.