RK11-C

This document is an Engineering Change Order (ECO) Log for the Digital Equipment Corporation's RK11-C Disk Control unit, part of the PDP-11 Family, detailing modifications and corrections issued between February 1972 and June 1973.

The log records various problems and their corresponding solutions, primarily falling into the following categories:

1. Documentation Accuracy and Completeness: Numerous entries address missing schematics, timing/flow diagrams, accessory lists, and updates to parts lists for cabinet components, power controls, and other hardware. Revisions to the head alignment procedure are also noted.
2. Hardware Design and Assembly: Corrections include specifications for proper cabinet mounting (e.g., on foam cushions), correct fan configurations (e.g., ensuring front/rear mounting, adding a second fan for 240VAC systems), and the addition of protective elements like a bezel cover panel.
3. Electrical Wiring and Power Control: Issues corrected involve specific wiring additions for proper power fail operation and the integration or substitution of power control units (e.g., 860/861 Power Controls).
4. Critical Functional Error Handling: A significant change (RK11C-C0014) addresses a complex soft error condition. If a soft error occurs during data transfer requiring a head movement, and a new command is issued before the head movement completes, it could lead to a fatal Drive Error (DRE). This required substantial logic and wiring modifications to prevent the DRE.

Each entry specifies "In-plant effectivity" (how changes are implemented in manufacturing) and, for critical issues, "Field effectivity," outlining requirements for retrofitting existing RK11-C units in the field, often dependent on the operating system (RSTS, DOS, RSX, MUMPS).

Overall, the document outlines essential updates to correct design flaws, improve documentation, and ensure the reliable functionality and correct assembly of the RK11-C Disk Control system.