M7278

This document is an Engineering Change Order Log for the M7278 DH11 Register and Byte Control module, which is part of the PDP-11 Family of processors. It details three significant issues and their corresponding corrections from 1973:

1. Documentation Errors (April 1973 - M7278-00001): Field Service faced difficulties finding signal sources on prints, tedious wire list references, and an incorrect capacitor (C20) shown on diagrams that didn't exist. Corrections involved adding signal source references, deleting the erroneous C20, and fixing general drafting errors.

2. Hardware Manufacturing Defect (May 1973 - M7278-D0002 & September 1973 - M7278-D0003): A critical hardware problem was identified where an incorrect etch line position caused E74 pin 8 to short to E74 pin 7 (ground). This resulted in parity operation being permanently enabled, a condition often undetected by diagnostics.

   • Interim Correction: For existing "B" revision boards and those in stock, a physical rework was required, using an Xacto knife or similar blade to separate the incorrect etch path.
   • Permanent Correction: A new "C" revision board with a corrected etch layout was to be produced.
   • Effectivity: Boards shipped after June 4, 1973, were to be inspected. All M7278s in stock required immediate rework, and field units were to be reworked during scheduled maintenance or if symptoms appeared. Each rework was estimated to take 0.3 hours.