M7700

This document is an Engineering Change Order Log from Digital Equipment Corporation for the M7700 module, which functions as the Index, Photoamp, and Sector Counter for the RK05 disk drive, compatible with PDP-8, PDP-11, and PDP-15 processor families. It details various problems and their corresponding corrections identified between November 1971 and July 1973.

The key issues and their solutions outlined include:

1. System Stability & Reliability: Addressing false triggering in sector sensor amplifiers and one-shot circuits caused by power supply ripple and noise through component additions (capacitors) and signal rerouting (M7700-00001, M7700-00004). It also corrects a power-up race condition leading to false write protection in the RK05, particularly with RK11-D controllers, by modifying the BUS WRITE PROTECT gating logic (M7700-C0008). Issues with incorrect indicator lighting and marginal index separator operation due to component tolerances were also resolved (M7700-00003).
2. Functionality & Compatibility: Adjusting INDEX/SELECTOR timing (M7700-00005) to ensure cartridge interchangeability between RK05 and RK03. Crucially, it addresses the incompatibility between the RK05 (M7700 module) and the RK11-D controller by modifying the M7700 to accept both four-line linear and three-line BCD drive selection signals (M7700-C0006).
3. Documentation & Schematics: Multiple entries focus on correcting and adding missing or incorrect reference information, signal designations, and connection details within the circuit schematics to improve clarity and understanding (M7700-00002, M7700-00005, M7700-00007).

Each entry specifies the code, date, problem description, detailed correction (often involving component changes, etch modifications, or wiring instructions), and implementation details like "in-plant effectivity," "field effectivity," and prerequisites.