BA11-L Mounting Box Maintenance Manual

This document is the Preliminary Maintenance Manual for the BA11-L Mounting Box, manufactured by Digital Equipment Corporation.

The manual provides comprehensive information for the installation, operation, and servicing of the BA11-L, a rack-mounted expander box designed to house logic modules and supply power to components within a system, specifically for PDP-11/34 and PDP-11/39 Processing Systems.

Key aspects covered include:

• Physical Characteristics of the BA11-L: It is a 19-inch wide, 5 1/4-inch high, 25-inch deep unit, designed for high accessibility and serviceability, divided into sections for logic and power supply. It features a wraparound envelope for rack mounting.
• H777 Power Supply: A compact, modular power supply (up to 240 watts regulated DC output) that fits into the BA11-L. It consists of five subassemblies: AC control, +5V main regulator, MOS regulator, Core regulator, and Fan. The power supply incorporates various protection circuits, including inrush current limiting, overload/short circuit protection, overvoltage (crowbar) protection, power fail detectors, and battery monitor circuits.
• Optional H775 Battery Backup Unit: An external module designed to provide DC refresh power to MOS memory during power line outages, supporting 32K MOS memory for a minimum of 2 hours. It includes an automatic shut-off circuit and a charge status signal.
• System Units, Options, and Harness: Details the DEC System Unit concept, focusing on the DD11-P nine-slot backplane. It describes the SPC (Small Peripheral Controller) bus and the MUD (Modified Unibus Device) bus, which support memory modules and interfaces.
• Maintenance Procedures: The manual outlines both preventive and corrective maintenance. Preventive maintenance involves mechanical and electrical checks, such as inspecting wiring, fans, filters, and capacitors. Corrective maintenance focuses on fault isolation and replacement of defective regulators, providing flowcharts and detailed circuit descriptions for troubleshooting the H777 power supply and its various subassemblies.