UDA50 Disk Controller

This document is the maintenance guide for the UDA50 Disk Controller. It covers the maintenance philosophy, field replaceable units (FRUs), and procedures for fault isolation. The guide details how to perform self-diagnostics upon power-up using resident diagnostics, how to interpret LED maintenance displays for error codes, and how to use host-resident diagnostics to isolate faults to either the UNIBUS or the disk drives. Additionally, it contains comprehensive tables for troubleshooting error codes found in the Status/Address (SA) register and interpreting real-time drive states and status message bytes.