UDA50

This service manual provides comprehensive maintenance and troubleshooting procedures for the UDA50 Disk Controller, emphasizing a module replacement philosophy rather than component repair. It details the controller's Field Replaceable Units (FRUs) and outlines three main maintenance features: UDA50-resident diagnostics, LED maintenance displays, and host-resident diagnostics.

The document covers setting up UNIBUS address switches and jumpers, including UNIBUS tuning and priority plug configuration, and installing bootstrap ROMs. Fault isolation is a key focus, explaining how to interpret UDA50 LED error codes and Status/Address (SA) Register error codes to identify the most likely faulty FRU (M7485, M7486, or the host CPU).

Host-resident diagnostics, available for PDP-11 (CZUDC) and VAX (EVRLA) systems, consist of four tests: UNIBUS interrupt/address, disk-resident diagnostic, disk function, and disk exerciser. The manual provides guidance on interpreting their output, including SA register contents, data comparison errors, real-time drive state and status (RTDS) messages, and various subsystem error messages (host, UDA initialization, interrupt handler, and diagnostic machine errors). Detailed sections explain how to decode VMS, RSTS/E, and RSX error log reports, including common error log message definitions and packet formats. Finally, it introduces SPEAR (Standard Package for Error Analysis and Reporting) as an advanced tool for fault analysis, noting that UDA50 problems typically manifest as SA register codes, while drive-specific issues are indicated by real-time drive state and status codes, requiring consultation of drive maintenance guides.