Failure of TK50/TQK50 Subsystems

This document, Field Change Order (FCO) TQK50-R002, addresses issues with TK50/TQK50 magnetic tape subsystems in 16-bit PDP-11 Q-Bus systems. The documented problems include failures during backup/verify, difficulties recovering from user-aborts, and NXM (Non-Existent Memory) errors during write operations.

Key steps for technicians: * Applicability: Strictly for 16-bit Q-Bus systems. Do not install on 32-bit systems. * Hardware Upgrade: Technicians must replace the FPLS ROM and High/Low Byte ROMs on the M7546 module. * Configuration: Following the hardware update, the module revision must be updated using provided labels, and switch pack E38 must be reconfigured to reflect the new hardware/module revision level. * Software: For systems running DSM11 version 3.3, a specific software patch (4.2.98) is required. * Verification: Technicians should observe M7546 LEDs during power-up to confirm successful microdiagnostic completion.