H-TU55 MaintMan Nov66

This document is an Instruction Manual for the Digital Equipment Corporation (DEC) Type TU55 DECtape Transport, a solid-state, bidirectional magnetic-tape handling device introduced in 1966.

Key Aspects:

1. Purpose & Compatibility: The TU55 is designed for high-speed loading, readout, and program updating in DEC digital computer systems, operating as a fixed-address magnetic-tape facility. Its solid-state switching circuits offer improved reliability and are compatible with, and can be used to upgrade or expand, systems employing the older relay-based Type 555 DECtape Transport.

2. Functional Description:

   • Tape Handling: It uses 0.75-inch magnetic tape with five channels (three for data, one for mark, one for timing), each made of redundantly paired tracks. Data is recorded using the Manchester phase recording technique, which makes precise tape speed less critical (speed varies ±20%).
   • Drive Mechanism: Tape motion is controlled by 600-rpm induction motors directly driving the reels, eliminating capstans, pinch rollers, or drag pads. Solid-state SCR (Silicon Controlled Rectifier) circuits control motor torque, and electromagnetic brakes ensure precise stopping.
   • Control Logic: The TU55 receives commands from an external DECtape control unit. It incorporates FLIP CHIP logic modules (including R202 Flip-Flops for motion and direction, and G850 SCR Motor Drivers) to manage tape movement and interpret commands. A W513 Level Amplifier ensures compatibility with different signal levels from older control systems.

3. Operation:

   • The transport can be operated in either remote (programmed) mode, via computer commands, or local (manual) mode using front panel rocker switches.
   • A thumbwheel selector allows the operator to assign a unit address (1-8) or set the drive "OFF LINE."
   • A "WRITE ENABLE/WRITE LOCK" switch controls write permissions.
   • Tape loading involves setting the unit to "OFF" to release the brakes, manually threading the tape, and then selecting the desired operating mode.

4. Physical & Electrical Characteristics:

   • It is a standard 19-inch rack-mountable chassis (10.5"H x 19.5"W x 9.75"D) designed to extend forward for maintenance.
   • Power requirements include +10VDC, -15VDC (typically from the DECtape control system), and 115VAC. An internal fan provides cooling.
   • The read/write head's azimuth is factory-set and cannot be adjusted in the field; if faulty, the head must be replaced by DEC.

5. Maintenance:

   • The manual provides detailed preventive maintenance schedules (weekly and monthly), emphasizing cleaning tape handling surfaces and running diagnostic routines. Head skew is noted as non-field adjustable.
   • Adjustments cover tape tension and transport stopping, involving trimpots for drag and stop torque, and a delay setting.
   • Troubleshooting guidelines are provided, focusing on checking logic circuit signal levels, verifying motor/brake truth tables, and identifying common fault sources (e.g., G850 modules, electromechanical issues).
   • A list of recommended spare parts is included.