TU77 FCOs

This document comprises a Field Change Order (FCO) and a series of Field Service Technical Manual (Tech Tip) updates for Digital Equipment Corporation's TU77 and TU78 magnetic tape drive systems.

The primary FCO (TU77A-M0007) details a mandatory upgrade to address significant reliability and performance issues, including tape damage (capstan wraps, stretching), loading difficulties, high noise levels, and premature module failures. This involves:

• Replacing Control Modules: Swapping older Control M/M2 modules with newer Control M2 modules (29-13774 at revision "G" or later).
• Retrofitting Components: Installing new rocker-style switches, bracket assemblies, and foam/front door modifications.
• Mechanical Adjustments: Modifying exhaust hose and air cooler mounting.
• Applicability: This FCO applies to specific TU77A serial number ranges (WS06000 through WS09350).

The subsequent Tech Tips provide a broad range of information for field service personnel, covering:

• Hardware Replacements and Upgrades: Procedures for replacing components like the cartridge opener motor, interconnect boards (D and F), AC blower/compressor drive motors, door latches, capstan wheels, and transducer assemblies. They also detail updates to control modules (M2) and associated parts.
• Adjustments and Calibrations: Instructions for read skew adjustment, NRZI threshold calibration, interconnect F1 board gain adjustments (R30 & R31), BOT/EOT (Beginning/End of Tape) sensor tuning, and cartridge pressure adjustments.
• Troubleshooting and Reliability Issues: Addressing common problems such as VAX/TU77 data correctable errors (often due to missing wiring), vacuum leaks around the buffer box door, intermittent failures caused by loose terminal screws or missing resistor packs on modules, power supply ripple from loose filter capacitor connections, and load failures stemming from dirty reflective tape.
• Manufacturing and Design Flaws: Identifying and providing solutions for issues like improper M8940 board seating and card cage vibration.
• Documentation and Part Number Clarifications: Correcting errors found in the TU77 Technical Manual, clarifying part numbers for various switches, relays, and other components, and providing wiring diagrams and decal placement instructions.

In essence, the document serves as a comprehensive resource for maintaining, troubleshooting, and upgrading the TU77/TU78 tape drives, detailing specific modifications, repairs, and procedural updates to ensure optimal performance and reliability.