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This document is an Engineering Change Order (ECO) Log for the Digital Equipment Corporation 725 TU56 Power Supply, spanning from February 1970 to November 1973.

The log details various problems identified with the power supply and their corresponding corrections. The changes primarily fall into the following categories:

1. Manufacturing and Physical Design Improvements: Addressing issues like improper chassis insulation, facilitating hardware replacement, improving component mounting (resistors, capacitors), optimizing wiring methods, and designing new harnesses to improve manufacturing efficiency and adaptability for different input voltages (110 VAC/220 VAC).
2. Labeling and Documentation Corrections: Ensuring consistency and accuracy of decals and silk-screened information (e.g., input voltage labels, connection instructions, fuse values) and correcting their placement.
3. Critical Electrical Performance and Safety Enhancements: This is a significant focus, with several entries dedicated to resolving:
   • Grounding Issues: Addressing ground loops that caused data errors and jerky motor operation in TU56 tape systems, and ensuring proper AC grounding to the chassis, which was sometimes inhibited by paint.
   • Safety Compliance: Re-rating the power supply to meet Underwriter's Laboratories (UL) standards.
   • Fusing Errors: Correcting improper fusing for 220 VAC configurations to prevent transformer damage and fire hazards.
   • Compatibility: Adjusting the power supply to accept both 125 VAC and 250 VAC plugs.

Each entry includes details on the problem, the specific correction, and the "effectivity" (when the change was implemented in production or required as a field retrofit, often with estimated installation times and parts).