The PS-855B (and its predecessor, the PS-850) is an Emergency Power Supply (EPS) system commonly used in aviation to provide backup power for critical flight instruments. Proper maintenance is vital for ensuring these units function during a power failure.

Charging Times: Units with >50% capacity require 8 hours; <50% requires 16 hours.

Consumables: The manual lists required adhesives, tapes, and protective coatings for internal repairs. Core Specifications for Maintenance PS-855B Specification Input Power 28 VDC, 15 Amps Output Voltage 24 to 28 VDC (Emergency) & 5 VDC (Converter) Battery Capacity 5.0 Amp/Hour (higher than the 2.5 Ah on A/C models) Weight 13.7 lbs max Service Life Unrestricted, provided periodic checks are passed

The maintenance manual for this unit is not a simple user guide. It is a technical service document exceeding 50-100 pages, containing:

Scenario: +5V Rail Low (4.2V instead of 5V)

Step 1 – Visual Inspection (Manual Page 12)

  1. Personal Protective Equipment (PPE): Requirements for PPE, such as hard hats, safety glasses, and gloves.
  2. Lockout/Tagout (LOTO): Procedures for ensuring equipment is safely de-energized and locked out during maintenance.
  3. Electrical Safety: Precautions for working with electrical systems and components.

Warning: Avoid “free PDF” sites that require credit card registration. Authentic maintenance manuals are usually free or sold by authorized distributors for $15–$50.