The PS-855B is an emergency power supply unit commonly used in aircraft to provide backup power for essential flight instruments, such as gyro horizons. Maintenance for this unit is typically governed by the L3Harris (formerly J.E.T. or B.F. Goodrich) Component Maintenance Manual (CMM) TP-483.
DATE: October 26, 2023 TO: Maintenance Department / Technical Management FROM: Technical Writing Division SUBJECT: Review and Summary of PS-855B Maintenance Procedures
A neglected PS-855B might show a "green" light during a quick preflight but fail five minutes into a real emergency. Regular adherence to the service literature ensures that when the master switch fails, your emergency instruments don't. ps-855b maintenance manual
PS-855B Maintenance Manual
Needed to test:
This report provides a structural and procedural overview of the PS-855B Maintenance Manual. The PS-855B (identified herein as the "Unit") is a high-performance Hydraulic Power Unit (HPU) used primarily in industrial mobile and stationary hydraulic applications. The manual serves as the definitive guide for installation, routine servicing, troubleshooting, and overhaul.
If the Test LED stays illuminated for the full 5 seconds, capacity is above 50%. The PS-855B is an emergency power supply unit
| Original Part | Type | Modern Substitute | Notes | | :--- | :--- | :--- | :--- | | 2SC5200 (NPN pass) | Power transistor | MJL4281A | Higher SOA, identical pinout | | 1N4148 | Signal diode | 1N4148 (still made) | No change | | 4700µF/50V (85°C) | Electrolytic cap | 5600µF/63V (105°C) | Improved ripple rating | | LM723 | Voltage regulator | UA723 or direct drop-in | Still in production | | 5k pot (voltage adjust) | Carbon potentiometer | Bourns 91A1A-B28-B15L | Sealed, longer life |
Troubleshooting and Repair