M5902 Full Duplex TTY Transceiver

This document is an Engineering Change Order Log from Digital Equipment Corporation for the M5902 Full Duplex TTY Transceiver, used with PDP-11 Family processors.

It details two engineering changes:

1. M5902-00001 (January 1973): Addressed a production problem due to the unavailability of the 8837 hex inverter, which was used for hysteresis. The correction was to replace it with a 7404 inverter, which meant giving up the hysteresis feature. This change was effective for February production.

2. M5902-C0002 (September 1973): Resolved an issue where the #19-10845 optical coupler lacked a base connection, preventing the transistor from turning off correctly with LA30 units. The solution was to replace it with the #15-10727 optical coupler, specifically at locations E1, E2, E6-E9, E13, E14, and E21-E28. This rework was to be performed in-plant only when symptoms were present or where M598 was used, and mandated field rework for all M5902s in DJ11s serving as LA30-S interfaces. The estimated installation and test time was 1.5 hours, with kits including F1041-FCO/Prints and parts.