Honeywell will discontinue all repairs on RM-850s by the end of 2013. The replacement, the RM-855 RMU is a liquid crystal display (LCD) unit, offering increased reliability and upgrade capability. Future functionality could include automatic dependent surveillance-broadcasting out (ADS-B Out).
Honeywell stopped production on RM-850s in 2006 and has not repaired failed cathode ray tube (CRT) RMUs since 2010. As of 2014, any failed RM-850 will require replacement.
The RM-855 does require a different mating connector on the airplane, and wiring details can be found in the Honeywell Primus II Integrated Radio System operation and installation manual (publication D198710000004), found online.
To access Technical Publications to request this manual click here.