Due to its critical role, WPC refurbishes 51109684-100 UCN power supplies by replacing electrolytic capacitors, installing a new fan and system testing to verify output voltage specifications for a minimum of 48 hours. The Honeywell 51109684-100 power supply is one of the silver power supplies often considered the heart of the xPM power system and as such all must pass our multi step test procedure prior to being certified for release.

Three voltages are present on the xPM power supplies. 24 VDC rated for 20 amps is available with either one or both supplies present. Secondly, the left supply (considered the primary) produces 6 VAC for use by LLAI lOPs to reduce AC noise interference. Finally, 3.9 volts is provided by the rechargeable batteries mounted on the power system panel to maintain the CMOS memory when 24 VDC is not present.

Recommendation is for a redundant power supply configuration having each power supply fed by its own dedicated power source. Even with redundant power supplies, care must be taken when changing out a failed power supply. This is to minimize disturbance of the environment and to reduce the introduction of particles into the area around and near the power supplies. Those particles can be pulled through the airflow of the working power supply and result in the second power supply failing.

In October of 1996 Honeywell issued a customer priority notification (PN #1986) about a possible over-voltage issue with the black colored (51109456-200) power supplies that were sold from 1988 through 1994. The Honeywell recommendation was to change out those black power supplies with the new silver version. Honeywell still recommends and strongly suggest that these black power supplies be replaced with the current power supply regardless of when they were put into service.

There have been three part number versions of the silver power supplies, their individual part numbers are as follows.
51109684-100
51198947-100
51198651-100