Due to its critical role, WPC refurbishes 51198947-100 UCN power supplies by replacing electrolytic capacitors, installing a new fan, and performing system tests to verify output voltage specifications for at least 48 hours. The Honeywell 51198947-100 power supply is one of the silver models, often regarded as the heart of the xPM power system. All units must pass a multi-step testing procedure before being certified for release.

The xPM power supplies provide three voltages:

• 24 VDC (rated for 20 amps), available when one or both supplies are operational.
• 6 VAC from the left (primary) supply, used by LLAI IOPs to reduce AC noise interference.
• 3.9 V from rechargeable batteries mounted on the power system panel, which maintains the CMOS memory when 24 VDC is unavailable.

For optimal reliability, it's recommended to configure redundant power supplies, each connected to its own dedicated power source. Even with redundant supplies in place, care should be taken when replacing a failed unit. This helps minimize disruption and prevents particles from contaminating the area around the power supplies.

In October 1996, Honeywell issued a customer priority notification (PN #1986) about a potential over-voltage issue with the black-colored 51109456-200 power supplies, sold from 1988 to 1994. They recommended replacing these black power supplies with the newer silver version. Honeywell still strongly advises replacing any remaining black power supplies, regardless of their service date.

There have been three versions of the silver power supplies:

• 51109684-100
• 51198947-100
• 51198651-100