The 51198651-100 power supply is the latest version of the silver power supplies for the xPM power system. This updated model includes design improvements to address potential failure modes. To maintain performance, WPC refurbishes UCN power supplies by replacing electrolytic capacitors, installing new fans, and verifying the output voltage specifications.

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.

The xPM power supplies provide three different voltages:

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

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, which were sold between 1988 and 1994. Honeywell recommended replacing these black power supplies with the newer silver version. They continue to strongly advise replacing any remaining black power supplies with the current model, regardless of when they were put into service.

There have been three versions of the silver power supplies:

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