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The 5 V dc standby power is provided by both power supplies and connected together
on the I/O planar directly because the power supplies contain overload protection
against one supply shorting the other. Standby power of +5 V dc is provided to a
portion of the I/O planar, which is part of the system SPCN logic. This consists of
several components, including a logic chip, ROM, SRAM, and transceivers. The service
processor is not on standby power. Both power supplies provide +12 V dc to the fans in
the drawer to ensure sufficient cooling if one of the supplies fails. However, the
short-circuit prevention is on the I/O planar to protect against inadvertent shorts in one
line, causing the +12 V dc to fail completely.
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Chapter 1. Reference Information
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