88
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The current is equally shared (within +10%) by the two power supplies at maximum load. If one
power supply fails, the remaining power supply takes over. +3.3 V, +5.1 V, +12 V, -5 V, and -
12V power outputs have series-connected blocking diodes to prevent an output fault in one power
supply from pulling down the outputs of the other power supply.
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If one of the power supplies fails, an LED in that power supply either goes out or changes from
green to amber, and the power on LED on the front of the base unit changes from green to amber.
Look at the back of the base unit to see which power supply failed.
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If a power supply is not supplying all of its DC voltage output levels correctly, an audible alarm
sounds.
The pinout for the power supply connectors (which plug into J4, J5, J6 on the power distribution board)
is as follows.
Pin
Name Pin Name Pin Signal
1 AC Line 14 Ground 26 Ground
2 AC Ground 15 +3.3 V 27 Remote ON/OFF
3 AC Neutral 16 Current share +3.3 V 28 Ground
4 No connect 17 Current share +5.1 V 29 +12 V
5 No connect 18 Current share +12 V 30 +12 V
6 No connect 19 Current share return 31 +12 V
7 +3.3 V 20 AC OK
1
32 +12 V
8 Ground 21 DC OK
2
33 -12 V
9 +3.3 V 22 Ground 34 Ground
10 +3.3 V 23 -5 V 35 Ground
11 Ground 24 Ground 36 +5.1 V
12 Fan 1 Tach 25 +5.0 V - always on 37 +5.1 V
13 Fan 2 Tach
Pinout Notes:
1. The AC OK signal is a TTL-compatible signal. It monotonically (without wavering) transitions to
a high level to indicate that the AC input power is within 90 - 132 VAC or 180 - 264 VAC. The
signal provides the 3 mA sink/source current as well as any current required for the LEDs.
Provided that there is an AC input, this signal must be available to report whether or not the
outputs are functional. Overshoot should be kept to less than 1 V above a maximum steady-state
high-level output of 5 V. Undershoot should be kept to less than -1 V below a minimum steady-
state low-level output of 0 V.
2. The DC OK signal is a TTL-compatible signal, and its purpose is to initiate an orderly start-up
procedure under normal operating conditions. During power up, this signal should remain low
(less than 0.8 V) for at least 100 ms after all of the +5.1 V, +3.3 V, and +12 V outputs have
reached their minimum sense levels of 4.75 V, 3.14 V and 11.4 V, respectively. The signal then
monotonically (without wavering) transitions to a high level (greater than 2.4 V) to indicate that
the power source is stable. The signal provides the 3 mA sink/source current as well as any current
required for the LEDs. Overshoot should be kept to less than 1 V above a maximum steady-state
high-level output of 5 V. Undershoot should be kept to less than -1 V below a minimum steady-
state low-level output of 0 V.
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