Arena Service Manual
Figure 5-23. On/Off State, Audio Alarm, and Power Fail
The power fail alarm circuitry includes a CMOS power state flip-
flop powered by a 1 Farad (F) capacitor. The flip-flop, which can
be toggled by either the front panel power button or the Pentium
system controller, provides the following functions:
• When power is not supplied to the Instrument (the +5 V
supply is off) and when the flip-flop is in the on state, then
power is supplied from the 1 F capacitor to the audio alarm
device. When power is supplied to the Instrument, the flip-
flop's output state is read by the Pentium, which provides
indication of the intended Instrument power state. Also,
when the flip-flop is in the on state, power is supplied to
the front panel power switch LED.
• The power fail alarm occurs either if the Instrument loses
power while it is running, or if the front panel power button
is pressed "on" when there is no power supplied to the
Instrument. The alarm can be silenced by toggling the flip-
flop off by pressing the front panel power button.
5-40 157-1278-912 Rev A
November 2003
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