Novametrix Medical Systems OXYPLETH 520A, Service Manual

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2726 Power Supply Board
5-Jun-01 Model 520A Service Manual
17
PRELIMINARY
(VBAT-). The battery power will conduct through D3 and F301 to VIN at E302 pin
1 to the 2471 main board. The arrangement of R1, R2 and D2 bias Q1 off in this
condition which prevents power from reaching IC1, IC2 and IC3. The output of IC1
is also protected by D5 which is now reverse biased, the bridge D1 is also reverse
biased and prevents T301 from discharging the battery. With no voltage at IC2 the
LINEST will be low which indicates to the main board that there is no AC power.
2726 Power Supply Board
9.2
The 2726 Power Supply Board contains the circuitry needed to power the monitor
from the AC Mains (line voltage). The power supply board also connects to the
battery and contains the battery charging circuitry.
AC Mains and Battery Operation Overview
9.2.1
The Model 520A can be powered from its internal 12 volt battery or from the AC
Mains. The green (sine wave icon) front panel indicator illuminates when the line
cord is connected and the rear panel power switch is in the “|” (On) position. This
indicates that AC Mains power is reaching the power supply, that the battery is
being charged, and that if the monitor is turned on, it is being powered from the line
voltage.
If AC Mains power is removed by unplugging the line cord or setting the rear panel
power switch to the “0” (Off) position, the monitor will operate for up to four hours
from its internal 12 volt lead-acid battery. As the battery voltage runs low (<11.5
volts), the red battery indicator on the front panel illuminates. At this point, the AC
Mains should be reconnected to power the monitor and charge the battery.
If the monitor continues to be powered from a battery in a low voltage situation, at
approximately 11 volts, a continuous alarm sounds for thirty seconds while the
Message Center displays BATTERY EXHAUSTED CONNECT LINE CORD. If
this alarm/message is ignored, the monitor displays will shut down and the battery
indicator will flash on and off about every 5 seconds. If AC power is now restored,
the monitor will re-initialize (go through the power up and self-test routines) and
resume normal operation. However, continued battery operation will eventually
activate a hardware low voltage circuit (<8.5 volts) that shuts the monitor off to
prevent damage to the battery. Once the unit is shut down with the hardware circuit,
the AC Mains must be connected and the front panel POWER key pressed before
the monitor will turn back on.
AC Mains Operation
9.2.2
The AC Mains voltage enters the monitor at the rear panel Power Entry Module
(PEM). This device contains a built in RFI power line filter, a double-pole single-
throw switch that opens and closes both AC input lines, fuses, and an input voltage
selection card.