Led Board; Power Supply; Peripheral Components - GE Giraffe OmniBed Service Manual

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Chapter 1: Functional Description

The RS-485 integrated circuit converts the RS-232 TTL signals from the microcontroller to RS-485 signals for the

bus.

The timekeeping RAM has a battery integrated into the chip so that the time and date run are kept current

even with the power off. The battery has a minimum life of 10 years. Operator configuration values, patient

information (trending), and the error log are stored in this RAM.

The graphics controller is an S-MOS VGA controller. The graphics controller interfaces the data from the video

RAM to the EL display. The controller also synchronizes the display using a horizontal pulse (LP) and a vertical

pulse for the whole display frame (YD). The controller handshakes with the 80C188 using the READY line to

eliminate any lost data during display refreshes.

1.4 LED Board

The LED Board contains five display banks and two display drivers. One of the display drivers controls the

patient temperature and air temperature display banks. The other driver controls the patient set temperature,

air set temperature, warmer bar graph, and the mode and override indicators.

This allows the two large displays (patient and air temperature) to be multiplexed at a slower rate than the

other LEDs. This results in brighter large displays. Each driver has a brightness potentiometer that is preset at

the factory and should not be adjusted in the field.

The universal input switching power supply converts the line voltage to +5V DC and +12V DC. This supply can

source up to 75 watts. The 5 volts powers the electronics and the 12 volts is used by the EL display and for

future boards. Acceptable voltage ranges are 4.75V - 5.25V and 10.8V - 13.2V.

For the heater isolation transformer with relay board revision 9 or lower, the heater isolation transformer

isolates the incubator and radiant heaters from the mains voltage. The primaries mains input voltage comes

from the relay board and is switched by safety relay 1 and is also routed through the heater current sense

circuit. The dual primaries are connected in parallel for 115 volt operation and in series for 230 volt operation.

The isolated secondary output voltage is always 115 volts and goes directly to the solid state relays and the

incubator and radiant heaters.

For the heater isolation transformer with relay board revision 10 or higher, the heater isolation transformer

isolates the incubator and radiant heaters from the mains voltage. The primaries mains input voltage comes

from the relay board and is switched by safety relay 1. The dual primaries are connected in parallel for 115 volt

operation and in series for 230 volt operation. The isolated secondary output voltage is always 115 volts and

is input to the relay board where it is used by the heater current sense circuit. It then outputs from the relay

board to the solid state relays and the incubator and radiant heaters

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