Smiths Medical 1818R, Operation And Service Manual

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Chapter 9: Service Maintenance and Repair
9-6 Oximeter Operation and Service Manual
Test Equipment and Tools Required
To diagnose and repair the full extent of possible malfunctions on the
oximeter and display board, you will need the following test equipment
and tools:
• DMM volts/ohms/amps, with M
Ω
input impedance or greater.
• Oscilloscope, 50 MHz, with 10 M
Ω
input impedance or greater.
• Variable output DC power supply, 0-5 VDC at 200 mA or greater.
• Small Phillips screwdriver
• Small flat blade screwdriver
• Needle nose pliers
• Diagonal cutters
• Clip leads
• Low-power microscope or magnifying glass
• Soldering iron and solder
• Solder wick or solder remover
Connecting a DC Power Supply
To verify some of the voltage measurements that follow, you’ll need to
connect a variable output DC power supply in place of the three “C” cell
batteries. You must be careful to observe the polarity of J9 when doing this.
Follow these steps to connect a DC power supply in place of the “C” cell
batteries:
TXA0 Asynchronous serial communication transmit signal to RS-232.
VAMB VAMB is the output of the front-nd differential amplifier.
V-BT Battery voltage
VR Output voltage from the digitally controlled potentiometer.
VREF 2.5VDC reference to voltage.
V-RAM Voltage used to maintain trend information in RAM.
VCC,
VDD 5VDC used for digital output supply voltage.
/WDT Watch dog timer strobe