Smiths Medical 1818R, Руководство по эксплуатации и обслуживанию

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Chapter 9: Service Maintenance and Repair
Oximeter Operation and Service Manual 9-1
Chapter 9: Service Maintenance and Repair
The service maintenance and repair section contains circuit descriptions,
voltage test points, and waveform test points. The Appendix contains
detailed parts lists and circuit diagrams. It is intended for persons trained in
service, maintenance, and repair of modern medical equipment. Thorough
knowledge of this equipment’s operation is required before attempting to
repair this equipment.
General Description
The oximeter contains one circuit board. This board contains all power
supply, microprocessor, date acquisition, and display circuitry.
Power Supply and ON/OFF Circuitry
The power supply is built around a switch mode regulator IC U10. It is
configured as a fly-back regulator to convert input voltage in the range of
2.7-4.5 VDC into +5VDC output voltage. Negative voltage used by the
analog section is generated as a “by-product” of the main +5VDC supply.
Charge pump C55-D4-C69 is used to convert pulsatile voltage on the out-
put LX of U10 into negative voltage in the range of –4VDC to –6VDC.
The V-RAM voltage used by the on-off circuitry and RAM is generated
either from the battery, or from VCC when unit is on. V-RAM is taken
straight from the battery due to the maximum voltage being 4.5V. V-RAM
may ap3VDC as the battery power gets depleted, however, this
voltage is high enough to retain trend data in RAM. Capacitor C70 is used
to maintain V-RAM when batteries are being replaced. It can keep infor-
mation in RAM for more than 1.5 minutes.
On/Off circuitry is built around U7A-U7B flip-flop, which directly con-
trols regulator IC U10.
Digital Section
Microprocessor U11 is Hitachi HD64180. Its address and data buses are
connected to the One Time Programmable Read Only Memory (OTP
ROM) U12 and Random Access Memory (RAM) U24. Memory Address
Decoder is implemented using U17A demultiplexer chip.