Mallinckrodt Nellcor N-20 User manual

Caution: Federal law (U.S.A.) restricts this device to sale by or on the order of a physician.
To contact Mallinckrodt’s representative: In the United States, call 1.800.635.5267 or 314.654.2000; outside the United States, call
your local Mallinckrodt representative.
0123
2000 Mallinckrodt Inc. All rights reserved. 062397B-0600
Service Manual
N-20/N-20P Portable Pulse Oximeter

Mallinckrodt Inc.
675 McDonnell Boulevard
P.O. Box 5840
St. Louis, MO 63134 USA
Tel [phone]
Toll Free 1.800.635.5267
Mallinckrodt Europe BV
Hambakenwetering 1
5231 DD's-Hertogenbosch
The Netherlands
Tel [phone]
Nellcor Puritan Bennett Inc.
4280 Hacienda Drive
Pleasanton, CA 94588 USA
Nellcor Puritan Bennett Inc. is a wholly owned subsidiary of Mallinckrodt Inc. Nellcor, Nellcor Puritan Bennett, Durasensor,
Oxisensor II, Oxinet, Dura-Y, Oxiband, and Oxicliq are trademarks of Mallinckrodt, Inc.
To obtain information about a warranty, if any, for this product, contact Mallinckrodt's Technical Services Department, or
your local Mallinckrodt representative.
Purchase of this instrument confers no expressed or implied license under any Mallinckrodt patent to use the instrument with
any sensor that is not manufactured or licensed by Mallinckrodt.
Covered by one or more of the following U.S. Patents and foreign equivalents: 4,621,643; 4,700,708; and 4,770,179.

iii
CONTENTS
1 Introduction.................................................................................................................................................... 1-1
1.1 Manual Overview ........................................................................................................................................ 1-1
1.2 Warnings and Cautions............................................................................................................................... 1-1
1.3 Description of N-20 Portable Pulse Oximeter ............................................................................................ 1-1
2 Routine Maintenance ..................................................................................................................................... 2-1
2.1 Overview...................................................................................................................................................... 2-1
2.2 Cleaning ...................................................................................................................................................... 2-1
2.3 Periodic Safety and Functional Checks ...................................................................................................... 2-1
2.4 Battery ......................................................................................................................................................... 2-1
3 Performance Verification .............................................................................................................................. 3-1
3.1 Introduction................................................................................................................................................. 3-1
3.2 Required Materials...................................................................................................................................... 3-1
3.3 Performance Tests....................................................................................................................................... 3-1
4 Troubleshooting ............................................................................................................................................. 4-1
4.1 How to Use this Section............................................................................................................................... 4-1
4.2 Who Should Perform Repairs...................................................................................................................... 4-1
4.3 Replacement Level Supported ..................................................................................................................... 4-1
4.4 Obtaining Replacement Parts ..................................................................................................................... 4-1
4.5 Troubleshooting Guide................................................................................................................................ 4-1
4.6 Service Procedures...................................................................................................................................... 4-5
4.7 Error Codes................................................................................................................................................. 4-7
5 Disassembly Guide ......................................................................................................................................... 5-1
5.1 Introduction................................................................................................................................................. 5-1
5.2 Required Equipment/Tools.......................................................................................................................... 5-1
6 Spare Parts ..................................................................................................................................................... 6-1
6.1 N-20/N-20P Spare Parts ............................................................................................................................. 6-1
7 Packing for Shipment..................................................................................................................................... 7-1
7.1 General Instructions.................................................................................................................................... 7-1
7.2 Repacking in Original Carton..................................................................................................................... 7-1

CONTENTS
iv
8 Specifications .................................................................................................................................................. 8-1
8.1 Readout ....................................................................................................................................................... 8-1
8.2 Controls....................................................................................................................................................... 8-1
8.3 Operating Modes......................................................................................................................................... 8-1
8.4 Printer Output ............................................................................................................................................. 8-2
8.5 N-20/N-20P Performance............................................................................................................................ 8-2
8.6 Sensor Types................................................................................................................................................ 8-3
8.7 Electrical Specifications.............................................................................................................................. 8-3
8.8 Environmental Specifications...................................................................................................................... 8-4
8.9 Physical Specifications................................................................................................................................ 8-4
9 Technical Supplement.................................................................................................................................... 9-1
9.1 Overview...................................................................................................................................................... 9-1
9.2 Functional versus Fractional Saturation .................................................................................................... 9-1
9.3 Measured versus Calculated Saturation ..................................................................................................... 9-1
9.4 Circuit Analysis ........................................................................................................................................... 9-2
9.5 Functional Overview ................................................................................................................................... 9-2
9.6 SpO2Analog Circuitry Block Diagram (Figure 9-3).................................................................................. 9-3
9.7 Definition of Terms...................................................................................................................................... 9-5
9.8 Overall Block Diagram ............................................................................................................................... 9-6
9.9 SpO2Analog Circuitry................................................................................................................................ 9-7
9.10 Digital Circuitry ................................................................................................................................... 9-12
9.11 Support Illustrations............................................................................................................................. 9-30
FIGURES
Page Number
Figure 5-1: Sensor Lock, and Printer, Paper, and Battery Access Doors...........................................................5-2
Figure 5-2: N-20 Covers with the PCB and Display Assembly............................................................................ 5-3
Figure 5-3: Main, Auxiliary, and Display PCB Assembly.................................................................................... 5-4
Figure 5-4: Printer and Flex Circuit Installation.................................................................................................. 5-5
Figure 9-1: Oxyhemoglobin Dissociation Curve .................................................................................................. 9-2
Figure 9-2: Overall Block Diagram........................................................................................................................ 9-3
Figure 9-3: SpO2 Analog Circuitry Block Diagram............................................................................................. 9-3
Figure 9-4: Digital Circuitry Block Diagram ........................................................................................................ 9-4
Figure 9-5: Power Supply Block Diagram............................................................................................................ 9-4
Figure 9-6: Display Control Block Diagram ........................................................................................................ 9-5
Figure 9-7: Printer Control Block Diagram......................................................................................................... 9-5
Figure 9-11: Variable Gain Circuit.................................................................................................................... 9-10
Figure 9-12: Filtering Circuit .............................................................................................................................. 9-11
Figure 9-4: Digital Circuitry Block Diagram ...................................................................................................... 9-12
Figure 9-14: N-20 Hardware Block Diagram..................................................................................................... 9-14

CONTENTS
v
Figure 9-15: Address Demultiplexing Circuit .................................................................................................... 9-15
Figure 9-16: Address Decoding Circuit .............................................................................................................. 9-16
Figure 9-17: CPU Memory Circuit ..................................................................................................................... 9-17
Figure 9-18: Input Port Circuit ........................................................................................................................... 9-18
Figure 9-20: Real-Time Clock Circuit ................................................................................................................ 9-19
Figure 9-21: Audio Output Circuit ..................................................................................................................... 9-20
Figure 9-6: Display Control Block Diagram ...................................................................................................... 9-20
Figure 9-23: User Controls Circuit ..................................................................................................................... 9-22
Figure 9-26: Analog Reference Voltage Circuit................................................................................................. 9-25
Figure 9-27: Ambient Light Circuit .................................................................................................................... 9-25
Figure 9-28: Ambient Temperature Circuit ....................................................................................................... 9-26
Figure 9-29: Battery Voltage Circuit .................................................................................................................. 9-26
Figure 9-30: Battery Type Circuit....................................................................................................................... 9-26
Figure 9-32: Printer Flex Circuit ........................................................................................................................ 9-28
Figure 9-8: LED Drive Circuit ........................................................................................................................... 9-30
Figure 9-9: Differential Synchronous Demodulation Circuit .......................................................................... 9-30
Figure 9-10 N-20 HSO Timing Diagram............................................................................................................ 9-30
Figure 9-13: AC Variable Gain Control Circuits .............................................................................................. 9-30
Figure 9-19: Output Port Circuit ........................................................................................................................ 9-30
Figure 9-22: Display Control Circuit.................................................................................................................. 9-30
Figure 9-24: Power Supply Circuit ..................................................................................................................... 9-30
Figure 9-25: Power Control Circuit.................................................................................................................... 9-30
Figure 9-31: Printer Interface Circuit ................................................................................................................ 9-30
Figure 9-33: N-20 SpO2Analog Block Diagram................................................................................................ 9-30
Figure 9-34: CPU Circuit..................................................................................................................................... 9-30
Figure 9-35: N-20 Main PCB Schematic Diagram............................................................................................. 9-30
Figure 9-36: N-20 Auxiliary PCB Schematic Diagram...................................................................................... 9-30
Figure 9-37: N-20 Flex Circuit Schematic Diagram .......................................................................................... 9-30
TABLES
Table 4-1: Microprocessor Error Codes............................................................................................................... 4-7
Table 8-1: Sensors................................................................................................................................................... 8-3

1-1
1 INTRODUCTION
1.1 Manual Overview
1.2 Warnings and Cautions
1.3 Description of the N-20 Portable Pulse Oximeter
1.1 Manual Overview
This manual contains service information for the Nellcor®portable pulse oximeter, models
N-20/N-20P, that is necessary to maintain and repair the N-20/N-20P by qualified service personnel.
Note that models designated for sale in Europe differ from models designated for sale in the USA only
in that the user control buttons and display use icons rather than alphabetical characters, and that the
product labels reflect the appropriate European certifications and company addresses.
1.2 Warnings and Cautions
"WARNING" is used to call attention to procedures that could result in an error in calibration or
performance, and/or precautions that are important to ensure the safety of both service personnel and
patients.
"CAUTION" is used to call attention to procedures that should be carefully followed to prevent
damage to the instrument.
1.3 Description of N-20 Portable Pulse Oximeter
The Nellcor portable pulse oximeters model N-20 (without printer) and N-20P (with printer) provide
noninvasive and continuous information about the percent of oxygen that is combined with
hemoglobin (SpO2) and pulse rate. A pulse amplitude indicator provides a qualitative indication of
pulse activity and patient perfusion. These instruments can be operated in either spot-check mode
(single-measurement), or extended-measurement mode (30 minutes of data). Patients are connected to
the instrument by a Nellcor oximeter sensor. The sensor LEDs are driven by the SpO2analog section,
which also conditions the incoming signals, and provides CPU adjustable gains stages. The CPU
measures the sensor's analog outputs, continually controls the gain stages, and calculates SpO2.
The N-20/N-20P is automatically calibrated each time it is switched on, and whenever a new sensor is
connected; it sets sensor-specific calibration coefficients by reading a calibration resistor in the sensor.
Also, the intensity of the sensor's light sources is adjusted automatically to compensate for differences
in tissue thickness and skin color.
Standard user controls consist of a Measure button and a Check-Battery button. The Measure button
signals the power control circuit to switch on the power supply. The power supply then provides
regulated power to the unit. Once power is on, the CPU reads both the Measure and Check-Battery
buttons for user commands.
The N-20P printer provides a hard copy of acquired patient measurements. The printer circuit
includes three user control buttons: ON (on/off), ADV (advance), and D/D (day/date). In addition, an
ambient temperature sensor is used with the battery voltage input to control printout quality.

2-1
2 ROUTINE MAINTENANCE
2.1 Overview
2.2 Cleaning
2.3 Periodic Safety and Functional Checks
2.4 Battery
2.1 Overview
The N-20/N-20P requires no routine maintenance, routine service, or calibration. If service is
necessary, contact qualified service personnel or Mallinckrodt’s representative. Use only
Mallinckrodt-approved test equipment when running a performance test on the N-20/N-20P. The
user's institution and/or local or national agencies may require testing.
2.2 Cleaning
Dampen a cloth with a commercial, nonabrasive cleaner, and lightly wipe the surfaces of the
N-20/N-20P. Do not spray or pour liquid on the instrument or accessories. Do not allow liquid to
contact connectors, switches, or openings in the chassis.
2.3 Periodic Safety and Functional Checks
The following checks should be performed at least every 2 years by a qualified service technician.
Inspect the exterior of the N-20/N-20P for damage.
Inspect safety labels for legibility. If the labels are not legible, contact Mallinckrodt Technical
Services Department or your local Mallinckrodt representative.
2.4 Battery
When the N-20/N-20P is going to be stored for 3 months or more, remove the battery prior to storage.
To replace or remove the battery, refer to Section 5, Disassembly Guide.