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.

3-1
3 PERFORMANCE VERIFICATION
3.1 Introduction
3.2 Required Materials
3.3 Performance Tests
Caution: Adhere to all testing instructions; failure to do so may damage the N-20/N-20P.
3.1 Introduction
This section describes performance verification for the N-20 and N-20P pulse oximeters (hereafter
called the “monitor”), following repairs. The N-20/N-20P are powered by alkaline batteries. The
N-20/N-20P design includes built-in electrical insulation; no ground resistance or electromagnetic
leakage testing is required.
The tests can be performed without removing the monitor cover. If the monitor fails to perform as
specified in any test, repairs must correct the discrepancy before the monitor is returned to the user.
3.2 Required Materials
Durasensor Nellcor DS-100A
Tester, Pulse Oximeter Nellcor SRC-2
3.3 Performance Tests
The N-20/N-20P will operate in conjunction with the Nellcor® pulse oximetry tester, model SRC-2,
to test instrument performance. The SRC-2 plugs into the DB-9 sensor connector and uses the
instrument's power supply and diagnostic software to test the display and the operation of the
instrument. Refer to the operator's manuals for the SRC-2 for details on performance testing with the
SRC-2.
Other tests, which are outlined below, include the display backlight test, the low battery indicator test,
the power-up self-test, and the thermal printer test (printer test applies only to N-20P).
3.3.1 Backlight Test
The electroluminescent backlight illuminates the display in three sections: (1) the main section, i.e.,
the Oxygen Saturation and Pulse Rate display fields, and the 14-segment pulse rate amplitude
indicator; (2) the Low Battery indicator, and (3) Pulse Search indicators each have their own
backlight. All backlights flash once during Power-On Self-Test.
The ambient light detector is located underneath a small circular window in the top right corner of the
N-20/N-20P display. Under low light conditions, the main section backlight is switched on. If a Low
Battery and Pulse Search indicator are lit, the monitor’s backlight is also lit.
To test for proper operation of the display backlight, observe the N-20/N-20P in a darkened room. If
any backlight section is not working correctly, contact Mallinckrodt's Technical Services Department
or Mallinckrodt's local representative for assistance.
3.3.2 Battery Performance
This test is provided to verify that the monitor will operate for the period specified.
The monitor is specified to operate on battery power as follows:

Performance Verification
3-2
N-20 (no printer) 37 hours with Alkaline batteries.
N-20/P (with printer) 32 hours with Alkaline batteries.
This test requires a new set of batteries. The new batteries must be installed after the test.
Connect the Nellcor SRC-2 pulse oximeter tester to the monitor.
Set the switches on the SRC-2 as follows:
Switch Setting
RATE 38
LIGHT LOW
MODULATION LOW
RCAL/MODE RCAL 63/LOCAL
Momentarily press the MEASURE button, and verify the following power-up sequence:
All indicators—OXYGEN SATURATION, PULSE RATE, PULSE SEARCH, LOW BATTERY,
and the PULSE BARS—light for a few seconds. Verify the OXYGEN SATURATION, and PULSE
RATE displays indicate "888.”
The OXYGEN SATURATION display momentarily indicates the monitor 3-digit software version.
The other displays are not lit.
Software versions may vary depending on the type of monitor and the date of manufacture.
The N-20P will display printer status immediately after displaying the software version. The
OXYGEN SATURATION display will indicate “Pr”and the PULSE RATE display will indicate
either “On” or “OFF.”
The OXYGEN SATURATION display momentarily indicates the letters ”tSt” and the monitor sounds
a single tone. The other displays are not lit. “tSt” verifies that the monitor recognizes that a tester is
connected.
The OXYGEN SATURATION and PULSE RATE displays indicate “0,” the PULSE SEARCH
indicator is flashing, and the PULSE BAR will start to register the simulated pulse.
After a few beats a pulse tone will be heard, and the PULSE SEARCH indicator will turn off. The
OXYGEN SATURATION display indicates between 79 and 83, and the PULSE RATE display
indicates between 37 and 39.
The monitor must operate for at least 37 hours if the printer is not turned on.
Verify that the LOW BATTERY indicator lights steadily sometime after 30 hours of operation.
Verify that the monitor turns off approximately 1 hour after the LOW BATTERY indicator starts
flashing.
Allow the monitor to continue operation until power-down due to low battery.
3.3.3 Power-Up Performance
Monitors with the same software must demonstrate identical startup routines. The power-up tests
verify the self-test function.
When an N-20/N-20P is switched on, a sequence of diagnostic tests is run that examines the
instrument electronics and display functions. This power-on self-test consists of the following events:
Immediately after power is switched on, the instrument simultaneously:
•Displays the number "8" in all six Oxygen Saturation and Pulse Rate display field segments;
•Illuminates all 14 pulse rate amplitude indicator segments;
•Illuminates the Pulse Search and Low Battery indicators; and

Performance Verification
3-3
•Illuminates the display backlight.
During the next few seconds, the instrument:
•Switches off the display backlight;
•Displays three digits in the Oxygen Saturation display field representing the software version (for
example, 123 is software version 1.2.3).
•Only the N-20P displays the printer status in the display fields; that is, either "Pr On" or "Pr OFF."
If a sensor is attached to the instrument, a zero ("0") appears in first position of the display fields. The
Pulse Search indicator flashes; if no sensor is attached to the instrument, horizontal dashes appear in
all six Oxygen Saturation and Pulse Rate display fields, and the Pulse Search indicator flashes.
After approximately 1 minute, a short beep occurs and the instrument automatically switches off.
If at any time during the test sequence "Err" followed by a code number is displayed, make a note of
the error code and refer to Section 4.7, Error Codes, for a description.
3.3.3.1 How To Run the Self-Test
Place a new set of batteries in the monitor.
Do not connect a sensor or SRC-2 to the monitor.
Momentarily press the MEASURE button, verify the following power-up sequence:
All indicators—OXYGEN SATURATION, PULSE RATE, PULSE SEARCH, LOW BATTERY,
and the PULSE BARS—light for a few seconds. Verify that the OXYGEN SATURATION and
PULSE RATE displays indicate "888."
The OXYGEN SATURATION display momentarily indicates the monitor 3-digit software version.
The other displays are not lit.
Software versions may vary depending on the type of monitor and the date of manufacture.
The N-20P will display printer status immediately after it displays software version. The OXYGEN
SATURATION display will indicate “Pr” and the PULSE RATE display will indicate either “On”or
“OFF.”
OXYGEN SATURATION and PULSE RATE display dashes (– – –) in each window, the monitor
sounds a single tone, and the PULSE SEARCH indicator is flashing. The other displays are not lit.
Verify that the monitor automatically turns off after 60 seconds.
If the Measure button was held down for more than 3 seconds (extended mode), the monitor will not
turn off after 60 seconds but will operate for approximately 3 minutes before automatically turning
off.
3.3.4 Printer Test
The following procedure applies to the N-20P only.
The SRC-2 must be used to test the operation of the N-20P printer and the printer's user-control
buttons. When an SRC-2 is plugged into the DB-9 connector, the N-20P does not respond to button
presses during Power-On Self-Test; however, it does acknowledge any button press after the self-test
with an immediate beep and the following display codes:
Button Press Display
Measure 9O
battery check bAt

Performance Verification
3-4
ON On
ADV Ad
D/D dd
combinations Err
1. Press the Measure button: "9O" appears in the Oxygen Saturation display.
2. Press the Battery-Check button: "bAt" appears in the Oxygen Saturation display.
3. Press the printer ON button: "On" appears in the Oxygen Saturation display. A
printer test pattern prints out; the following is an approximate example of the test
pattern:
Examine the test pattern to verify that all dots print with a uniform darkness. Overall printout
darkness can be adjusted; to adjust printer darkness, see paragraph 4.6.7. If printout darkness is
either irregular or dots are missing, contact Mallinckrodt's Technical Services Department or
Mallinckrodt's local representative for assistance.
1. Press the printer ADV button. “Ad” appears in the Oxygen Saturation display. Paper advances
one line for each button press.
2. Press the printer D/D button: "dd" appears in the Oxygen Saturation display.
3. End SRC-2 printer test.
3.3.5 Hardware and Software Tests
Hardware and software tests include the following:
Operation with a Pulse Oximeter Tester
Normal Operation
3.3.5.1 Pulse Oximeter Tester
1. Connect the Nellcor SRC-2 pulse oximeter tester to the monitor.
2. Set the switches on the SRC-2 as follows:
Switch Setting
RATE 38
LIGHT LOW
MODULATION LOW
RCAL/MODE RCAL 63/LOCAL
3. Momentarily press the MEASURE button, and verify the following power-up sequence:

Performance Verification
3-5
4. All indicators—OXYGEN SATURATION, PULSE RATE, PULSE SEARCH, LOW
BATTERY, and the PULSE BARS—light for a few seconds. Verify that the OXYGEN
SATURATION and PULSE RATE displays indicate "888.”
5. The OXYGEN SATURATION display momentarily indicates the monitor 3 digit software
version. The other displays are not lit.
6. Software versions may vary depending on the type of monitor and the date of manufacture.
The N-20P will display printer status immediately after software version display. The OXYGEN
SATURATION display will indicate “Pr,” and the PULSE RATE display will indicate either “On” or
“OFF.”
The OXYGEN SATURATION display momentarily indicates the letters ”tSt” and the monitor sounds
a single tone. The other displays are not lit. “tSt” verifies that the monitor recognizes that a tester is
connected.
The OXYGEN SATURATION and PULSE RATE displays indicate “0,” the PULSE SEARCH
indicator is flashing, and the PULSE BAR will start to register the simulated pulse.
After a few beats a pulse tone will be heard, and the PULSE SEARCH indicator will turn off. The
OXYGEN SATURATION display indicates between 79 and 83 and the PULSE RATE display
indicates between 37 and 39.
3.3.6.2 Normal Operation
These tests are an overall qualitative check of the system and require connecting a live subject to the
monitor:
Connect a DS-100A Sensor to monitor.
Place the DS-100A Sensor on the subject as recommended in the monitor Operator's Manual.
Press the Measure button for at least 5 seconds to turn on the monitor.
The monitor should stabilize on the subject's physiological signal in about 10 to 15 seconds. Verify
that the saturation value and pulse rate are acceptable.

Performance Verification
3-6
TEST RESULTS
Model: N-20 Serial:_____________________________
Date:___________Customer Name:________________________________
Description Pass Fail
Performance Tests _____ ____
Backlight Test _____ ____
Battery Performance _____ ____
Testing the Low Battery Indicator _____ ____
Power-Up Performance _____ ____
How to Run the Self-Test _____ ____
Printer Test _____ ____
Pulse Oximeter Test _____ ____
Normal Operation _____ ____
I certify that the monitor listed in this form has successfully passed all of these tests.
Technician:_________________________________________________Date:____________
I certify that the above signed technician has performed the tests listed on this form and the monitor performs
satisfactorily.
Support Center Manager:___________________________________________________Date:____________

4-1
4 TROUBLESHOOTING
4.1 How to Use This Section
4.2 Who Should Perform Repairs
4.3 Replacement Level Supported
4.4 Obtaining Replacement Parts
4.5 Troubleshooting Guide
4.6 Service Procedures
4.7 Error Codes
WARNING: Disassembly of the instrument exposes hazardous voltages. To avoid
injury or instrument damage, disassembly or maintenance must be attempted only by
qualified service personnel.
4.1 How to Use this Section
This section explains how to identify and correct monitor difficulties and provides procedures for
common service-related activities, such as battery replacement, clearing paper jams, and adjusting
printer darkness.
Use this section in conjunction with Section 3, Performance Verification, and Section 6, Spare Parts.
To remove and replace a part you suspect is defective, follow the instructions in Section 5,
Disassembly Guide. The functional circuit analysis, located in the Technical Supplement at the end of
this manual, offers information on how the device functions, as well as part locator diagrams and
detailed schematic diagrams.
4.2 Who Should Perform Repairs
Only qualified service personnel should open the device housing, remove and replace components, or
make adjustments. If your medical facility does not have qualified service personnel, contact
Mallinckrodt Technical Services.
4.3 Replacement Level Supported
The replacement level supported for this product is to the printed circuit board (PCB) and major
subassembly level. Once you isolate a suspected PCB, replace the PCB with a known good PCB.
Check to see that the trouble symptom disappears and the device passes all performance tests. If the
trouble symptom persists, swap the replacement PCB and the suspected malfunctioning PCB (the
original PCB that was installed when you started troubleshooting) and continue troubleshooting as
directed.
4.4 Obtaining Replacement Parts
Mallinckrodt Technical Services provides technical assistance information and replacement parts. To
obtain replacement parts, contact Mallinckrodt. Refer to parts by the part names and part numbers
listed in Section 6, Spare Parts.
4.5 Troubleshooting Guide
This section discusses potential symptoms, possible causes, and actions for their resolution. Should
this troubleshooting guide fail to address the symptoms evident in a particular N-20/N-20P, please

Troubleshooting
4-2
contact Mallinckrodt's Technical Services Department or a local Mallinckrodt representative for
assistance.
If the N-20/N-20P does not perform as expected:
•Check for proper sensor placement.
•Depending on concentration, indocyanine green, methylene blue, and other intravascular dyes
may affect the accuracy of a measurement.
•These instruments are calibrated to read oxygen saturation of functional arterial hemoglobin
(saturation of hemoglobin functionally capable of transporting oxygen in the arteries), and
significant levels of dysfunctional hemoglobins such as carboxyhemoglobin or methemoglobin
may affect the accuracy of a measurement.
If the electronics and/or display functions require testing, refer to Section 3, Performance Verification.
Symptom 1: No response to Measure button.
Cause Action
Battery access door may not be properly latched. Check access door and ensure it is properly
latched.
Batteries may be discharged. Exchange them for a new set.
Batteries may be incorrectly installed. Ensure that batteries are oriented according
to the polarity indicator.
Batteries may not be making proper electrical contact. Inspect contacts for deformity; clean contacts
to remove oxidization.
Fuse F1 on the auxiliary PCB may be open. See paragraph 4.6.5, Fuse Replacement.
Dust may have accumulated under Measure button causing
loss of electrical contact.
Clean contact points under Measure button
(see Section 5.3, N-20 Disassembly Guide).

Troubleshooting
4-3
Symptom 2: Pulse Search indicator appears for more than 5-10
seconds.
Cause Action
Sensor may be improperly positioned. Ensure the sensor is correctly applied (see
sensor directions for use).
Incorrect sensor may be in use. See sensor directions for use to ensure that
the patient's weight and sensor application is
correct. Test the sensor on another person to
verify proper operation.
Perfusion may be too low. Check patient status. Test the instrument on
someone else, or try another type of sensor.
The N-20/N-20P will not make a
measurement if perfusion is inadequate.
Foreign material on the sensor LEDs or photodetector may be
affecting performance.
Clean the test area and ensure that nothing
blocks the sensor site.
Patient motion may be interfering with the instrument's ability
to find a pulse pattern.
Environmental motion may be interfering with the
instrument's ability to track a pulse
The sensor may be too tight, there may be excessive
illumination (e.g., a surgical or bilirubin lamp or direct
sunlight), or the sensor may be placed on an extremity with a
blood pressure cuff, arterial catheter, or intravascular line.
If possible, ask the patient to remain still.
Verify that the sensor is securely applied and
replace it if necessary, move it to a new site,
or use a sensor that tolerates patient
movement, such as an appropriate adhesive
sensor.
The DB-9 sensor connector on the N-20/N-20P may be
broken.
Replace the DB-9 connector (Section 4.6.6).
Symptom 3: Pulse Search indicator appears after successful
measurements have been made.
Cause Action
Patient perfusion may be too low. Check patient status. Test the instrument on
someone else, or try another type of sensor.
The N-20/N-20P will not make a
measurement if perfusion is inadequate.
Patient motion may be interfering with the instrument's ability
to find a pulse pattern.
Environmental motion may be interfering with the
instrument's ability to track a pulse.
The sensor may be too tight, there may be excessive
illumination (e.g., a surgical or bilirubin lamp or direct
sunlight), or the sensor may be placed on an extremity with a
blood pressure cuff, arterial catheter, or intravascular line.
If possible, ask the patient to remain still.
Verify that the sensor is securely applied and
replace it if necessary, move it to a new site,
or use a sensor that tolerates patient
movement, such as an appropriate adhesive
sensor.
Symptom 4: Dashes (– – –) appear in the display.
Cause Action
The sensor is not connected to the instrument. Check all sensor connections; try substituting
another sensor. Check all extension cables. If
an extension cable is in use, remove it and
plug the sensor directly into the instrument.
Symptom 5: Pr Err is displayed during the Power-On Self-Test (N-20P only).

Troubleshooting
4-4
Cause Action
The printer is not operational, but the N-20P continues to
obtain patient measurements.
Check to see if the paper is jammed.
Examine the print head and ensure that it has
returned to the home position.
Symptom 6: Err followed by a number appears on the display.
Cause Action
See Section 4.7 for error codes. Record the number that is displayed.
Symptom 7: Time or date is incorrect (N-20P only).
Cause Action
The real-time clock (RTC) battery may be exhausted. Replace the RTC battery (see Section 4.6.4).
Reset the time and date (see Section 4.6.3).
Symptom 8: Printer fails to operate (N-20P only).
Cause Action
Fuse F2 on the auxiliary PCB may be open. See paragraph 4.6.5 for information about
fuses.
Symptom 9: Printer paper advances but instrument does not print (N-20P
only).
Cause Action
The thermal paper may be improperly loaded; characters can
be printed on only one side of the thermal paper roll.
Ensure that the thermal paper is properly
loaded; if needed, remove the roll of printer
paper and reload the printer paper.
Symptom 10: Paper mechanism jams (N-20P only).
Cause Action
Note: If a printer paper jam is detected during Power-On Self-Test, Pr Err may appear on the display.
Switch off the N-20P. Then check to see if
the print head is at the home position; if so,
attempt to pull the paper out by pulling
gently—do not force it.
If the print head is not at the home position,
and the paper cannot be easily pulled out
from the printer, then the printer may need to
be disassembled to remove the paper jam
(see Sections 5.3, N-20 Disassembly
Procedure, and 4.6.2, Loading/Clearing
Printer Paper).
4.6 Service Procedures
The following service procedures are most likely to be encountered by the service technician. The
PCB designation for a component appears in parentheses, for example, (BT1) or (U15).