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Mallinckrodt Nellcor N-20PA Service Manual

Portable pulse oximeter
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SERVICE MANUAL
N-20PA Portable Pulse Oximeter
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.
    2000 Mallinckrodt Inc. All rights reserved. 062153A-0500
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  • Page 1 N-20PA Portable Pulse Oximeter 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.
  • Page 2 4280 Hacienda Drive Pleasanton, CA 94588 USA Nellcor Puritan Bennett Inc. is a wholly owned subsidiary of Mallinckrodt Inc. Nellcor and Nellcor Puritan Bennett are trademarks of Mallinckrodt Inc. To obtain information about a warranty, if any, for this product, contact Nellcor Technical Services or your local Nellcor representative.

  • Page 3: Table Of Contents

    CONTENTS Contents................................... iii Figures..................................iv Tables ..................................v SECTION 1: Introduction............................1-1 1.1 Manual Overview............................1-1 1.2 Warnings, Cautions, and Notes........................1-1 1.3 Description of the N-20PA Portable Pulse Oximeter ...................1-1 SECTION 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 SECTION 3: Performance VERIFICATION.....................3-1 3.1 Introduction ..............................3-1...

  • Page 4: Figures

    CONTENTS 7.2 Repacking in Original Carton ........................7-1 7.3 Repacking in a Different Carton........................7-1 SECTION 8: Specifications..........................8-1 8.1 Performance..............................8-1 8.2 Alarms................................8-1 8.3 Electrical...............................8-2 8.4 Environmental...............................8-2 8.5 Physical.................................8-3 SECTION 9: Technical Supplement........................9-1 9.1 Introduction ..............................9-1 9.2 Functional Overview.............................9-1 9.3 Definition of Terms ............................9-5 9.4 Overall Block Diagram..........................9-6 9.5 SpO 2 Analog Circuitry ..........................9-6 9.6 Digital Circuitry............................9-12...

  • Page 5: Tables

    CONTENTS Figure 9-18: CPU Memory Circuit ......................... 9-17 Figure 9-19: Input Port Circuit..........................9-18 Figure 9-21: Real-Time Clock Circuit ........................9-19 Figure 9-22: Audio Output Circuit........................... 9-20 Figure 9-24: User Controls Circuit........................... 9-23 Figure 9-27: Analog Reference Voltage Circuit....................... 9-26 Figure 9-28: Ambient Light Circuit..........................
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  • Page 7: Section 1: Introduction

    SECTION 1: INTRODUCTION 1.1 Manual Overview 1.2 Warnings, Cautions, and Notes 1.3 Description of the N-20PA Portable Pulse Oximeter MANUAL OVERVIEW This manual contains information for servicing the N-20PA portable pulse oximeter. Only qualified service personnel should service this product. Before servicing the device, read the operator’s manual carefully for a thorough understanding of its operation.
  • Page 8 Section 1: Introduction 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, both the measure and check battery buttons are read by the CPU for user commands.

  • Page 9: Section 2: Routine Maintenance

    The following checks should be performed at least every 2 years by a qualified service technician. Inspect the exterior of the N-20PA for damage. Inspect safety labels for legibility. If the labels are not legible, contact Mallinckrodt Technical Services Department or your local Mallinckrodt representative. BATTERY When the N-20PA is going to be stored for 3 months or more, remove the battery prior to storage.
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  • Page 11: Section 3: Performance Verification

    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. Mallinckrodt recommends routine performance testing at 1-year intervals. Refer to the SRC-2 operator’s manual for details on performance...
  • Page 12 Performance Verification To enter the diagnostic mode, connect the SRC-2 to the N-20PA while the oximeter is off; then, turn the oximeter on. While in the diagnostic mode, a “d” is displayed in the leftmost segment of the display. Note: No alarms sound while in the diagnostic mode.
  • Page 13 Performance Verification 4. The monitor must operate for at least 37 hours with no printer activity. 5. Verify that the LOW BATTERY indicator lights sometime after 35 hours of operation. 6. Verify that the LOW BATTERY indicator starts flashing after 36 hours of operation.
  • Page 14 Performance Verification SRC-2 Settings Monitor Indications RATE LIGHT MODULATION HIGH1 HIGH 81+ 2 112+ 2% (110 - 114) 81+ 2 201+ 3% (195 - 207) HIGH 81+ 2 201+ 3% (195 - 207) 3.3.2.2 Adult Defaults and Alarm Limit Ranges The following procedure will allow verification of the monitor’s adult factory defaults, adjusting those defaults, and automatic reset to factory defaults.
  • Page 15 Performance Verification / min 5. Press the PRINTER ON button and reduce the High Saturation Alarm limit below the live subject’s value; typically 90 will be sufficient. 6. Momentarily press the DAY/DATE button and verify that the “90” in the display stops flashing and the “170”...
  • Page 16 Performance Verification 15. Press and hold the BATTERY CHECK button and then momentarily press the DAY/DATE (D/D) button on the top of the monitor. Verify that the following display is shown and that the “90” is flashing. / min 16. Momentarily press the DAY/DATE button and verify that the “90” in the display stops flashing and that the “190”...
  • Page 17 Performance Verification 21. Press the MEASURE button, and verify the following power-up sequence: a. 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."...
  • Page 18 Performance Verification / min 25. Momentarily press the DAY/DATA button and verify that the “85” in the display stops flashing and that the “40” Rate Default starts flashing. 26. Momentarily press the DAY/DATE button and verify that the monitor returns to the normal monitoring display and indicates the live subject’s saturation and pulse rate.
  • Page 19 Performance Verification d. The monitor will begin to track the pulse and after a few beats will display the subject’s Oxygen Saturation and Pulse Rate. 4. Press and hold the BATTERY CHECK button and then momentarily press the DAY/DATE (D/D) button on the top of the monitor. Verify that the following display is shown and that the “95”...
  • Page 20 Performance Verification 12. Momentarily press the DAY/DATE button and verify that the monitor returns to the normal monitoring display and indicates the live subject’s saturation and pulse rate. 13. Press and hold the BATTERY CHECK button and then momentarily press the DAY/DATE (D/D) button on the top of the monitor.
  • Page 21 Performance Verification 19. Momentarily press the BATTERY TEST button and verify that the alarm remains silent for 2 minutes and that the number representing the live subject’s saturation and pulse rate continues to flash. The alarm may be silenced as necessary for remainder of the test. 20.
  • Page 22 Performance Verification / min 25. Momentarily press the DAY/DATA button and verify that the “85” in the display stops flashing and that the “40” Rate Default starts flashing. 26. Momentarily press the DAY/DATE button and verify that the monitor returns to the normal monitoring display and indicates the live subject’s saturation and pulse rate.
  • Page 23 Performance Verification b. The OXYGEN SATURATION display momentarily indicates the monitor 3-digit software version. The other displays are not lit. Note: Software versions may vary depending on the date of manufacture. The N-20PA will display the letters “PA” in the PULSE RATE display while the software version is being displayed in the OXYGEN SATURATION display.
  • Page 24 Performance Verification To test for proper operation of the display backlight, observe the N-20PA in a darkened room. If any backlight section is not working correctly, contact Mallinckrodt’s Technical Services Department or your local Mallinckrodt representative for assistance. 3.3.5 Low Battery Test The N-20PA CPU monitors the battery voltage level and alerts the user via the Low Battery indicator when voltage is getting low.
  • Page 25 Overall printout darkness can be adjusted; to adjust printer darkness, see paragraph 0. If printout darkness is either irregular or dots are missing, contact Mallinckrodt’s Technical Services Department or your local Mallinckrodt representative for assistance. 4. Press the printer ADV button: “Ad” appears in the Oxygen Saturation display.
  • Page 26 Performance Verification TEST RESULTS Model: N-20PA Serial:_____________________________ Date:___________Customer Name:________________________________ Test # Description Pass Fail 3.3.1 Battery Performance ____ ____ 3.3.2 Power-Up Performance ____ ____ 3.3.2.1 Power-Up Self-Test ____ ____ 3.3.2.2 Adult Defaults and Alarm Limit Ranges ____ ____ 3.3.2.3 Neonate Defaults and Alarm Limit Ranges ____ ____ 3.3.3...

  • Page 27: Section 4: Troubleshooting

    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. TROUBLESHOOTING GUIDE Table 4-1 this section discusses potential symptoms, possible causes, and actions for their resolution.
  • Page 28 Troubleshooting If the N-20PA does not perform as expected, the problem may be related to the following: • Incorrect sensor placement. • Depending on concentration, indocyanine green, methylene blue, and other intravascular dyes may affect the accuracy of a measurement. •...
  • Page 29 Mallinckrodt does not recommend using a sensor on the same limb as these three devices. 8. Replace the DB-9 connector.
  • Page 30 Troubleshooting Dashes (- - -) appear in The sensor is not connected Check all sensor the display. to the instrument. 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.
  • Page 31 Troubleshooting 4.7.1 Installing Batteries The N-20PA operates on four 1.5-V alkaline “C” cell batteries. Do not use off-the-shelf rechargeable batteries; this type of battery can cause the Low Battery indicator to be inaccurate. To install the batteries: 1. Remove the battery access door by pressing the battery compartment access door latch.
  • Page 32 Troubleshooting 3. When dashes appear in the Oxygen Saturation and Pulse Rate displays, press the D/D (day/date) button once. At this point, the Oxygen Saturation display shows “txx”, with “t” representing time; “xx” representing hours, and “yy” representing minutes. Note that “xx” (hours) is flashing. 4.
  • Page 33 Troubleshooting 6. Reset the clock (see paragraph 4.7.3, Setting Date and Time). 4.7.5 Replacing Fuses Two fuses (F1 and F2) are located on the auxiliary PCB. Fuse F1 may open to protect the CPU and its associated components from damage if the power supply malfunctions.
  • Page 34 3-digit error code number appears in the Pulse Rate display. If an error message appears, record the error code number. Match the number to the description in the following table, and contact Mallinckrodt’s Technical Services Department or your local Mallinckrodt representative for assistance.
  • Page 35 Troubleshooting Category 1 — Microprocessor Errors Errors in the CPU (main PCB). Likely action is replacement of the CPU. Error in internal RAM register test Error in zero register test Error in register contents clearing test Error in register contents increment test Error in register contents decrement test 106–109 Errors in logical operations test...
  • Page 36 Troubleshooting Category 6 — Clock Errors Failure of the real-time clock (auxiliary PCB), or timing differences between the CPU clock and the real-time clock. Likely action is replacement of the main or auxiliary PCB. Failure of real-time clock 602, 603 Errors in real-time clock Category 7 —...

  • Page 37: Section 5: Disassembly Guide

    SECTION 5: DISASSEMBLY GUIDE 5.1 Introduction 5.2 Beginning Disassembly 5.3 N-20PA Disassembly Procedure INTRODUCTION The device can be disassembled down to all major component parts, including: • PCBs • batteries • cables • chassis enclosures Tools required: • small, Philips-head screwdriver •...

  • Page 38: Figure 5-2: N-20Pa Covers With The Pcb And Display Assembly

    Section 5: Disassembly Guide 1. Remove the battery door (19) and batteries. 2. Remove the sensor lock (34) by lightly pressing in on its ears and pulling out from the sensor shroud. 3. Remove the paper door (20), paper roll, and the printer door (21). 5.2.1 Removing the Covers Figure 5-2: N-20PA Covers with the PCB and Display Assembly...

  • Page 39: Figure 5-3: Main, Auxiliary, And Display Pcb Assembly

    Section 5: Disassembly Guide 2. Separate the front cover (16) from the rear battery cover by wedging a thin flat-head screw driver between the covers at the base of the instrument and slowly prying them apart. Note: The covers are hinged at the top end in a different way; do not attempt to separate the covers using this technique at the top of the instrument.

  • Page 40: Disassemblying The Printer/Flex Circuit Assembly

    Section 5: Disassembly Guide DISASSEMBLYING THE PRINTER/FLEX CIRCUIT ASSEMBLY Figure 5-4: Printer and Flex Circuit Assembly Figure 5-4 shows how to disassemble the printer and flex circuitry. 1. Remove the printer button stiffener (37). 2. Disconnect the two flex-circuit headers of the printer (29) from the connectors on the printer flex circuit (28) by slowly pulling them outward from side to side at alternating ends of the connectors.

  • Page 41: Section 6: Spare Parts

    SECTION 6: SPARE PARTS 6.1 Introduction 6.2 Spare Parts List INTRODUCTION Spare parts, along with corresponding part numbers, are shown below. To order replacement parts, contact Mallinckrodt’s Technical Services Department and order by part number. SPARE PARTS LIST Item Designator...
  • Page 42 Spare Parts Item Designator Description Door, printer 026338 Fuse, micro, 1 amp (auxiliary PCB) 691236 Fuse, micro, 1.5 amp (auxiliary PCB) 691239 Insulator, printer 026139 Item Designator Description Nut, keps, SS, 4-40 851101 PCB, auxiliary 024472 PCB, main 024468 Printer flex circuit 024464 Printer 024462...

  • Page 43: Section 7: Packing For Shipment

    GENERAL INSTRUCTIONS Pack the monitor carefully. Failure to follow the instructions in this section may result in loss or damage not covered by the Mallinckrodt warranty. If the original shipping carton is not available, use another suitable carton or call Mallinckrodt Technical Services to obtain a shipping carton.
  • Page 44 [Page intentionally left blank]...

  • Page 45: Section 8: Specifications

    SECTION 8: SPECIFICATIONS 8.1 Performance 8.2 Alarms 8.3 Electrical 8.4 Environmental 8.5 Physical PERFORMANCE 8.1.1 Range Saturation 0–100% Pulse Rate 20–250 beats per minute (bpm) 8.1.2 Accuracy Adults 70–100% ± 2 digits 0–69% unspecified Neonates 70–95% ± 2 digits 0–69% unspecified Pulse rate 20–250 bpm ±...

  • Page 46: Electrical

    Section 8: Specifications 8.2.2 Factory Default Alarm Settings Adult Neonate Upper Limit: 100% Lower Limit: PR Upper Limit: 170 bpm 190 bpm PR Lower Limit: 40 bpm 90 bpm ELECTRICAL 8.3.1 Battery Type Four alkaline “C” size batteries Battery Capacity Typically 32 hours with four alkaline “C”...

  • Page 47: Physical

    Section 7: Specifications PHYSICAL 8.5.1 Weight (with batteries installed) 0.6 kg (1.3 lb) 8.5.2 Size 19.0 cm high × 7.6 cm wide × 6.35 cm deep (7.5 in. × 3.0 in. × 2.5 in.)
  • Page 48 [Page intentionally left blank]...

  • Page 49: Section 9: Technical Supplement

    SECTION 9: TECHNICAL SUPPLEMENT 9-1 Introduction 9-2 Functional Overview 9-3 Definition of Terms 9-4 Overall Block Diagram 9-5 SpO Analog Circuitry 9-6 Digital Circuitry 9-7 Circuitry Illustrations INTRODUCTION This Technical Supplement provides the reader with a discussion of the N-20PA circuits.
  • Page 50 Technical Supplement • Analog Block Diagram (Figure 9-2) — Analog circuitry has high signal sensitivity and reduced susceptibility to noise. Its design allows for a wide range of input signal levels and a broad range of pulsatile modulation. The SpO analog circuit consists of four subsections: 1.

  • Page 51: Figure 9-3: N-20Pa Hardware Block Diagram

    Technical Supplement Analog Ambient Battery Ambient Reference Light Voltage Temperature Voltage Analog Battery Serial Power Interface Control Power SpO2 Power Patient Analog Analog Control Sensor Control AD Bus Section Power Control Address Address Demultiplexing Decoding Power Supply AD Bus Enables Standard User Supply...

  • Page 52: Figure 9-4: Power Supply Block Diagram

    Technical Supplement On/Off button AUX PCB Main PCB +5 VDC Microprocessor Power shutoff Power Power Disposable +70 VDC circuits control supply Display drivers batteries (fuse; 4–6 VDC circuits circuits AUX PCB EMI protect; AUX PCB ESD protect) Display backlight –5 VDC +12 VDC Analog section...

  • Page 53: Definition Of Terms

    Technical Supplement Main PCB AUX PCB Printer Printer flex Microprocessor Printer interface circuit User push buttons Figure 9-6: Printer Control Block Diagram DEFINITION OF TERMS Analog to Digital (A/D) converter. The CPU has a 10-bit A/D converter on board. Up to eight different analog inputs can be provided to the A/D converter for measurement.

  • Page 54: Overall Block Diagram

    Technical Supplement OVERALL BLOCK DIAGRAM Exclusive of covers, buttons, and external connectors, the N-20PA consists of three main components: the main PCB, the auxiliary PCB, and the display assembly and analog shield. • Main PCB — Contains the SpO analog circuitry; the CPU; support memory circuits;...

  • Page 55: Figure 9-7: Spo2 Analog Circuitry Block Diagram

    Technical Supplement The relationship of these subsections is shown in Figure 9-7. Input signal Signal gain AC Ranging Patient conditioning sensor photocurrent variable gain, offset to voltage filtered for substraction; conversion LEDs each LED additional gain demutiplexed channel and filtering to 2 channels Main PCB Main PCB...
  • Page 56 Technical Supplement The IR and red LEDs are separately controlled with their drives currents multiplexed over two shared wires. Current to the IR LED is in the range of 4.3-50.0 mA; and, current to the red LED is in the range of 6.5-75.0 mA. Currents are limited to less than 100 mA for two reasons: (1) slight excess current can potentially change the emission characteristics of the LEDs, and (2) large excess current could create excessive heat at the sensor site.

  • Page 57: Figure 9-9: Differential Synchronous Demodulation Circuit

    Technical Supplement TP78 R159 88.7K VREF +12V 2.0K R160 LT1097 51.1K R158 SAMPRED 88.7K SAMPIR OFF/ON LTC201 VREF LF444 390PF TP49 3.32K 82.5K 18PF 3.32K +12V LTC201 .47UF 280K 182K .047UF VREF 3.32K VREF LF444 R157 511K LTC201 .047UF 3.32K LTC201 .47UF TP44...

  • Page 58: Figure 9-11: Variable Gain Circuit

    Technical Supplement If the instantaneous average photocurrent (DC offset) is excessive and U1D cannot bring it to VREF, the PHOTOI line to the CPU (HSI0) is activated. This action is an indication of excess ambient light into the photosensor, or the occurrence of excess noise in the input circuit.

  • Page 59: Figure 9-12: Filtering Circuit

    Technical Supplement The two variable gain circuits are functionally equivalent. The gain of each circuit is contingent upon the signals received level and is controlled to bring each signal to approximately 3.5 V. Each circuit uses an amplifier and one switch in the triple SPDT analog multiplexing unit U2.

  • Page 60: Digital Circuitry

    Technical Supplement 9.5.4 AC Ranging In order to achieve a specified level of oxygen saturation measurement and to still use a standard-type combined CPU and A/D converter, the DC offset is subtracted from each signal. Because the DC portion of the signal can be on the order of one thousand times the AC modulation, 16 bits of A/D conversion would otherwise be required to accurately compare the IR and red modulations between the combined AC and DC signals.

  • Page 61: Figure 9-14: Digital Circuitry Block Diagram

    Technical Supplement • System memory — System memory is external to the CPU and consists of an 8K × 8 static RAM and a 64K × 16 EPROM. • Real-Time Clock (RTC) — The RTC keeps track of date and time, which is printed on each printout.
  • Page 62 Technical Supplement The CPU is capable of running up to 16 MHz; however, it is run at 10 MHz for decreased power consumption. All unused inputs are tied to either Vcc or ground through resistors—this prevents unused inputs floating to any voltage and causing excess power drain.

  • Page 63: Figure 9-16: Address Demultiplexing Circuit

    Technical Supplement ADDRESS DEMUX TP39 74HC573 R108 AD10 AD11 AD12 AD13 AD14 AD15 TP40 74HC573 R109 Figure 9-16: Address Demultiplexing Circuit U13 and U33 are transparent latches that latch the address portion of the AD bus data on the falling edge of ALE; the outputs are always enabled. The outputs of U13 and U33 are always the address portion of the AD bus.

  • Page 64: Figure 9-17: Address Decoding Circuit

    Technical Supplement EXINEN EXOUTEN 20 HDR ADDRESS DECODING TO: N-20 AUX PCB DC00-DFFF 74HC138 U30A E000-FFFF RAMEN 74HC10 TP74 U30B U30C 0000-DBFF ROMEN 74HC10 74HC10 TP71 R134 Figure 9-17: Address Decoding Circuit U30B and U28 are used to generate the input port and output port active low enable signals EXINEN and EXOUTEN.
  • Page 65 Technical Supplement U30C generates the EPROMs active low enable signal, ROMEN. The active low signals RAMEN and EXINEN are basically used as EPROM disable signals. When RAMEN or EXINEN or test point TP71 are low, the output of U30C, ROMEN, is forced high, disabling the ROM. Therefore, the EPROM is disabled for the range DC00-FFFF and enabled for the 55 Kbyte address range of 0h-DBFF.
  • Page 66 Technical Supplement The program that the CPU runs is stored in U15. U15 is a 16-bit wide output, one-time programmable (OTP) EPROM. During 16-bit wide bus accesses, the CPU uses address line A0 for low/high byte selection. A0 is not used as a normal address line.
  • Page 67 Technical Supplement The signal PR_STROBE controls U17’s output drivers. Under normal operation, the outputs are tristated and resistors R148-R154 pull the outputs low. PR_STROBE is driven low to turn on the output drivers of U17. Signals PR_DOT0-PR_DOT6 (pins Q1-Q7) drive the 7 print dots of the optional printer. PR_STROBE pulses all 7 of the dot lines for a specific time period (see also Printer Interface, Section 6.14).
  • Page 68 Technical Supplement Crystal Y1 provides an accurate 32.768 KHz clock input whenever the timekeeping circuitry of U29 is activated. The CPU only enables the timekeeping function when an optional printer is installed. If no printer is installed, the CPU switches off timekeeping, thereby extending battery life. Also, with no printer installed, the RTC clock is only used during diagnostic testing to verify the CPU clock timing.
  • Page 69 Technical Supplement • High Voltage Control Circuit (auxiliary PCB) — The high-voltage control circuit allows the CPU to switch on or off the display’s high-voltage input. 9.6.5.1 Control Conditioning Circuit The CPU generates a 400 µs low-pulse train at a 160 Hz rate on signal DISP_PHASE.
  • Page 70 Technical Supplement 9.6.6 Standard User Controls The user-controls circuit is illustrated in Figure 9-24. The standard user controls consist of two momentary push-button switches (On/Off and battery-check). The Of/Off button is an elastomeric contact switch, and the battery-check button is a mechanical momentary switch. The CPU input lines BAT_BTN and GO_BTN are normally pulled to the high state by R71 and R78.
  • Page 71 Technical Supplement TP72 GO BTN R102 TEST VCON To U21 pin 4 GO_BTN 150K TO: N-20 MAIN PCB 3.32K .01UF JP18 GO_SW TP71 C123 TEST 100PF CHECK BATTERY 150K TP88 TP81 BAT_BTN TEST TEST C126 100PF .01UF TO: N-20 AUX PCB GO_SW MEASURE BUTTON...
  • Page 72 Technical Supplement • Power shutoff circuit — This circuit controls power to all circuits except the power control circuit. In addition, a fuse protects the power supply from excessive current draw. The power supply is also protected against electrostatic discharge and electromagnetic interference. •...
  • Page 73 Technical Supplement 9.6.7.2 Power Shutoff Circuit This circuit is illustrated in Figure 9-25, Power Supply Circuit. Fuse F1 protects the unit from excessive current draw. CR24 protects against large voltage transients caused by ESD, EMI, and so on. Q15 is a dual-channel FET; the drain of Q15 part 2 (pin D2) is connected to battery ground;...
  • Page 74 Technical Supplement 9.6.7.5 High Voltage Supply This circuit is illustrated in Figure 9-25, Power Supply Circuit. The batteries (VBAT) provide the input power for the high-voltage supply. The high-voltage supply is a switched-inductor voltage regulator (U26) that operates in conjunction with a capacitive voltage doubler to output 72 VDC ± 5%. To protect against a runaway voltage condition, CR25 clamps U26 output to a safe level.
  • Page 75 Technical Supplement 9.6.9 Ambient Light The ambient light circuit is illustrated in Figure 9-28. LIGHT SENSOR VTB8442B MMBTA13L TP72 2.2M R136 33.2K .01UF Ambient Light Figure 9-28: Ambient Light Circuit Diode D8 is a photodiode that is used to measure ambient light. Q8, R68, and R136 provide current gain for D8’s photocurrent.
  • Page 76 Technical Supplement 9.6.11 Battery Voltage The battery voltage circuit is illustrated in Figure 9-30. VBAT TP73 15.8K BATTERY BAT_VOLT VOLTAGE SENSE 47.5K .01UF Figure 9-30: Battery Voltage Circuit The analog input voltage range of the CPU is 0-5 VDC. Because the battery voltage may be as high as 6.2 V, R69 and R70 form a voltage divider to decrease the measured battery voltage to a usable level.
  • Page 77 Technical Supplement The nominal voltages and voltage discharge curves are significantly different between rechargeable and disposable batteries. In order for the CPU to predict how much “battery life” remains, the nominal voltage and discharge curves must be known; the BAT_TYPE signal provides that information 9.6.13 Printer Control Printer circuitry is divided into two subsections: the printer interface and the printer flex circuit.
  • Page 78 Technical Supplement Inside the print head are seven resistors that heat up when power is applied, and in turn create dark dots on the thermal paper. One lead of the print-head resistors is connected to the printer supply voltage VPRN; the other lead is connected to the driver chip (see “Optional Printer Flex Circuit with User Controls”).

  • Page 79: Circuit Illustrations

    Technical Supplement The large bulk capacitor C3 is required due to the large current spikes that are required by the printer and the large internal series resistance of disposable batteries. Bulk capacitance is required to lessen the battery voltage drop caused by the current spikes.
  • Page 80 PWM2 SENSOR PWM1 INPUT LED DRIVE VREF .1UF R135 MMBTA56 TP45 3.74K 4.7PF 280K MMBTA56 LT1013 TP83 C116 C117 C118 100K DB9F 100PF 100PF 100PF TP47 TP46 MMBTA06 .1UF 182K .1UF TP50 4053 .022UF C119 VREF TP84 22.1K 100PF TP48 100K .1UF 6.04K...
  • Page 81 OFF/ON (HSO.1) /SAMPIR (HSO.2) /SAMPRED (HSO.0) IR/RED (P1.1) -60µS -60µS µS 105.6 158.4 177.6 283.2 336.0 337.2 443.2 496.0 515.2 620.8 673.6 State Time Figure 9-10 N-20PA HSO Timing Diagram 9-35...
  • Page 82 LTC201 LTC201 U11B U11A REDLED/AV From U2 pin 3 IRLED/AV REDDC 3.32K +5.7 .01UF TP54 .01UF 3.32K REDAC 3.32K LMC6044 .1UF .47UF TP55 .015UF 100K U11C .01UF LTC201 34.8K 3.32K VREF PWM1 12.1K TP56 LMC6044 TP85 47.5K .1UF TP57 4053 REDLED/AV PWM0 100K...
  • Page 83 VREF PR_HEAD1 VREF T2CLK/P2.3 PR_HEAD2 ANGND T2RST/P2.4 REDDC REDLED/AV ACH0/P0.0 P2.6/T2U-D REDAC /ZERO ACH1/P0.1 P2.7/T2CAPT IRDC PHOTOI ACH2/P0.2 HSI0 IRAC ACH3/P0.3 HSI1 RSENS DISP_PHASE ACH4/P0.4 HSI2/HSO4 R137 AMB_LIGHT PR_STROBE ACH5/P0.5 HSI3/HSO5 BAT_VOLT SAMPRED ACH6/P0.6 HSO0 PR_TEMP OFF/ON ACH7/P0.7 HSO1 PR_TACH SAMPIR EXTINT/P2.2 HSO2...
  • Page 84 EX_OUT LSB DISP_DATA DISP_CLK RTC_CLK RTC_RST PR_MOTOR PR_MEAS BEEP_1 BEEP_2 EXOUTEN R132 74HC574 150K TP82 TEST EX_OUT MSB PR_DOT6 PR_DOT5 AD10 PR_DOT4 AD11 PR_DOT3 AD12 PR_DOT2 AD13 PR_DOT1 AD14 PR_DOT0 AD15 RTC_IO EXOUTEN PR_STROBE R148 74HC574 R149 R123 150K 150K R150 150K R151...
  • Page 85 DISP_POL DISPLAY DRIVERS DISP_DL VDISP TP80 TEST DISP_DATA +70V DISP_PHASE DISP_CLK LATCH +70V TALIQ COLD SWITCH DOUT R113 4.75K MMBT5401L VDISP R116 390PF OSCIN MMBT5551L R115 OSCOUT 390PF R117 2N3904 6.19K 475K R114 MMBT5551L 12.1K HDR 32 SI9530 LATCH DOUT DISPLAY PS CTRL SET1 DISP_POL...
  • Page 86 BATTERY INPUT BATT GND TO CENTER MOUNTING HOLE TEST R155 POWER SUPPLY VBAT BATT PLUS TEST 1.5A R134 C116 C117 ILIM 22UF 22UF 22UF CR24 100PF 0.1UF 100K GATE TRANZORB 120UH 100K SI9405DY 22UF .1UF SI9956DY CR13 LT1173 C118 C119 31.6K 130T3 RAW-5V...
  • Page 87 VCON LT1046 CR11 TP84 VBAT TEST 1N914 TP72 R102 0.1UF TEST VCON VCON SET1 GO_BTN PWR_ON 150K TO: N-20 CLK1 RST1 MAIN PCB TP83 3.32K TEST SET2 VCON .01UF JP18 GO BTN CLK2 GO_SW RST2 R110 475K TP71 C123 TEST 74HC74 3.32K C110...
  • Page 88 ON BTN DD BTN ADV BTN PR_PRESENT VPRN R143 U36B PR_HEAD1 14.0K LT1017CS TP78 TEST VPRN R144 R146 1.24K TP79 U36A PR_HEAD2 TEST LT1017CS R145 60.4K VPRN TP77 TEST R106 R142 TO PRINTER PCB 150K 2N3904 TP35 TP36 TP37 150K TEST TEST TEST...
  • Page 89 TO N-20 AUX BOARD VPRN JP10 SEIKO HEADER 6 DOT4 MTP102-16 JP11 PRINTER OUTM PR_DOT6 DOT6 DOT6 OUT0 DOT5 OUT1 PR_DOT5 DOT4 OUT2 DOT3 OUT3 PR_DOT4 DOT2 OUT4 DOT1 OUT5 PR_DOT3 DOT0 OUT6 PR_DOT2 HEADER 8 PR_DOT1 LB1256 PR_DOT0 PR_MOTOR 3300UF ON OFF BUTTON PWR_ON...
  • Page 90 BATTERY INPUT BATT GND TO CENTER MOUNTING HOLE TEST R155 POWER SUPPLY VBAT BATT PLUS TEST 1.5A R134 C116 C117 ILIM 22UF 22UF 22UF CR24 .1UF 100K CR27 GATE TRANZORB 1N914 120UH SI9405DY 100K 100PF 22UF R100 SI9956DY .1UF VRECHARGE LT1173 TEST R101...
  • Page 91 TO N-20 POWER SUPPLY BOARD VPRN JP10 SEIKO HEADER 6 DOT4 MTP102-16 JP11 PRINTER OUTM PR_DOT6 DOT6 DOT6 OUT0 DOT5 OUT1 PR_DOT5 DOT4 OUT2 DOT3 OUT3 PR_DOT4 DOT2 OUT4 DOT1 OUT5 PR_DOT3 DOT0 OUT6 HEADER 8 PR_DOT2 PR_DOT1 LB1256 PR_DOT0 PR_MOTOR 3300UF ON OFF BUTTON...
  • Page 92 LIGHT SENSOR TO: N-20 SpO2 ANALOG DIGITAL SECTION AUX PCB VTB8442B GO_SW TP78 MMBTA13L TP72 +12V +12V R159 2.2M PR_HEAD1 GO BUTTON R136 88.7K C124 C125 VREF +12V +12V 33.2K PR_HEAD2 .01UF .1UF .1UF VREF PR_STROBE TANT C122 LTC201 LTC201 2.0K ACROSS U35 22UF...

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