Novametrix 860 Service manual

®

TCO2 M

Transcutaneous CO2/O2 Monitor

Service Manual

Model 860

May 16, 1997

Catalog No. 6590-90-00

Novametrix Medical Systems Inc.

5 Technology Drive

Wallingford, Connecticut, U.S.A. 06492.

Copyright 1997. All rights reserved. No part of this manual may be reproduced without the written permission of

Novametrix Medical Systems Inc. Printed in U.S.A.

R Revision History

16-May-97 Release at revision 00.

This document contains information which is proprietary of Novametrix Medical Systems, Inc., and may
not be reproduced, stored in a retrieval system, translated, transcribed or transmitted, in any form, or by any
means, without the prior explicit written permission of Novametrix Medical Systems Inc.

Novametrix reserves the right to change specifications without notice. TCO
trademarks, and NovaCARD and NovaCOM are trademarks of Novametrix Medical Systems Inc.

Rev. 00 Model 860 Service Manualiii

M and NOVADISK are registered

2

iv

[This page intentionally blank.]

Model 860 Service Manual Rev. 00

G Guarantee

Equipment manufactured or distributed by Novametrix Medical Systems Inc., is fully
guaranteed, covering materials and workmanship, for a period of one year from the date of
shipment, except for certain disposable products and products with stated guarantees other than
one year. Novametrix reserves the right to perform guarantee service(s) at its factory, at an
authorized repair station, or at the customer’s installation.

Novametrix’ obligations under this guarantee are limited to repairs, or at Novametrix’ option,
replacement of any defective parts of our equipment, except fuses, batteries, and calibration
gasses, without charge, if said defects occur during normal service.

Claims for damages during shipment must be filed promptly with the transportation company.
All correspondence concerning the equipment must specify both the model name and number,
and the serial number as it appears on the equipment.

Improper use, mishandling, tampering with, or operation of the equipment without following
specific operating instructions will void this guarantee and release Novametrix from any further
guarantee obligations.

Service Department

For factory repair service, call toll free

1-800-243-3444

In Connecticut, call Collect [phone]

FAX [phone]

http://www.novametrix.com

Email [e-mail]

Caution: Federal (U.S.A.) law restricts this device to sale, distribution, or use by or on the order
of a licensed medical practitioner.

Copyright
which is proprietary and the property of Novametrix Medical Systems Inc., and may not be
reproduced, stored in a retrieval system, translated, transcribed, or transmitted, in any form, or
by any means, without prior explicit written permission from Novametrix Medical Systems Inc.

Rev. 00 Model 860 Service Manualv

 1997, Novametrix Medical Systems Inc. This document contains information

vi

Service Policy

Novametrix Medical Systems Inc. will provide Warranty Service Support to its customers
within 48 hours of receiving a telephone request for technical support. This 48 hour period
begins once a service request is placed through the Factory Technical Support Department in
Wallingford, Connecticut. Novametrix provides factory direct technical support to its customers
through a technical support group located in Wallingford, Connecticut and company service
representatives located throughout the United States. All Technical Support for Novametrix
products is provided “Factory Direct”.

Novametrix provides 24 hour a day technical support accessibility via telephone numbers (800)
243-3444 or [phone]. After hours technical support requests (before 8:00 AM and after
5:00 PM Eastern Time) will be responded to promptly by the Technical Support On-Call staff.
It is suggested that any person calling in for technical support have the inoperative equipment
available for preliminary troubleshooting as well as product identification. Novametrix reserves
the right to repair or replace any product found to be defective during the warranty period.
Repair may be provided in the form of replacement exchange parts or accessories, on-site
technical repair assistance or complete system exchanges. Repairs provided due to product
abuse or misuse will be considered “non-warranty” and invoiced at the prevailing service rate.
Any replaced defective material is expected to be returned to Novametrix within 10 days of
being provided in order to avoid additional charges. Exchanged material should be returned
promptly and directly to Novametrix using the return paperwork and shipping label(s) provided.
Transferring return materials to local sales or dealer representatives does not absolve return
responsibility.

Novametrix manufactures equipment that is generally “user serviceable” and can usually be
repaired with the replacement of a plug-in electro-mechanical assembly by the clinical end user.
When repair parts are provided, the recipient can call into Novametrix for on-line replacement
assistance and repair assurance. In the event a replacement part requires increased technical
capability, Technical Support may request Biomedical assistance, provide on-site technical
support or complete replacement equipment. If the customer requires the return of their original
product, the exchange material will be considered “loaner material” and exchanged again after
the customer equipment is repaired.

Novametrix promotes customer participation in warranty repairs should they become necessary.
This program allows for customer training and a smooth transition into self-maintenance after
warranty, which can provide substantial cost savings on repairs throughout the product’s life.

The Novametrix Technical Support Department can provide technical product support at a level
appropriate to most customers protocol and budget requirements. Please contact the Technical
Support Group at Novametrix for additional information.

Additional Novametrix Technical Support Programs

• Focus Series Technical Training Seminars

• Test Equipment and Test Kits

• Service Contract / Part Insurance Plans

• On-Site Technical Support

• 24 hr. telephone support

• “Demand Services”
Flat rate parts-exchange,
Flat rate return for repair
Time and Material,
Full warranty, discounted replacement sensors

Model 860 Service Manual Rev. 00

C Contents

Section1 Safety .............................................................................................................1

Patient Safety ..............................................................................................................1

Contraindications ........................................................................................................1

Section2 Description ....................................................................................................3

Conventions ................................................................................................................4

Summary of Operation ................................................................................................4

Front and Rear Illustrations .........................................................................................5

Symbols ......................................................................................................................6

Section3 Theory of Operation .....................................................................................7

2726 Power Supply Board ..........................................................................................7

AC Mains and Battery Operation Overview ..................................................................... 7

AC Operation ...................................................................................................................7

2533 CPU Interface Board ..........................................................................................8

Power On/Off Control Circuitry ........................................................................................8

Power Supplies ............................................................................................................... 9

Precision Reference Supplies .........................................................................................9

Low Battery Voltage Shutdown .......................................................................................9

Microprocessor ..............................................................................................................10

Memory .........................................................................................................................10

Real Time Clock (RTC) .................................................................................................10

Sound generator ............................................................................................................11

Keypanel Interface ........................................................................................................11

Display Interface ............................................................................................................11

I/O Device Controller .....................................................................................................12

Watchdog Timer ............................................................................................................12

RS232 Serial Communication .......................................................................................12

Calibrator Control ..........................................................................................................13

Barometric Pressure ......................................................................................................13

Analog to Digital Conversion .........................................................................................13

Temperature Control .....................................................................................................14

Battery Voltage Monitoring ............................................................................................14

2534 Front End Board ...............................................................................................14

Sensor Temperature Monitoring ....................................................................................14

Sensor Heater Control ...................................................................................................14

Software Heater Shutdown Control ...............................................................................15

Sensor Temperature Fault Monitoring ...........................................................................15

Sensor Heater Power- Local Power ..............................................................................16

Sensor Identification ......................................................................................................16

Sensor Oxygen Value Measurement ............................................................................17

Sensor Carbon Dioxide Value Measurement ................................................................17

Multiplexor .....................................................................................................................17

Rev. 00 Model 860 Service Manualvii

viii

Section4 Maintenance ................................................................................................ 19

Cleaning and Disinfecting .........................................................................................19

Monitor/Calibrator .......................................................................................................... 19

Sensors ......................................................................................................................... 19

Calibrator ....................................................................................................................... 19

TCO2M Calibrator, Model 868 ..................................................................................20

Setting up the Calibrator ............................................................................................... 20

Disconnecting Gas Cylinders ........................................................................................ 21

Connect the calibrator ................................................................................................... 21

Battery Maintenance .................................................................................................21

Fuses ........................................................................................................................22

Changing AC Mains Voltage .....................................................................................23

Assembly Exchanges ................................................................................................25

Internal Assemblies .......................................................................................................25

Front End and CPU - Interface/Keypanel Assembly ..................................................... 25

Replacing the internal battery ....................................................................................... 26

Changing System Software ...................................................................................... 26

Barometric Pressure .................................................................................................27

Section5 Troubleshooting ......................................................................................... 29

General .....................................................................................................................29

Display Messages .....................................................................................................30

Section6 Functional Tests .........................................................................................33

Equipment Required .................................................................................................33

System Tests ............................................................................................................33

Section7 Electronic Tests .......................................................................................... 35

2726-01 Power Supply Board Tests .........................................................................35

Equipment Required ..................................................................................................... 35

Tests ............................................................................................................................. 35

2533-01 CPU - Interface Board Tests .......................................................................36

Equipment Required ..................................................................................................... 36

Tests ............................................................................................................................. 36

2534-01 Front End Board Tests ................................................................................38

Equipment Required ..................................................................................................... 38

Tests ............................................................................................................................. 38

Safety Tests ..............................................................................................................41

Section8 Specifications ............................................................................................. 43

Monitor Model 860 .................................................................................................... 43

Sensors ..................................................................................................................... 44

Gas Calibrator Model 868 .........................................................................................44

Section9 Accessories ................................................................................................ 45

Section10 Parts ............................................................................................................. 47

Model 860 .................................................................................................................47

Model 868 Calibrator .................................................................................................54

Newer Calibrator ........................................................................................................... 54

Older Calibrator .............................................................................................................55

Model 860 Service Manual Rev. 00

1 Safety

1.1 Patient Safety

• The location of the sensor on the patient should be changed periodically to minimize the risk of burns
due to heating of the skin by the sensor. The risk of such a burn is dependent upon the sensor
temperature, duration of application and physiological parameters including local perfusion, body
temperature, and skin thickness.

• TCO

• In areas where electromagnetic devices (i.e., electrocautery) are used, patient monitoring may be

• The PtcCO

• Components of this product and its accessories which have patient contact are latex free.

• Connect only Novametrix supplied transcutaneous sensors and gas calibrators to the TCO

M monitor has electrically isolated inputs. Patient leakage current flowing from the instrument

2

to ground is limited to less than 10
V rms at 60 Hz. For maximum patient and operator safety, the following procedures are
recommended;

• Keep the TCO

• Do not operate the TCO

• Do not touch the patient while making adjustments on the TCO

• Whenever possible, the TCO

equipment in use on the same patient. Outlets that are on the same circuit can be identified by your
hospital’s engineering department.

interrupted due to electromagnetic interference.

value is corrected only during patient monitoring—not during calibration. Refer to the User’s
Manual for more information.

860 monitor front panel input connectors. Refer to “Accessories” on page 45 for listings and catalog
numbers.

µA at 120 V, 60 Hz. Patient isolation is greater than 10 MΩ, 2500

M and its accessories clean.

2

M when it is wet due to spills or condensation.

2

M monitor.

2

M monitor should be connected to the same circuit as other

2

display reading (CO2) is factory set to reflect the metabolic factor for pCO2 and the

2

M Model

2

1.2 Contraindications

• In patients who are hemodynamically compromised, transcutaneous gas values may no longer
reflect arterial gas values due to changes in blood flow to the tissue.

• Patients with extremely sensitive skin should be carefully evaluated prior to monitoring as sensor
heat or adhesive ring application may cause skin irritation. Skin irritation due to the adhesive ring
can be minimized by loosening the adhesive with alcohol or water prior to its removal from the
patient.

• HALOTHANE INTERFERENCE. Halothane is the only known anesthetic gas affecting the
reliability of transcutaneous oxygen (PtcO
Transcutaneous Combination O
oxygen measurements in-vivo has not been determined. Halothane does not affect the
transcutaneous carbon dioxide (PtcCO
Sensor. No known anesthetic gasses affect the performance of the Transcutaneous Oxygen Sensor
(PN:6754) or the Transcutaneous Carbon Dioxide Sensor (PN:6752).

Rev. 00 Model 860 Service Manual 1

/CO2 Sensor (PN:4474). The affect of halothane on transcutaneous

2

) measurement as demonstrated in in-vitro testing of the

2

) measurement of the Transcutaneous Combination O2/CO2

2

1 Safety Contraindications

• PtcO2 levels in excess of 150 mmHg may cause drift of PtcCO2 portion of the 4474-00 Combination
/CO2 Sensor using an 8900 Split Membrane NOVADISK. This drift is not experienced with the

O

2

4474-39 Combination O
Sensor (PN:6754) or the Transcutaneous Carbon Dioxide Sensor (PN:6752).

Indicates a potentially harmful condition that can lead to personal injury.

/CO2 Sensor and 8575 NOVADISK, nor with the Transcutaneous Oxygen

2

WARNING

• Explosion Hazard: Do NOT use the TCO

instrument in such an environment may present an explosion hazard.

• Electrical Shock Hazard: Always turn the monitor off before cleaning it. Do NOT use a damaged

sensor or one with exposed electrical contacts.

• Failure of Operation: If the monitor fails to respond as described, do not use it until the situation

has been corrected by qualified personnel.

• Fire Hazard: The TCO

elevated pressures. Use of this instrument in such an environment may present a fire hazard.

• For installation where the integrity of the external protective earth conductor arrangement is in

doubt, the equipment should be operated from its internal battery only.

• No user serviceable parts inside. Refer servicing to qualified service personnel.

M and its sensors should not be exposed to elevated oxygen levels at

2

M in the presence of flammable anesthetics. Use of this

2

CAUTION

Indicates a condition that may lead to equipment damage or malfunction.

• Federal (U.S.A.) law restricts this device to sale, distribution, or use by or on the order of a licensed

medical practitioner.

• No tension should be applied to the sensor cable.

• Avoid storing the monitor and sensors at temperatures less than -10

F or >131

• Do NOT immerse the monitor or sensors in liquids.

• Do NOT sterilize the monitor or the sensors.

• Electric Shock Hazard. Do NOT remove covers or panels. Refer servicing to qualified service

personnel.

• Connect the line cord only to a grounded hospital-grade outlet.

• For continued protection against fire hazard, replace fuses only with those of the same type and

rating.

• No user serviceable parts inside. Refer servicing to qualified service personnel.

• Operate at temperature between +10° C to +40° C (50-104° F), < 90% relative humidity (non-

condensing).

° F).

° C or greater than +55° C (<14°

2 Model 860 Service Manual Rev. 00

2 Description

0.03 pCO

2

This manual is written for users of the Novametrix TCO2M Transcutaneous monitor, Model 860. The

M is a dual parameter, noninvasive transcutaneous gas monitor. It provides reliable, continuous

TCO

2

measurement, displays and alerts for transcutaneous oxygen tension (PtcO
dioxide tension (PtcCO

Transcutaneous oxygen is measured with an oxygen sensor consisting of two parts; 1) a modified Clark­type polarographic sensor, a silver anode, electrolyte and an oxygen permeable membrane, and 2) a
heating section with two precision thermistors for measuring and controlling the sensor temperature.
When the sensor is subjected to oxygen, the oxygen molecules diffuse through the membrane and create
an electro-chemical reaction which causes current to flow through the cathode. An amplifier connected
to the cathode measures the amount of current flowing and converts it to a value proportional to the
oxygen tension at the sensor/membrane interface. This information is displayed as PtcO

Transcutaneous carbon dioxide is measured with a sensor that utilizes a unique pH sensor based on the
Stow-Severinghaus principle. The carbon dioxide sensor is composed of two parts; 1) a carbon dioxide
sensor consisting of a pH sensor, reference sensor, electrolyte and a carbon dioxide permeable
membrane, and 2) a heating section with two precision thermistors for measuring and controlling the
sensor temperature. When the sensor is subjected to carbon dioxide, the carbon dioxide molecules diffuse
through the membrane and react with the electrolyte. This reaction alters the pH of the electrolyte
solution, which in turn changes the voltage across the pH and reference sensors. Since carbon dioxide is
the only gas that can affect the pH of the electrolyte, there is a direct correlation between pH and the
amount of CO

present. This relationship is expressed by the Henderson-Hasselbach equation:

2

) and sensor temperature.

2

), transcutaneous carbon

2

.

2

HCO

pH = pKa + log

An amplifier measures this voltage change and converts it to a value corresponding to the carbon dioxide
tension at the sensor/membrane interface. This information is displayed as PtcCO

The following sensors may be used with the TCO

Cat. No. Sensor Type

4474-00 Combination O
4474-39 Combination O
6752 Carbon Dioxide Sensor

6754 Oxygen Sensor

Rev. 00 Model 860 Service Manual 3

M:

2

3

/CO2 Sensor

2

/CO2 Sensor

2

.

2

2 Description Conventions

Menu (soft key identifiers)

2.1 Conventions

The following conventions will be used throughout this manual:

• Normal text will be shown in this type.

• Message center displays, menu titles and displays will be shown IN THIS TYPE.

• The names of soft keys will be shown IN THIS TYPE.

• The image of front panel keys (hard keys) will be displayed as their icon,

e.g. - POWER key.

2.2 Summary of Operation

The front panel of the TCO2M contains hard keys (dedicated front panel keys), soft keys (menu
dependent keys) and icon symbols (illuminating indicators). When the monitor is powered up and passes
its self-test, it will display a screen similar to the one below:

CO

Factor

2

PtcCO2 Parameter Information

(upper/lower limits)

Real Time Waveform Display

Trend Parameter & Display Time

Alert Limits

Sensor Temperature

Battery Icon

The display is arranged in different sections; parameter information for PtcCO
waveform display and the menu display. A full screen trend display is also available.

The first menu to appear in normal operation is the main menu, from here all other sub-menus are
accessed by pressing particular soft keys.

and PtcO2, real time

2

4 Model 860 Service Manual Rev. 00

Front and Rear Illustrations Description 2

2.3 Front and Rear Illustrations

Display

TCO2M Calibrator, Model 868 connection

Power button - Press to turn the
monitor on/off.

-used on some models.

“LOW BAT” - Red when
battery is near depletion. (A
similiar icon appears in the dis­play when the monitor is run­ning on battery power and gives
a visual
indication of the charge left on
the battery.)

Red Alert Bar

Sensor input

Audio disable icon - Flashes
yellow when the audio has been
disabled.

Alert Reset key - Press to
acknowledge and reset alerts.

AC indicator - Green when the
monitor is connected to AC

Alert indicator - Flashes red to

indicate an alert condition.
power and the rear panel power
entry module switch is set to “|”
(ON). Also indicates the bat­tery is charging.

Two minute silence indicator ­Illuminates yellow when the
audio has been temporarily

Event key - Press to mark an

event in trend memory.

Contrast key - Press and hold to

vary the contrast of the

display.
silenced using the two minute
silence feature.

Audio key - Press to toggle two
minute silence. Press and hold
for audio disable.

Soft key - Five keys that

function according to the

command shown above each

key in the display.

Rev. 00 Model 860 Service Manual 5

2 Description Symbols

1 2 3

5

4

1 Ground stud. Use to connect monitor’s chassis to earth ground.
2 Indicates fuse rating information for mains fuse.
3 RS232 port for Novametrix accessories.
4 Power cord receptacle and power cord retaining clip. Plug power cord into this

receptacle. Use only hospital grade three wire plugs for connection via supplied
power cord.

6

2.4 Symbols

5 AC Line Power (Mains) Switch. Set to “|” allows AC Mains to power the monitor,

set to “O” switches AC mains power off.

6 Voltage select/fuse compartment - Sets the mains operating voltage and houses

mains fuses.

NOTE: The AC power line cord shipped with monitors for North America is a hospital grade,
SJT style cord with a 120 VAC plug. All power line cords shipped with monitors for Europe
are the european style with a 220-240 VAC plug. All other style power line cords, as
required by the country of destination, are provided by the distributor of that country.

Equipotentiality - Connection to monitor’s chassis.

Patient Isolation - Identifies patient isolation connection as type BF.

Protective earth ground connection

High voltages present

Attention - Consult manual for detailed information.

Mains Fuse - Mains fuse rating for replacement fuses

250V

Mains Power - AC mains switch “|” ON-connection to mains; “O” OFF-disconnection from mains.

6 Model 860 Service Manual Rev. 00

3 Theory of Operation

indicator

3.1 2726 Power Supply Board

The Power Supply Board contains the circuitry needed to charge the battery and to convert the necessary
DC voltage from the AC line. Refer to the “POWER SUPPLY” schematic 2726-03 (location).

3.1.1

AC Mains and Battery Operation Overview

The TCO2M is powered by an internal 12 volt battery that is automatically charged when the monitor is
powered from the AC line. The green icon on the front panel illuminates when the line cord is
connected and the rear panel power switch must be in the “|” (ON) position. This indicates that AC line
power is charging the battery.

A fully charged battery will power the monitor for over three hours. While on battery power, the display
screen shows a battery icon that “drains” as the battery charge is depleted; from a full charge , to half­charge , to nearly depleted . The monitor may not power up on battery power if the battery is not
sufficiently charged.

Low battery

As the battery voltage runs low (
At this point, the AC line should be reconnected to charge the battery.

≈11.5 volts), the (battery indicator) on the front panel will turn red.

Icon appears only when on battery power

If the monitor continues to be powered from a battery in a low voltage situation, at approximately 10.5
volts, a continuous alarm sounds for sixty seconds while the battery indicator will flash red. A
“BATTERY VERY LOW PLUG IN AC POWER” message will appear. If this alarm is ignored, the
monitor will shut down. The AC line should be connected to the monitor to recharge the battery before
this occurs.

3.1.2

Rev. 00 Model 860 Service Manual 7

AC Operation

Reference the Overall Wiring Diagram (see 6590-09). The AC line voltage enters the monitor at the rear
panel Power Entry Module (PM301). This device contains a built in RFI power line filter, a double-pole
single-throw switch that opens and closes both AC input lines, fuses and an input voltage selection key.

3 Theory of Operation 2533 CPU Interface Board

The filtered, switched and fused output of the Power Entry Module is fed to the primary coils of the
system transformer, T301. Reference the Power Supply schematic 2726-03. The secondary output from
T301 is rectified by D1 (bridge rectifier) and filtered by C1. The (loaded) DC voltage at this point is
approximately 20 volts.

The 20 volts DC is fed to the battery charging regulator IC1 (pin 5) through Q1. Biasing for Q1 is
accomplished by D2, R1, and R2 when AC power is applied. When running on battery power, Q1 is
biased off by R1, R2, and D3. This prevents the battery from trying to power the battery charger regulator.
Power to IC2 is also removed, this informs the monitor of the loss of AC via the LINEST line

The output of switching regulator IC1 pin4 is rectified and filtered by D4, C4, and L1, then fed to the
battery through current sense resistor R3 and fuse F302, to J302 pin 1 (VBAT+). The battery float charge
voltage is maintained at 13.2 volts except for fast charge that is regulated at 14.4 volts. The output is also
monitored for over current conditions. These parameters are controlled by IC3 and associated circuitry.
When the battery charge current exceeds a preset limit, IC3 pin 7 goes high which biases Q2 on, this in
turn shorts out R12 which affects the feedback control (FB) to IC1 (pin 1). With R12 shorted out, the
control resistors R14 and R13 set the output voltage to 14.4 volts. When the charge current lowers, IC3
pin 7 goes low which biases Q2 off, this puts R12 back into the feedback control which now consists of
R12, R13 and R14; setting the voltage to 13.2 volts. When more than the maximum charge current flows
through R3, IC3 pin 1 shorts IC1 pin 2 to ground, that shuts IC1 off until its next switching cycle. When
the current reaches a safe level IC3 pin 1 allows IC1 to remain on.

The voltage switched by Q1 is also fed to IC2 as VCH (Voltage Charge). The output of this 5 volt
regulator provides the LINEST (Line Status) signal to the main board. With AC applied, LINEST is high.
LINEST goes low when the AC is disconnected.

3.2 2533 CPU Interface Board

The following sections detail the operation of the CPU Interface board. Refer to the “CPU INTERFACE”
board schematic (2533-03).

3.2.1

Power On/Off Control Circuitry

See page 3 on schematic. The TCO2M power on/off control circuitry consists of the VBACK supply
(regulated by IC12), IC10, IC11 and the front panel power key.

When the battery or AC power is first applied to the power supply board (via VIN J102 pin 1), VBACK
goes to +5 volts. This provides power to IC10 and IC11, and through the C26 and RP4 (pins 3,4) network
at IC10 pin 8, sets IC10 pin 2 to a logic low.

The ON/OFF line is brought low each time the front panel power key is pressed. This sends the output at
IC11 pin 10 high. This low-to-high transition clocks the (#1) D flip-flop portion of IC10. The output at
IC10 pin 2 goes high and with each successive press of the power key, this output toggles to the opposite
level (low or high). A high turns the TCO

While the output at IC10 pin 2 is high, the MOSFET Q7 is turned on and pulls the gate of MOSFET Q8
to ground, thus causing Q8 to conduct as well. With Q8 conducting, the currently active monitor power
source—either the AC power derived supply or the battery supply will flow through Q8 to the voltage
input (pin 7) of the Pulse Width Modulator IC9. The output IC9 pin 6 will oscillate (at the frequency set
by R13 and C15). This causes Q5 to switch on and off and provide a path to ground through the primary
coils of T1 for the supply (line or battery) at T1 pins 9 & 10. Current flowing in the primary is measured
at IC9 pin 3 and the duty cycle of the pin 6 output will vary with the load on the transformer.

M on and a low shuts it off.

2

Current flow in the transformer primary induces current in the three secondary coils and creates the
volt analog supplies, the VRAWI that powers the isolated RS232 circuitry, and the +5 volt VCC supply
that power the remaining circuits in the monitor. The +V5 and -V5 supplies are rectified and filtered by

± V5

8 Model 860 Service Manual Rev. 00

2533 CPU Interface Board Theory of Operation 3

D4, D10, C10, C12, C68 and C69. The +V5 is regulated by IC7 and the -V5 by IC8. The VCC supply is
rectified by D3, filtered by L1, C9 and C20 and fused at F1, and in addition, a feedback loop to IC9
contains VR1 which is factory adjusted to produce a +5.00 volt
load).

± 0.05 volt VCC supply (measured under

3.2.2

3.2.3

Power Supplies

See page 3 on schematic. The secondary winding consisting of pins 1 and 2 are rectified and filtered by
D1 and C1. The rectified voltage at this point is approximately 7 volts DC and is regulated to 5 volts by
IC2. This isolated supply powers the isolated portion of the opto-isolators and the RS232 driver chip IC1.
The unregulated voltage VRAWI is sent to the rear panel connector J101.

The backup voltage (VBACK) is regulated by IC12 from the VIN supply. Capacitors C22 and C27 serve
as filters and D17 allows VCC to power VBACK circuitry when the monitor is on. At this point D18 is
biased off so IC12 is idle. When the monitor is turned off and VCC collapses D18 is then forward biased
and IC12 now supplies VBACK circuitry, D17 at this time is reverse biased and prevents power from
reaching VCC.

Precision Reference Supplies

See page 4 on schematic. The circuitry of the Front End Board requires precise voltage supplies as
references for the A/D convertor and operational amplifier circuitry. The precision references are
generated by IC19B, Q6, and D16 for the +Vref (+2.048 v) supply, and by IC19A, Q4, and D12 for the

-Vref (-2.048 v) supply.
Both of the precision references utilize the same method of placing the regulating diode in the feedback

network of an operational amplifier. For clarity, only the positive reference will be discussed. The
ICL8069, D16, is the temperature compensated 1.22 volt reference used in the feedback loop of the op­amp. The ICL8069 is a temperature compensated, but not current compensated device. The gain of the
op-amp circuitry is approximately 1.7 times that of the ICL8069 voltage. This gain is set by resistors R85
and RP5-2, and potentiometer VR7. The point at which VR7 is tapped sets the gain, since it is connected
to the inverting input of IC19B. The voltage from TP4 and that of the non-inverting input equals that of
the zener voltage of D16. Capacitor C72 acts as a bypass and integrator to any noise across D16.
Transistor Q6 is used as a current boost and low impedance source for the +2.048 volt output at TP4.

Both voltage references have their ICL8069’s tied to the reference output of opposite polarity as a means
of stabilization, tracking, and bias. By placing the zener in the feedback loop of the op-amp, the output
is held at a constant voltage (Vz) times the gain of the circuit. This voltage will remain constant despite
varying current draw.

3.2.4

Rev. 00 Model 860 Service Manual 9

Low Battery Voltage Shutdown

See page 3 on schematic. The CPU monitors the battery voltage and provides the user with a low battery
indicator (), messages and alarms. However, if these are ignored, a hardware circuit will take over and
shut off the monitor before the battery is damaged.

The pulse width modulator IC9 requires at least 7.6 volts at pin 7, its voltage supply, in order to operate.
This pin typically draws 10 mA of current. The resistance of the R63 and Q8 combination is
approximately 114 ohms. This equates to a voltage drop of approximately 1.14 volts. Therefore if the
battery voltage drops under 9.0 volts (approximately), IC9 will not have sufficient voltage to operate and
will shut down. Shutdown of IC9 stops current flow through transformer T1 and the secondary supplies
shut down, effectively turning off the monitor.

When IC9 shuts down, its VREF output at pin 8 is pulled low. This forward biases D6 and causes the
NAND gate output at IC11 pin4 to go high. The #2 flip-flop of IC10 is clocked, and the high at the D2
input (because /Q1

is High) is transferred to the Q2 output at pin 13. The high at pin 13 Sets the #1 flip-

3 Theory of Operation 2533 CPU Interface Board

flop causing the /Q1 pin 2 output to go low. This low shuts off both MOSFETs Q7 and Q8, thereby
blocking any supply voltage from IC9 pin 7. Normally, pressing the front panel power key would clock
flip-flop #1 (at pin 3) and return the pin 2 output high—but the high output at pin 13 keeps the #1 flip­flop Set—and the power key has no effect.

If at this point the AC line is reconnected, MOSFET Q8 continues to block current from IC9 pin 7 and
the monitor remains off. Connecting the AC line does however send the LINEST signal high. This line
is brought to IC10 pin10 where it resets the #2 flip-flop, sending IC10 pin 13 Low and removing the set
condition from flip-flop #1. Now, if the front panel power key is pressed, flip-flop #1 is clocked, IC11
pin11 goes high, MOSFETs Q7 and Q8 turn on, the supply to IC9 pin 7 is restored, the pulse width
modulator restarts, energizes T1, and the monitor turns back on.

3.2.5

3.2.6

Microprocessor

See page 1 on schematic. A Hitachi HD64180RP microprocessor directs the actions of the TCO2M. The
processor, IC16, is operated at 6.144 MHz (half the12.288 MHz frequency of crystal Y1), has an 8-bit
data bus and a 19-bit address bus (the 860 uses only 18-bits). The microprocessor also provides two
asynchronous serial communication channels, a clocked serial I/O port and various interrupt and control
signals. The +5 volt VCC supply to the processor is first sent through inductor FB1, a ferrite bead, before
powering the chip at IC16 pin 32.

Memory

The TCO2M system software is located at IC17, a 27C010 EPROM. The 128 K byte RAM, IC20, stores
trend data, system power up settings (calibration parameters, serial output parameters, etc.), and provides
an area for system memory requirements. Since IC20 is powered from the VBACK supply, RAM
memory is retained when the monitor is turned off and it becomes available again when the monitor is
turned back on.

The ROM at IC17 is read when its Chip Enable line (IC17 pin 22) is brought low by the ROMCS
at IC25 pin 3, and the processor brings its Read line (IC16 pin 63) low—thereby activating the ROM
Output Enable line at IC17 pin 24. Under these conditions, ROM data from the specified address bus
location is made available to the data bus for use by the processor.

The RAM (IC20) is activated when its Chip Select line RAMCS* (IC20 pin 20) is brought low, via IC25
pin 8. When the ME* line at IC25 pin 5 is low, and the inverse of address line A17 at IC25 pin 4 is low,
output pin 6 of IC25 will go low. This in turn will drive IC25 pin 10 low, with PWRON* low at IC25 pin
9, IC25 pin 8 will be low (RAMCS*). If at that time, OE
whereas a RAM Write will occur if WE

(IC20 pin 27) is low.

(IC20 pin 22) is low, a RAM Read occurs,

signal

3.2.7

Real Time Clock (RTC)

See page 2 on schematic. A Real Time Clock (IC24) provides the TCO2M the ability to time stamp
collected (printed) trend data. The 32.768 kHz crystal, Y3, provides the timing signals for the clock chip,
IC24, which is powered from the VBACK supply so that the clock can continue to keep time when the
monitor is turned off (provided the monitor’s 12 volt internal battery is connected and maintains at least
a nominal charge).

The RTC is activated when its Chip Select line (CS0) at IC24 pin 2 is brought low. With the monitor on
PWRON will be low (IC25 pin 13, see page 1 on schematic), the RTC line will be brought low by the
processor through IC22 pin 14, these lines drive RTCCS (Real Time Clock Chip Select IC25 pin 11) low.
If at this time, the RD
the WR
D3 (pins 14-11).

(IC24 pin 10) input is low. Addressing is handled by A0-A3 (pins 4-7) and data I/O through D0-

(IC24 pin 8) input is low, a RTC Read occurs, whereas a RTC Write will occur if

10 Model 860 Service Manual Rev. 00

2533 CPU Interface Board Theory of Operation 3

3.2.8 Sound generator

See page 2 on schematic. A programmable tone generator, IC27, is used to drive the monitor’s audio
circuit. The tone generator is clocked by IC4 pin 9 (Q1). The tone generator is enabled by the processor
when IC22 pin12 is brought low. While CE
frequency (pitch) and attenuation (volume) is accepted by the tone generator. The Ready signal (IC27 pin

4) goes low while accepting data and the processor is put into a Wait state until IC27 finishes its task;
then Ready returns high and the processor continues its operations.

The AUDOUT output at IC27 pin 7 drives the audio amplifier IC26. The amplifier output is coupled
through capacitors C55 and brought to J109 as the SNDOUT (Sound Out) line. The speaker which is
mounted in the chassis is connected to J109.

is low, WR is brought low and data bus information including

3.2.9

3.2.10

Keypanel Interface

See page 2 on schematic. The 10 keys on the TCO2M front panel are connected through a ribbon cable
at J104. Each key (except power) is connected to an 8-bit latch (either IC14 or IC15). When any of these
keys are pressed, the corresponding latch input is brought low. The processor continually reads the status
of these latch outputs, the RDKEY enables IC14 when low and the RDKEY_2 line enables IC15 when
brought low.

The power key ON/OFF signal is sent through J104 pin 15. The AC Line Status signal, LINEST, is
generated by the power supply, and is high (+5 volts) when the monitor is connected to the AC line and
the rear panel switch is set to “|”. This +5 volt level is sent to the green indicator on the keypanel via
J104 pin 16. The LINEST signal is also input to the latch at IC14 pin 8 so that the CPU can detect if the
unit is operating on AC line power (IC14 pin 8 high) or on battery power (IC14 pin 8 low). Diode D9
keeps current from back feeding into IC14 when the monitor is turned off but still connected to the AC
line.

The TML (Two Minute Lamp), AOL (Audio Off Lamp), ARL (Alert Reset Lamp), and BTL (Battery
Lamp) LEDs are driven by the 8-bit latch IC13. When each of the corresponding signals is driven high
the appropriate LED on the keypanel is illuminated.

Display Interface

See page 1 on schematic. The display is connected at J107 (see page 1 on schematic). It is controlled by
the processor using the RD (Read), WR (Write), and DISPCS (Display Chip Select) lines. Data bits D0­D7 are used as input/output lines and A0 is used in conjunction with the RD and WR lines to distinguish
between read and write operations as listed below.

A0 RD Low WR Low

High Status Read

Low Data Read Data Write

See page 2 on schematic. The CNTRST (Contrast) line is controlled by pressing the front panel key.
When depressed and held the processor controls the digital to analog converter IC29, line A0 is brought
low along with WR and DACCS, the data on D0-D7 controls the voltage at IC30 pin 7. The output of
IC30 pin 7, along with +V5 feeds a summing amplifier (IC30 pins 1, 2, 3). The output of the summing
amplifier IC30 pin 1 controls the base of Q10 which in turn controls the contrast of the display through
a variable negative voltage.

The backlight for the display is controlled by the DISPBR (Display Bright) line (see page 2 on
schematic). When DSPBR is high the gate of Q16 is biased off, current flows from Vcc through R51 to
IC45. This sets the backlight for low illumination. The illumination of the backlight is made greater when

Rev. 00 Model 860 Service Manual 11

Command

Write

3 Theory of Operation 2533 CPU Interface Board

DSPBR is made low, this biases Q16 on which essentially shorts out R51 allowing more current to flow
into IC45 creating a full backlight.

3.2.11

I/O Device Controller

See page 1 on schematic. The ADC_CS, ZPRESS, HEATER, HYP, INTACK, FLWREN, SCK, and DIN
lines are all controlled by IC28 when selected by the OPORT line (IC21E pin 10). The OPORT line will
go high when the LATCH1 and WR line both go low at IC23D pins 13 and 12, this will send output pin
IC23D pin 11 low which drives inverter IC21E pin 10 high enabling IC28.

ADC_CS: Analog to Digital Converter chip select
ZPRESS: Zero barometric pressure line
HEATER: Heater enable/disable
HYP: Hyperbaric mode line
INTACK: Interrupt acknowledge line
FLWREN: Flash write enable line
SCK: Serial clock line for the A/D converter
DIN: Data in line for the A/D converter

A 3 to 8 decoder is used to control the DACCS, RTC, DISPCS, AUD, KEYS, LATCH1, LATCH2,
2KEYS lines. When the IOE line goes low and the LIR line goes high being inverted by IC21A pin 2 and
presented to IC22 pin 5 as a low enable line IC22 is enabled, Y0-Y7 will be driven low depending upon
the A4, A5 and A6 lines on pins 1, 2, 3 respectively on IC22.

See page 2 on schematic. With the LPORT line high IC13 is enabled, this latches the data on lines D0­D7 on its output pins Q0-Q7, the outputs correspond to the following eight lines:
CALLOW-selects the low calibration gas on the Model 868 Calibrator
TML-Two Minute LED drives the LED on the front display.
AOL-Audio Out LED drives the LED on the front panel.
ARL-Alert LED drives the LED on the front panel.
KJL-drives Q17 when high which in turn drives the Alert Bar LEDs via J105.
BTL-Battery Low LED on the front panel.
DSPBR-controls the display backlight via Q16 and IC45
CALHIGH-selects the high calibration gas on the Model 868 Calibrator

3.2.12

3.2.13

Watchdog Timer

See page 1 on schematic. The Watchdog Timer provides a system reset function in the event a hardware
or software “glitch” occurs.

At power up and at specific intervals thereafter, the microprocessor outputs a logic high to IC5 pin 6,
WDOG (Watchdog). If the WDOG pulse does not appear at regular intervals, as the result of a software
or hardware problem, the RC charges up and IC21 pin 8 goes low producing a low at IC16 pin 7 (CPU
RESET line). The output at IC21D drives the RESET line of IC4. The Q14 output of IC4 will drive the
output of IC3B, which in turn drives IC3A pin 5 a CPUINT (CPU interrupt) line. This will cause the
processor to reset. The monitor then performs its power up self-test routines, and if the “glitch” has been
cleared, the monitor resumes normal operation. If the problem still exists, a self-test or other error should
be displayed.

RS232 Serial Communication

See page 3 on schematic. The TCO2M supports serial (RS232) communication with external devices via
the monitor’s rear panel connector. Signals to and from the rear panel RS232 connector are electrically
isolated from the rest of the TCO

M electronics by four opto-isolators (IC6, IC31-IC33).

2

12 Model 860 Service Manual Rev. 00