Welch Allyn SureTemp 986 User manual

Service Manual
SureTemp®
Model 986 Thermometer
Welch Allyn, Inc.
7420 Carroll Road
San Diego, CA 92121
Thermo Menu
Operator Manual

70995-0000B Technical Manual M986 © 2001
© 2000, 2001 by Welch Allyn, Inc. All rights reserved. No part of this manual may be
reproduced or transmitted in any form or by any means, electronic or mechanical, including
photocopy, without prior consent in writing from Welch Allyn, Inc. Printed in the USA
Welch Allyn andSureTemp are trademarks of Welch Allyn, Inc. All rights reserved.

Model 986 Thermometer i
Contents
1. General Information......................................................................................................1
1.1 About the Model 986.................................................................................................1
1.1.1 System Block Diagram...................................................................................1
1.2 Technical Support.....................................................................................................1
1.3 Safety Warnings and Notices ....................................................................................2
1.4 Classifications..........................................................................................................2
1.5 About this Manual ....................................................................................................3
1.5.1 Related Documents........................................................................................3
1.6 Return Procedure .....................................................................................................3
1.7 Terms used in this Manual ........................................................................................4
2. Service ..........................................................................................................................5
2.1 Basic Operation of the Model 986 ..............................................................................5
2.1.1 Types of units................................................................................................5
2.1.2 Major Thermometer Components.....................................................................6
2.1.3 Instrument Reset ...........................................................................................6
2.1.4 POST (Power Up Self-Test).............................................................................7
2.1.5 Probe Type Test ............................................................................................7
2.1.6 Operational Checks........................................................................................8
2.1.7 Default algorithm for oral and axillary modes (blue probe)................................11
2.2 Service Procedures.................................................................................................11
2.2.1 List of Tools and Equipment..........................................................................11
2.2.2 Preventative maintenance.............................................................................12
2.2.3 Cleaning and Sterilization .............................................................................13
2.2.4 Service Activities..........................................................................................14
2.2.5 Component Replacement..............................................................................14
2.3 Battery Removal and Replacement...........................................................................15
2.3.1 Battery Life..................................................................................................15
2.4 Calibration Procedures............................................................................................16
2.4.1 Calibration Limits Table ................................................................................16
2.4.2 Water Bath procedure ..................................................................................16
2.4.3 Variable Temperature Water Bath procedure...................................................16
2.4.4 Model 9600 Calibration procedure..................................................................17
3. Troubleshooting ..........................................................................................................19
3.1 Error Codes ...........................................................................................................19
3.1.1 Types of Errors ............................................................................................20
3.1.2 Error Recall Mode........................................................................................21
3.2 Troubleshooting Table.............................................................................................22
3.3 Disassembly/Reassembly.......................................................................................24
3.4 Field Serviceable Parts ...........................................................................................24
3.4.1 Main Components........................................................................................24
3.4.2 Model 986 PCA ...........................................................................................26

ii 70995-0000B M986
3.4.3 Replacement Parts for PCA ..........................................................................27
Appendix A. Theory of Operation.....................................................................................29
A.1 Overview................................................................................................................29
A.1.1 Temperature Probes.....................................................................................30
A.1.2 Probe Switch...............................................................................................30
A.1.3 Normal Mode Description..............................................................................30
A.1.4 Power Supply..............................................................................................31
A.1.5 Microcontroller.............................................................................................31
A.1.6 Reset/Self Tests..........................................................................................31
A.1.7 Microprocessor Clock...................................................................................32
A.1.8 Temperature Measurement And Display.........................................................32
A.2 Temperature Measurement A/D Converter.................................................................32
A.2.1 Use of Analog Circuitry.................................................................................32
A.2.2 A/D Theory of Operation ...............................................................................32
A.2.3 Circuit Description........................................................................................33
A.2.4 Probe Type Detection...................................................................................34
A.2.5 Instrument ID Logic......................................................................................34
A.2.6 Circuit Operation..........................................................................................34
A.3 Probe warming (Oral probes only)............................................................................35
A.3.1 Theory of Operation......................................................................................35
A.3.2 Circuit Operation..........................................................................................35
A.3.3 Liquid Crystal Display...................................................................................36
A.3.4 Probe Switch...............................................................................................36
A.3.5 Mode Button................................................................................................36
A.3.6 Horn ...........................................................................................................37
Appendix B. Specifications..............................................................................................39
Appendix C. Limited Warranty.........................................................................................41
Appendix D. Wiring Diagram ...........................................................................................43

Model 986 Thermometer iii
List of Figures
Figure 1: System Block Diagram ..............................................................................................1
Figure 2: Model 986 Thermometer.............................................................................................5
Figure 3: M986 Display ............................................................................................................7
Figure 4: Peak Monitor Mode....................................................................................................9
Figure 5: Battery Removal and Replacement............................................................................15
Figure 6: Thermometer Assembly ...........................................................................................24
Figure 7: Printed Circuit Assembly..........................................................................................26
Figure 8: System Block Diagram ............................................................................................29
Figure 9: Schematic Diagram .................................................................................................43
List of Tables
Table 1: Self-Test Error Table..................................................................................................20
Table 2: Main Components.....................................................................................................25
Table 3: Replacement Parts for PCA .......................................................................................27
Table 4: Configuration Truth Table ...........................................................................................34

iv 70995-0000B M986

Model 986 Thermometer 1
1. General Information
1.1 About the Model 986
The Welch Allyn Model 986 SureTemp is a portable, predictive
thermometer that accurately measures body temperatures in a
few seconds at oral, axillary, or rectal sites. Oral/axillary and rectal
probes utilize single use disposable probe covers to help limit
cross-contamination.
This instrument was developed for use by medical professionals
and day care providers. The predictive technology allows the user
to take oral temperatures in approximately four seconds, axillary
temperatures in approximately 10 seconds (for children under four
years), and rectal temperatures in approximately 15 seconds.
1.1.1 System Block Diagram
Model 986 PCA
NEC UPD 789407 uP
Probe Assembly
A/D Converter
Circuit
Voltage
Reference Circuit
Battery Detector
Circuit
16 Bit
Timer
8 Bit
A/D
CPU
LCD
Driver
Serial
I/O
Horn
Driver
Serial
Port
Mode
Button
Configuration
Horn
Probe Warmer
Circuit Liquid Crystal Display
Probe
Configuration
Jumpers
Four Conductor
Coil Cord
Thermistor Probe
Warmer
2 AAA
Batteries
Figure 1: System Block Diagram
1.2 Technical Support
Contact Welch Allyn Customer Service at:
Welch Allyn, Inc
7420 Carroll Road
San Diego, CA 92121
800-535-6663

1. General Information
270995-0000B M986
1.3 Safety Warnings and Notices
1. DO NOT USE THIS INSTRUMENT IN THE PRESENCE OF
FLAMMABLE ANESTHETICS.
2. Do not use this instrument for any purpose other than those
specified in the User’s Guide. Doing so will invalidate the
instrument’s warranty.
3. Oral/Axillary SureTemp thermometer models (with a blue
ejection button at the top of the probe) are to be used for taking
oral and axillary temperatures only. Rectal models (red
ejection button) are to be used for taking rectal temperatures
only. Use of a probe at the wrong type of site will result in
temperature errors.
4. Use only single-use Welch Allyn disposable probe covers. The
use of any other probe cover or the failure to use a probe cover
may produce temperature measurement errors and increase
the chances for cross-contamination.
5. The thermometer case is not waterproof. Do not immerse it in
liquids or drip fluids onto it.
6. Dispose of batteries in accordance with all local, state and
federal environmental guidelines.
7. This instrument consists of high quality precision parts and
should be protected from severe impact and shock. Do not use
the thermometer if you notice any signs of damage to the
probe or instrument. Contact Welch Allyn Customer Service at
[phone] for immediate assistance.
Note: This thermometer complies with current required
standards for electromagnetic interference and should
not present a problem to other equipment or be affected
by other devices. As a precaution, avoid using this
device in close proximity to other equipment.
1.4 Classifications
Type of protection against
electric shock Internally Powered Equipment
Degree of protection against
electric shock Type BF Applied Part
Degree of protection against
ingress of liquids Ordinary (IPXO)
Degree of safety in the
presence of flammable
anesthetics
Equipment not suitable for use
with flammable anesthetics
Mode of operation Continuous

1. General Information
Model 986 Thermometer 3
1.5 About this Manual
This manual describes both the Model 986 Oral/Axillary and Rectal
thermometers. Most topics and procedures are equally applicable
to both products. Where there are differences, we will note which
instrument is being discussed.
1.5.1 Related Documents
End user operation of the Model 986 is covered in the M986
User Guide and Quick Reference Guide.
Model 986 User Guide 70994-1000
Model 986 Quick Reference Guide 71019-0000
This Service Manual assumes that the technician understands
these operations.
1.6 Return Procedure
Contact Welch Allyn Customer Service at [phone] before
returning an M986 Thermometer to the factory for service.

1. General Information
470995-0000B M986
1.7 Terms used in this Manual
The following abbreviations are used in this manual:
Main Component Terms
PCB Printed circuit board (the board itself)
PCA Printed circuit assembly (with all components)
LCD Liquid Crystal Display
BATT. Battery.
DMM Digital Multi-Meter
O-Scope Oscilloscope
Component Reference Terms
CCapacitor
DDiode
ETest point
JConnector jack
LInductor
LS1 Horn
PConnector plug
QTransistor
RResistor
SSwitch
UIntegrated circuit
XCrystal, resonator

Model 986 Thermometer 5
2. Service
2.1 Basic Operation of the Model 986
The Model 986 is a portable digital thermometer. Service
technicians should check the basic operation of the instrument
before it is disassembled.
Figure 2: Model 986 Thermometer
2.1.1 Types of units
The M986 is available from the factory in the following
configurations:
•Oral /Axillary or Rectal Probe
•°F/°C, °F Only, °C Only
Note:Thermometer configuration cannot be modified in the field.
1Probe cover ejection button
2Probe cover box
3Probe storage channel
4LCD display
5Mode button
6Battery Compartment

2. Service
670995-0000B M986
2.1.2 Major Thermometer Components
Batteries The Model 986 thermometer uses two standard
disposable alkaline AAA cells. These batteries
provide long life for reduced down time. No battery
charging is required or possible.
Probe Two types of probes are available: Oral/Axillary
(blue), and Rectal (red). The probe isnot detachable
and is connected to the printed circuit board at the
factory.
Probe
Covers The probe covers are unchanged from previous models and are compatible across all of Welch
Allyn’s thermistor-based thermometers.
Note: The use of probe covers other than Welch
Allyn PN 05031 is not allowed, and will affect
the accuracy of the instrument.
2.1.3 Instrument Reset
If a problem is reported with an instrument, please check its
operation before resetting it.
Reset Procedure
1. Remove the batteries from the instrument (see page 15).
2. After battery removal, any remaining charge due to internal
capacitance must be discharged to achieve a proper reset.
After the batteries are removed, press the Mode button for
about five seconds. The electronics will now properly reset
when the batteries are replaced.
3. Reinstall the batteries. Watch the display and observe the
power up self-test (page 7).

2. Service
Model 986 Thermometer 7
2.1.4 POST (Power Up Self-Test)
The self-test includes a series of internal microprocessor self
tests, instrument electronics tests, and the display test. If there are
internal electronics problems detected by the self-tests, the Err
(error) icon will be displayed and an audible tone will sound. Refer
to the Error Codes table in the Troubleshooting section (page 19)
for an explanation of any error code. The M986 electronics are
tested each time the batteries are replaced.
•The Power up test begins with all display segments and icons
simultaneously illuminated, followed by a display of the
software revision in this instrument. The M986 beeper also
briefly sounds at the beginning of the test.
Figure 3: M986 Display
•At the end of the test, the display goes blank and the unit is
ready to operate.
If there is no display, any missing segments, or no beeper, refer to
the Troubleshooting table (page 22).
2.1.5 Probe Type Test
Test the probe to make sure that the correct type of probe is
attached to the unit.
With the probe shaft in the probe well and the display blank, press
the Mode button for three seconds. After three seconds, the
instrument will beep and the display shows the icon with
the measuring site blinking.
•For a blue (oral/axillary) probe, either the head or arm should
blink, depending on whether the instrument is configured for
Oral or Axillary measurements.
•With a red (rectal) probe, the leg icon should blink.
If the wrong icon is blinking, there is a problem with either the probe
or the probe type configuration in the instrument.
1. Refer to the mode table on the schematic diagram (Appendix D).
2. In the mode table, locate the type of instrument – oral only,
rectal only, etc. that you are using.
3. Open the thermometer and locate the jumpers. Verify that the
jumpers are configured for your type of unit.
4. If the jumpers are not configured properly, contact Welch Allyn
Customer service for assistance.

2. Service
870995-0000B M986
2.1.6 Operational Checks
Normal Mode
Normal mode operation is the rapid mode of temperature taking.
This is the default mode and is automatically selected when the
probe is withdrawn from the probe well.
1. When the probe is withdrawn from its storage well, every
segment on the display will be illuminated. Watch for the
display to change from the all segments test to the body icon
display.
2. When the unit is ready, it will beep. The °F or °C symbol
(whichever is selected) will illuminate, and the measuring site
(oral, axillary, rectal) will begin to blink.
3. Load the probe cover at this time. The instrument is now ready
for the probe to be placed in the measuring site.
Note: It is possible that the display will switch from the measuring
site display to the “walking segments” display and back
again several times before the probe is inserted in the site.
This is acceptable operation and will not adversely affect
the temperature taken.
Monitor Mode
The thermometer will automatically switch to Monitor Mode under
certain conditions:
•If the instrument determines that room temperature is above
33.9°C (93.0°F).
•If the thermometer is unable to predict a temperature, after 15
seconds for Oral/Axillary and 30 seconds for rectal, due to
improper technique such as excessive probe movement at any
patient site (i.e. mouth, rectum, axillary).
Note: The thermometer reads the probe temperature immediately
upon removal from the storage well. If the probe was just
replaced from a previous temperature and immediately
extracted, insufficient time may have passed to allow the
probe to cool to room temperature. This will cause the
instrument to determine room temperature to be higher
than actual. The instrument will switch to Monitor mode
immediately if it detects room temperature to be above 33.9
°C (93.0°F). For best results, the user should wait at least
30 seconds between Normal mode temperature
measurements.
If Monitor mode does not display expected temperatures, refer to
the Troubleshooting table on page 22.

2. Service
Model 986 Thermometer 9
Temperature Display
With correct use, the patient’s temperature will be displayed in
about four seconds in oral mode, about 10 seconds in axillary
mode, and about 15 seconds with a rectal probe. The instrument
will beep to signal completion of the Normal Mode temperature
cycle.
Automatic Shutoff
If the probe is left out of the storage well after completion of a
Normal mode temperature, the unit will shut off automatically after
10 seconds to conserve power. Simply replace the probe in the
storage well to prepare for the next temperature.
The instrument will shut off automatically if the probe temperature
remains below 28.9°C (84.0°F) for more than 30 seconds.
Peak Monitor Mode
Peak Monitor mode allows long term monitoring of a patient’s peak
temperature. Unlike predictive mode, Peak Monitor mode will follow
a temperature as it rises and display this temperature until the
probe detects a higher temperature. When this occurs, the higher
temperature is displayed.
Peak Monitor mode provides a direct readout of the peak probe
temperature. The instrument can set in Peak Monitor mode by
immediately pressing the Mode button for two seconds after a
predictive (normal) temperature has been taken.
Figure 4: Peak Monitor Mode
Peak Monitor mode will be indicated on the display by a continuous
temperature reading with a blinking °°For °°CIcon at the upper right
corner of the LCD, and by the body icon disappearing.
Constant
Temperature
Flashing
Body icon disappears

2. Service
10 70995-0000B M986
The typical slow rise in temperature when Peak Monitor mode is
used is due mainly to the mouth temperature slowly recovering
from placement of the colder (room temperature) probe. The probe
itself is actually very fast at rising to the temperature of its
surroundings, usually reaching it within a few seconds. Because of
this slow mouth recovery, three minutes is the recommended time
to wait before recording a Peak Monitor mode temperature.
Peak Monitor mode is also useful in testing the accuracy of the
thermometer when the probe can be warmed to a known
temperature, as with a Welch Allyn Model 9600 Calibration Tester
or in a water bath (see section 2.4).
In Peak Monitor mode, after approximately 60 seconds of no
increasein temperature, the °°C / °°Ficon stops flashing. You will
hear two triple beep sounds, and the peak temperature will be
displayed on the LCD.
Note: If the unit is left in Peak Monitor Mode for a total of five
minutes, it will automatically shut off to conserve power.
If Peak Monitor mode does not display expected temperatures,
refer to the Troubleshooting table on page 22.
°F / °C Conversion
When a final temperature is displayed (in Normal, Recall, or
Monitor mode), press and release the Mode button to toggle the
temperature between °F/°C.
Note: A recalled temperature will be displayed in whichever scale
(°F/°C) is selected at the time of recall. This setting can be
changed during display.
If pressing the Mode button does not change the scale of the
displayed temperature, refer to Mode Button Problems in the
Troubleshooting table on page 22.
Temperature Recall
With the instrument in low-power mode (sleep mode or blank display),
press and release the Mode button to cause the most recent
measured temperature to be displayed for five seconds. The stored
temperature value appears with a °F or °C symbol (whichever is
selected) and an M indicating it is from memory.
•If the recalled temperature was a normal mode temperature,
the flashing symbol of the measurement site is also displayed.
•If the recalled temperature was a Peak Monitor temperature,
only the temperature is displayed, with no site indicated.
Activation of the probe well switch (place the probe in the well) will
interrupt the temperature recall function.

2. Service
Model 986 Thermometer 11
Temperature recall problems
If the last temperature cannot be recalled, refer to Temperature
Recall Problems in the Troubleshooting table on page 22.
If pressing the Mode button does not change the scale of the
displayed temperature, refer to Mode Button problems in the
Troubleshooting table.
2.1.7 Default algorithm for oral and axillary modes
(blue probe)
Two predictive algorithms are available: oral and axillary. To
change the default algorithm:
1. Place the unit in low power mode.
2. Press and hold the Mode button for at least two seconds, until
a short beep is heard. The current algorithm will be displayed.
3. To advance to the next algorithm, press the Mode button
momentarily.
Note:When replacing the batteries, the default power up setting is
the oral predictive algorithm.
2.2 Service Procedures
2.2.1 List of Tools and Equipment
Most service operations can be performed with standard tools and
test meters:
•A #1 Phillips screwdriver can be used for all instrument
screws.
•A standard lab 3.5 digit digital multi-meter (DMM) will provide
sufficient accuracy for most tests. A needle-tipped pair of
probes is recommended. An oscilloscope is sometimes the
only way to analyze high speed signals, but is not generally
required.
•Standard electronics tools and supplies for small surface-
mounted and through-hole component rework will be needed to
perform any electronics repairs. Some surface-mounted
components are extremely small and present a challenge for
rework by hand. A light touch, tweezers, sharp soldering iron
tip, and low heat (#7 tip) are recommended.
•Power (+) and ground (-) are available at the battery terminals.
•Be sure to service the instrument in an ESD-safe work area.

2. Service
12 70995-0000B M986
2.2.2 Preventative maintenance
Units that are used on a regular basis should have the following
preventative maintenance performed at least every six months:
1. Visually inspect the thermometer for physical damage that
might cause future product failure.
2. Clean the unit per the instructions in the User Guide supplied
with the thermometer and/or per the instructions below.
3. Perform the Power on Self Test (page 7), Startup Display Test
(page 7), and the Calibration Test procedure (page 16).
Long Term Storage
Remove the batteries from units that are to be stored for an
extended period and not used.
Regular Tests and Calibration
Perform the following tests every 12 months regardless of storage
and usage levels:
1. Replace the batteries (page 15).
2. Perform the Power on Self Test (page 7), Startup Display Test
(page 7), and the Calibration Test procedure (page 16).

2. Service
Model 986 Thermometer 13
2.2.3 Cleaning and Sterilization
Routine Cleaning
Clean the exterior of the Model 986 and the probe as needed.
•Use a Q-Tip to clean the probe well.
•Wipe all surfaces with a clean cloth dampened with warm
water and a mild detergent, alcohol, or a nonstaining
disinfectant such as Sporicidin

Spray1and Towelettes
cleanser.
Care should be taken not to scratch the LCD faceplate. Make sure
that the cloth is damp, but not too wet.
•Do not allow cleaning solution to flow inside the instrument.
•Never immerse the thermometer into the cleaning solution.
•Never autoclave the thermometer or probe.
Gas Sterilization
When no other form of decontamination such as a germicidal wipe
is acceptable, a low temperature (not to exceed 48.9°C or 120°F)
ETO gas sterilization cycle may be used. Refer to your institution’s
standard operating procedure for the length of the cycle.
Note: Gas sterilization may cause some hazing of glossy plastic
surfaces and should be used only when absolutely necessary.
1. Remove the probe from its storage well and disconnect it from
the instrument.
2. Remove any probe covers from the probe and from the probe
cover storage well.
3. Remove the batteries following the instructions on page 15.
WARNING: Leaving batteries in the thermometer during the
sterilization procedure may present an explosion
hazard.
4. Wrap the thermometer in standard sterilization packaging such
as the Baxter Tower Dualpeel Sterilization Pouch.
5. ETO gas sterilize the instrument at a temperature not to
exceed 48.9°C (120°F) and aerate.
6. Remove the sterilization packaging.
7. Allow the probe and instrument to stabilize to room
temperature for at least one hour before reinstalling the
batteries and probe.
1Sporicidin is a registered trademark of Sporicidin International [phone].

2. Service
14 70995-0000B M986
8. Reinstall the batteries (see page 15) and verify a successful
self-test.
9. Reinstall the probe connector and insert the probe into the
storage well to start the probe initialization process.
10. Verify proper calibration of the thermometer and probe using
the Welch Allyn Model 9600 Calibration Tester.
2.2.4 Service Activities
Field Service Repairs
Repairs are considered field serviceable if the repair will not alter
the calibration or proper operation of the instrument. Recalibration
requires a computer-based system and is normally performed at
the factory.
Factory Repairs
Because of programming requirements, if problems are traced to
microcontroller U1, the unit must be returned to the factory or
properly equipped service center for repair.
2.2.5 Component Replacement
All components in the Model 986 can be replaced without affecting
instrument operation or calibration. Changing R13 will cause some
minor changes to the exact calibration point, but as long as the
proper type and tolerance resistors are used (0.05%, as supplied
by Welch Allyn), the unit will remain within specifications.
LCD Frame Repair or Replacement
Replacement of the LCD frame is somewhat difficult due to the
need to assemble it while under pressure to assure proper
compression of the elastomeric connector.
Note: Do not glue the LCD frame to the display PCB if the frame
pins are broken. This will destroy the display PCB. Replace
the LCD frame with a new LCD frame.