Gaymar MEDI-THERM III User manual

MEDI-THERM®III
HYPER/HYPOTHERMIA MACHINE
MTA6900 SERIES
SERVICE MANUAL
LISTED 303L
P/N 12147-000 1/04
U. S. PATENT NO. 6,517,510
CANADIAN PATENT NO. 2,411,539

SERVICE MANUAL
Medi-Therm®III
Before you begin . . .
CAUTION
Federal law restricts this device to sale by
or on the order of a physician.
WARNING
•Repairs should be performed only by qualified
personnel such as certified biomedical
electronics technicians or certified clinical
engineers familiar with repair practices for
servicing medical devices, and in accordance
with the Medi-Therm®III Service Manual.
•Always perform the FUNCTIONAL CHECK
AND SAFETY INSPECTION (section 7.3, p. 20)
after making repairs and before returning the
Medi-Therm III machine to patient use.
Improper repair may result in death or
serious injury, equipment damage, or
malfunction.
RECEIVING INSPECTION
Upon receipt, unpack the Medi-Therm III machine. Save all
packing material. Perform a visual and mechanical
inspection for concealed damage by removing the
wraparound from the chassis (see page 75). If any damage is
found, notify the carrier at once and ask for a written
inspection. Photograph any damage and prepare a written
record. Failure to do this within 15 days may result in loss
of claim.
Refer to section 7.0 of this Medi-Therm III Service Manual for
additional details.
OPERATING INSTRUCTIONS
For information on operating the Medi-Therm III machine,
refer to the Medi-Therm III Operator's Manual.
Medi-Therm and Clik-Tite are registered trademarks of Gaymar Industries, Inc.
©2000. Gaymar Industries, Inc. All rights reserved. www.gaymar.com
Do not return the Medi-Therm III machine to
Gaymar Industries without first contacting
Gaymar's Technical Service Department for
assistance.
Telephone: Direct [phone]
Toll Free 1 800 828-7341
IMPORTANT
Before operating the Medi-Therm III machine, remove
the compressor shipping braces. See p. 88, figure B.
SAFETY PRECAUTIONS

SERVICE MANUAL
Medi-Therm®III
i
CONTENTS
TABLES
Table Description Page
1 High Temperature Limits .......................................................................... 25
2 RFU Error Codes ......................................................................................... 35
3 Service Modes .............................................................................................. 36
4 Celsius/Fahrenheit Conversion .................................................................. 65
5 Temperature vs. Resistance ....................................................................... 66
6A Operator Controls/Indicators .................................................................... 68
6B Operator Controls/Indicators .................................................................... 71
7 Parts List (base) ........................................................................................... 77
8 Parts List (head) .......................................................................................... 78
9 Control/Display Board Parts List .............................................................. 85
10 Power Supply Board Parts List .................................................................. 86
CONTENTS
Section Description Page
1.0 PATIENT SAFETY ....................................................................................... 1
2.0 MACHINE PRECAUTIONS ....................................................................... 3
3.0 REPAIR POLICY ........................................................................................... 4
3.1 In-Warranty Repairs ............................................................................. 4
3.2 Out-of-Warranty Repairs ..................................................................... 4
4.0 SPECIFICATIONS ....................................................................................... 5
4.1 Physical Specifications .......................................................................... 5
4.2 Thermal Specifications ......................................................................... 5
4.3 Electrical Specifications ........................................................................ 6
5.0 PROBE INFORMATION ............................................................................. 7
6.0 THEORY OF OPERATIONS ...................................................................... 9
6.1 Machine .................................................................................................. 9
6.2 Interconnections ................................................................................... 11
6.3 Power Supply ......................................................................................... 12
6.4 Machine Functions ................................................................................ 12
7.0 FUNCTIONAL CHECK, SAFETY INSPECTION,
PREVENTIVE MAINTENANCE................................................................. 18
7.1 Receiving Inspection ............................................................................. 18
7.2 Cleaning Procedures ............................................................................. 18
7.3 Functional Check and Safety Inspection ............................................ 20
7.4 Inspection Form .................................................................................... 33
8.0 TROUBLESHOOTING & SERVICE MODES ........................................... 34
8.1 Service Modes ........................................................................................ 34
8.2 Troubleshooting Charts ....................................................................... 38
9.0 REPAIR PROCEDURES............................................................................... 57
9.1 Refrigeration System ............................................................................ 57
9.2 Replacing the Power Supply Board .................................................... 59
9.3 Replacing the Control/Display Board ................................................. 60
9.4 Replacing the Top Cover ..................................................................... 61
9.5 Replacing Thermostats ........................................................................ 62
9.6 Cleaning the Flow Switch..................................................................... 63
9.7 Replacement Parts ................................................................................ 64
9.8 Shipping/Repacking Instructions ......................................................... 64
10.0 REFERENCE TABLES ................................................................................. 65
10.1 Celsius-Fahrenheit Conversion ........................................................... 65
10.2 Temperature vs. Resistance ................................................................ 66
11.0 SERVICE INFORMATION .......................................................................... 67

SERVICE MANUAL
Medi-Therm®III
ii
FIGURES
ILLUSTRATIONS
Figure Description Page
1 Typical Warm-up Rate ................................................................................. 6
2 Typical Cooldown Rate ................................................................................. 6
3 Medi-Therm III System ................................................................................. 8
4 MT590 Test Tool ........................................................................................... 24
5 Initiating Service Mode 1 .............................................................................. 35
6A/6L Troubleshooting Charts ............................................................................... 38
6A Accessing RFU Codes ................................................................................... 38
6B RFU Code 1 .................................................................................................... 39
6C RFU Codes 2, 3, – , E, and L ......................................................................... 40
6D RFU Codes 4, 5 .............................................................................................. 41
6E RFU Codes 6, 7 .............................................................................................. 42
6F RFU Code 8 .................................................................................................... 43
6G RFU Code 9 .................................................................................................... 44
6H RFU Code H (page 1 of 2) ............................................................................ 46
6H RFU Code H (page 2 of 2) ............................................................................ 47
6I Check Water Flow Alert is On (page 1 of 2) ............................................. 48
6I Check Water Flow Alert is On (page 2 of 2) ............................................. 49
6J Pump Motor Not Running ............................................................................ 50
6K Blanket Won't Heat in Auto or Manual Mode (page 1 of 2).................... 52
6K Blanket Won't Heat in Auto or Manual Mode (page 2 of 2).................... 53
6L Blanket Will Not Cool (page 1 of 3)............................................................ 54
6L Blanket Will Not Cool (page 2 of 3)............................................................ 55
6L Blanket Will Not Cool (page 3 of 3)............................................................ 56
7 Flow Switch .................................................................................................... 63
8 Circuit Boards and Connectors (head)....................................................... 67
9A Operator Controls/Indicators ...................................................................... 68
9B Operator Controls/Indicators ...................................................................... 70
10 Heating Flow Diagram .................................................................................. 72
11 Cooling Flow Diagram .................................................................................. 72
12 Refrigeration Flow Diagram ........................................................................ 73
13 Test Setup ...................................................................................................... 74
14 Machine Disassembly .................................................................................... 75
15 Parts Diagram (base) .................................................................................... 76
16 Parts Diagram (head) ................................................................................... 78
17 Thermostat Wiring Diagram ....................................................................... 79
18 System Wiring Diagram ............................................................................... 81
19 Power Supply Board Schematic (sheet 1 of 3) .......................................... 82
20 Control/Display Board Schematic (sheet 2 of 3) ....................................... 83
21 Control/Display Board Schematic (sheet 3 of 3) ....................................... 84
22 Control/Display Board .................................................................................. 85
23 Power Supply Board ...................................................................................... 86
24 System Block Diagram ................................................................................. 87
25 Shipping/Repackaging Instructions ............................................................. 88

SERVICE MANUAL
Medi-Therm®III
1.0 PATIENT SAFETY Use the Medi-Therm III Hyper/Hypothermia machine only under the direction
of a physician.
Review the following precautions and procedures prior to each application:
WARNING
DANGER
•If the patient’s temperature is not responding or does not reach the
prescribed temperature in the prescribed time or deviates from the
prescribed temperature range, notify the attending physician
promptly. Failure to notify the physician promptly may
result in death or serious injury.
•Power interruption will cause the Medi-Therm III machine to go into
a standby mode, resulting in no therapy to the patient. Follow
instructions for desired mode to resume operation. Failure to
resume therapy could result in death or serious injury.
•The Medi-Therm III machine is provided with a means of checking
rectal/esophageal temperature probes. When performing the probe
check, use a disposable protective sheath (Becton-Dickinson catalog
3700 oral sheath or equivalent) on the probe. Failure to use
sheath could result in cross-contamination.
•A physician’s order is required for setting blanket temperature and
for continued use of equipment. At least every 20 minutes, or as
directed by a physician, check patient’s temperature and skin
condition of areas in contact with blanket; also, check blanket water
temperature. Pediatric, temperature-sensitive, and operating room
patients should be checked more frequently. Failure to monitor
patient may result in skin damage or inappropriate patient
temperature.
PEDIATRICS—The temperatures of infants and children are more
responsive to surface heating and cooling than adults. The smaller
the patient, the more pronounced the effect because of the patient’s
higher ratio of skin contact area to body mass.
TEMPERATURE-SENSITIVE PATIENTS—Patients with impaired
peripheral blood circulation caused by vascular diseases and patients
who are incapacitated may be more sensitive to temperature
changes than patients with more normal circulation.
OPERATING ROOM PATIENTS—Patients with poor circulation
associated with inadequate heart function, reduction in blood volume,
and constriction of peripheral blood vessels may deviate from the
normal response to the external application of heat and cold.
PATIENT SAFETY
Do not use the Medi-Therm III machine in the presence of flammable
anesthetics. Risk of explosion can result.
1

SERVICE MANUAL
Medi-Therm®III
WARNING
•Avoid placing additional heat sources between the patient and blanket.
Skin damage can result.
Heat applied by the blanket can result in a rise in skin temperature at
the areas of contact. The additional heat rise due to electrosurgical
currents flowing to the dispersive electrode could be sufficient to
cause tissue injury. Each thermal effect by itself may be completely safe,
but the additive effect may be injurious.1Keep additional heat sources
from between the patient and the blanket.
•Prevent excessive and/or prolonged tissue pressure and shearing
forces, especially over boney prominences. Skin damage may
result.
Localized skin injury due to tissue compressed between boney
prominences and fluid-filled channels has occurred during prolonged
cardiovascular procedures at blanket temperatures well below the
scientifically established epidermal burn injury threshold.2
Local ischemia can follow the application of pressures exceeding capil-
lary pressure resulting in tissue necrosis. This local effect may be en-
hanced by generalized impairment of the circulation, local shearing
forces and increased metabolic demand because of temperature eleva-
tion. Pathological changes may begin in two (2) hours.
•Keep the area between the patient and the blanket dry. Excessive
moisture may result in skin damage.
The application of heating or cooling may affect the toxicity of
solutions. Prep solutions have been reported to injure the skin when
allowed to remain between patients and water circulating heating
blankets during prolonged procedures.3
REFERENCES
1 Gendron, F. G. Unexplained Patient Burns. chap. 5, p. 87, Quest Publishing Co., 1988.
2 Scott, Stewart M. Thermal Blanket Injury in the Operating Room. Arch. Surg., vol. 94, p. 181, Feb. 1967; Crino, Marjanne H. Thermal
Burns Caused by Warming Blankets in the Operating Room. Clinical Workshop, vol. 29, pp. 149-150, Jan-Feb 1980; Gendron, Francis
G. Journal of Clinical Engineering, vol. 5, no. 1, pp. 19-26, January-March 1980; Moritz, A. R. and Henriques, Jr., F.C. Studies of
Thermal Injury II. The Relative Importance of Time and Surface Temperature in the Causation of Cutaneous Burns. Am. J. Path., 23:695,
1947; Stoll, Alice M. and Chianta, Maria A. Method and Rating System for Evaluation of Thermal Protection. Aerospace Medicine, vol.
40, no. 11, pp. 1232-1238, Nov. 1969; Stewart, T. P. and Magnano, S. Burns or Pressure Ulcers in the Surgical Patient. Decubitus, vol.
1, pp. 36-40, 1988.
3 Llorens, Alfred S. Reaction to povidone-iodine surgical scrub, scrub associated with radical pelvic operation. Am. J. Obstet. Gynecol., pp.
834-835, Nov. 14, 1974; Hodgkinson, Darryl J., Irons, George B. and Williams, Tiffany J., Chemical Burns and Skin Preparation
Solutions. Surgery, Gynecology & Obstetrics, vol. 17 pp. 534-536, Oct. 1978.
PATIENT SAFETY
1.0 PATIENT SAFETY
(continued)
CAUTION
•Place a dry absorbent sheet between the patient and the blanket
when using all-vinyl blankets.
A dry absorbent sheet placed between the patient and the Hyper/
Hypothermia Blanket will absorb perspiration. Vinyl blankets with
nonwoven fabric surfaces do not require an absorbent sheet when
using the nonwoven side toward the patient.
• Federal law restricts this device to sale by or on the order
of a physician.
2

SERVICE MANUAL
Medi-Therm®III
DANGER
MACHINE PRECAUTIONS
2.0 MACHINE
PRECAUTIONS Disconnect power before servicing unit.
Risk of electric shock.
WARNING
•Repairs should be performed only by qualified personnel such as
certified biomedical electronics technicians or certified clinical
engineers familiar with repair practices for servicing medical devices,
and in accordance with the Medi-Therm III Service Manual. Improper
repair may result in death or serious injury, equipment
damage, or malfunction.
•Always perform the FUNCTIONAL CHECK AND SAFETY INSPECTION
(section 7.3, p. 20) after making repairs and before returning the
Medi-Therm III machine to patient use. Improper repair may
result in death or serious injury, equipment damage, or
malfunction.
•Some manufacturer’s patient probes may contain compensation
resistors in series with YSI 400 series thermistors. Do not use these
probes with the Medi-Therm III machine. Inaccurate patient
temperature readouts will result and inappropriate therapy
may be delivered.
NOTE: Use YSI 400 series patient probes or equivalent.
(Refer to the list of recommended probes in section 5.0,
p. 7 PROBE INFORMATION.)
•Do not tip machine over without first draining the water out and
unplugging the power cord. Electrical shock or damage to the
machine can result.
Add distilled water only. Failure to use distilled water may result
in poor machine performance.
•Do not use alcohol, since it is flammable. Alcohol may also
accelerate blanket deterioration.
•Do not operate the machine without water, since damage to
internal components may result.
•Do not overfill. Overfilling may result in overflow because the water
in the blanket drains back into the machine when the machine is
turned off. Overfilling may also result in splashing from the overflow
tube during transport.
CAUTION
3

SERVICE MANUAL
Medi-Therm®III
3.0 REPAIR POLICY
3.1 IN-WARRANTY
REPAIRS
3.2 OUT-OF-WARRANTY
REPAIRS
The Medi-Therm III Hyper/Hypothermia machine is warranted free of defects in
material and workmanship for a period of two (2) years, under the terms and
conditions of the Gaymar warranty in place at the time of purchase. The
compressor portion of the machine carries a five (5) year prorated warranty. The
full warranty is available from Gaymar upon request. Medi-Therm III Hyper/
Hypothermia machines can be repaired at the factory or in the field. Upon
customer request, a shipping carton will be provided to safely return the machine
to Gaymar or a qualified Service Center.
For customers who repair Gaymar Medi-Therm III machines at their location, this
manual contains information to allow a qualified biomedical technician, familiar
with practices for servicing medical devices, to make necessary repairs. Service
training for the Hyper/Hypothermia machine is recommended and is available
from Gaymar. For specific details, contact your Gaymar representative or the
Technical Service Department at Gaymar. (See back cover of this manual for
Gaymar telephone numbers.)
All in-warranty field repairs must be authorized by Gaymar’s Technical Service
Department before proceeding.
The following repair options are available when local machine servicing is elected:
I . Defective Component
Replacement parts can be ordered. Specify the Gaymar part number; refer to
the Parts Lists in section 11, pp. 76–88 of this manual.
2. Defective Printed Circuit (PC) Board
Defective PC boards can be exchanged for replacement boards at a fixed
cost directly from the factory.
3. Defective Top Module
The defective top module can be returned (without base) to the factory for
repair.
4. Machine Repairs
If the Medi-Therm III machine becomes defective and the cause of the
problem cannot be determined, the complete machine can be returned to
the factory for servicing at the purchaser’s expense. This normally represents
the most expensive repair option.
Please contact Gaymar to obtain an RG (returned goods) number prior
to returning the machine.
REPAIRS / WARRANTY
4

SERVICE MANUAL
Medi-Therm®III
4.1 PHYSICAL SPECIFICATIONS
SPECIFICATIONS
4.2 THERMAL SPECIFICATIONS
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SERVICE MANUAL
Medi-Therm®III
4.2 THERMAL SPECIFICATIONS (cont'd)
4.3 ELECTRICAL SPECIFICATIONS
Figure 1—Typical warm-up rate
(with full size blanket)
Figure 2—Typical cooldown rate
(with full size blanket)
SPECIFICATIONS
WARM-UPRATE(typical)
Time (minutes)
Temperature (°C)
0
5
10
15
20
25
30
35
40
45
0 5 10 15 20 25
COOLDOWN RATE (typical)
Time (minutes)
Temperature (°C)
0
5
10
15
20
25
30
35
40
45
0 5 10 15 20 25
6
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SERVICE MANUAL
Medi-Therm®III
5.0 PROBE
INFORMATION
Disposable Probes
• DP400CE Disposable Rectal/Esophageal -
Adult/Small Child (3' [0.9 meters] long, requires adaptor);
YSI 400 series type
Reusable Probes
• PAT101 Patient probe—Rectal/Esophageal -
Adult (10' [3.0 meters] long); YSI 400 series type
• PAT102 Patient probe—Rectal/Esophageal -
Pediatric (10' [3.0 meters] long); YSI 400 series type
• PAT108 Patient probe—Skin surface (10' [3.0 meters] long);
YSI 400 series type
Probe Adaptor
• ADP10B Reusable adaptor cable for DP400: connects Gaymar
disposable probe to Gaymar or Cincinnati Sub-Zero
control unit.
PROBE INFORMATION
WARNING
Some manufacturer’s patient probes may contain compensation resistors
in series with YSI 400 series thermistors. Do not use these probes with
the Medi-Therm III machine.
Inaccurate patient temperature readouts will result and
inappropriate therapy may be delivered.
NOTE: Use YSI 400 series patient probes or equivalent.
(Refer to the list of recommended probes above.)
7

SERVICE MANUAL
Medi-Therm®III
Figure 3—Medi-Therm III System
MEDI-THERM®III SYSTEM
8

SERVICE MANUAL
Medi-Therm®III
THEORY OF OPERATION
The Gaymar Medi-Therm III machine provides a means of regulating patient
temperature by supplying temperature-controlled water through a connector
hose to a Gaymar Hyper/Hypothermia blanket. The blanket provides an interface
for heating or cooling the patient. A patient probe senses patient temperature,
which is displayed on the control panel. (See figure 3, p. 8.)
The Medi-Therm III machine controls output water temperature by mixing hot
and cold water using hot and cold solenoid valves under microcontroller control.
A circulating pump, heater and refrigeration unit are also utilized.
Bimetallic thermostats and associated backup circuitry limit output water
temperature independent of the microcontroller.
The feedback for control purposes depends upon the machine's operating mode.
The Medi-Therm III machine may be operated in one of three operating modes:
• In MANUAL mode, the operator sets the desired blanket temperature. A
temperature sensor within the machine monitors the water temperature and
the machine heats or cools the water as required to bring the blanket to the
SET POINT temperature. The patient temperature may be monitored by use
of a patient probe connected to the patient probe jack on the front of the
unit.
• In AUTO mode, the Medi-Therm III machine automatically regulates the
patient's temperature to the selected SET POINT. The machine constantly
compares actual patient temperature with the SET POINT value, and
automatically adjusts the blanket temperature so that the desired patient
temperature is achieved.
• In MONITOR mode, the operator can monitor patient temperature through
the patient probe, without providing therapy.
Hyperthermia/hypothermia blankets may be placed either under or over the
patient, depending upon the type of procedure. Some applications may require a
second blanket in order to achieve additional or more rapid heating or cooling.
For these situations, a second blanket may be connected to the Medi-Therm III
machine. The rate of patient heating or cooling may also be increased by
positioning half- and full-sized blankets so that greater body surface is in contact
with the blankets.
Whenever the machine is on, 10 quarts of water are maintained cold in the cold
water reservoir. A cold water reservoir probe provides temperature feedback to
the microcontroller which cycles the refrigeration unit on at 42.5°F (5.8°C) and
off at 38.0°F (3.3°C).
When the blanket water requires cooling, water is pumped from the cold water
reservoir. When the blanket water requires heating, a cartridge heater is used to
quickly heat the water.
6.0 THEORY OF
OPERATION, SYSTEM
9
6.1 THEORY,
MEDI-THERM III
MACHINE

SERVICE MANUAL
Medi-Therm®III
THEORY OF OPERATION
WATER TEMPERATURE CONTROL
Hot and cold solenoid valves regulate the flow path by directing water
returning from the blanket to either the hot or cold water reservoir. Regulating
the flow path controls the temperature of water pumped to the blanket. The
microcontroller controls solenoid valve operation. Only one valve may open at a
time:
When the HEAT status light is lit, the hot solenoid valve is open. Water
returning from the blanket circulates through the hot water reservoir
and is heated before being pumped back to the blanket. The heater,
pump, and hot solenoid valve are energized. (See fig. 10, p. 72.)
When the COOL status light is lit, the cold solenoid valve is open. Water
returns from the blanket to the cold water reservoir and is replenished
by chilled water from the cold water reservoir before being pumped
back to the blanket. The pump and cold solenoid valve are energized.
(See fig. 11, p. 72.) The refrigeration unit maintains the
cold water reservoir temperature and operates independently of the
solenoid status.
When the IN-TEMP status light is lit, either the blanket water temperature is
within 1.8°F (1°C) of the setpoint (in MANUAL mode) or the patient temperature
is within 1.8°F (1°C) of the setpoint (in AUTO mode). Water temperature is
controlled by alternating between heating and cooling (see figures 10–11) with
the heater cycled on and off as needed.
REFRIGERATION UNIT
The refrigeration circuit (see figure 12, p. 73) consists of two heat exchangers
operating at two pressures and two devices used to change these pressures. The
first of these devices is the compressor which changes the gas pressure from low
to high. The other device is the capillary tube which reduces the refrigerant
pressure from high to low.
Beginning the cycle at the capillary tube, high pressure liquid refrigerant flows in
the capillary tube and is discharged into the evaporator coil. The evaporator coil,
which is a heat exchanger, receives the refrigerant as a mixture of liquid and
vapor at a pressure low enough so that it boils and absorbs heat from the water
surrounding it.
The heated refrigerant vapor then leaves the evaporator coils, enters the suction
side of the compressor and is compressed, causing its pressure and temperature
to increase. The vapor, much warmer than the ambient air, travels to the
condenser.
The condenser is the other heat exchanger. The condenser fan draws the colder
ambient air over the condenser coils and removes the heat being carried by the
refrigerant and causes it to condense back into liquid refrigerant. This completes
the cycle and the high pressure liquid refrigerant is returned to the capillary tube
to be used over again. The temperature of the water surrounding the evaporator
coil (in the cold water reservoir) is controlled by the microcontroller. The
microcontroller senses the temperature with a cold water reservoir probe and
cycles the compressor relay on and off.
6.1 THEORY OF
OPERATION,
MEDI-THERM III
MACHINE (continued)
10

SERVICE MANUAL
Medi-Therm®III
THEORY OF OPERATION
BACKUP SYSTEMS
Backup systems within the Medi-Therm III machine limit the temperature of
water exiting the machine to specified ranges in the event of a failure of the
control system including the microcontroller:
Maximum water temperature is limited by two bimetallic thermostats. If
either of these two thermostats is actuated, a REMOVE FROM USE NOW /
MACHINE SHUTDOWN circuit is triggered which:
•shuts down the pump and heater;
•lights the ALERT and the REMOVE FROM USE NOW / MACHINE
SHUTDOWN indicators; and,
•sounds the audible alarm.
In addition, if the microcontroller is operational, the compressor shuts down, the
displays blank, and the ALERT indicator and audible alarm turn on and off.
Minimum water temperature is limited by a bimetallic thermostat. If this
thermostat is actuated, a REMOVE FROM USE NOW / MACHINE SHUTDOWN
circuit is triggered, which in turn:
•shuts down the pump and heater;
•lights the ALERT and the REMOVE FROM USE NOW / MACHINE
SHUTDOWN indicators; and,
•sounds the audible alarm. In addition, if the microcontroller is
operational, the compressor shuts down, the displays blank, and the
ALERT indicator and audible alarm turn on and off.
See figure 8, p. 67 for base-to-head and control/display board-to-power supply
board connections; figure 18, p. 81 for system wiring diagram; figures 19–21,
pp. 82–84 for electrical schematics; figures 22–23, pp. 85–86 for component
layouts and part designations; and figure 24, p. 87 for the system block diagram.
CONTROL/DISPLAY BOARD AND POWER SUPPLY BOARD
The Medi-Therm III machine uses two printed circuit boards (see figure 8, p. 67):
•The control/display board contains the microcontroller circuits, the
display circuits, and all other low voltage control circuits.
•The power supply board contains the power supply, the low voltage
to high voltage interface circuits, and the REMOVE FROM USE NOW
/ MACHINE SHUTDOWN backup safety circuits.
The control/display board connects to the patient probe jack J1 via P2 at J2 and
to the digital control assembly panel via P4 at J4. All other connections from the
system’s peripheral devices to the control/display board are made through the
power supply board.
A 26-pin cable connects the control/display board via P1 at J1 to the power
supply board via P3 at J4.
6.1 THEORY OF
OPERATION,
MEDI-THERM III
MACHINE (continued)
6.2 SYSTEM
COMPONENT
INTERCONNECTIONS
11

SERVICE MANUAL
Medi-Therm®III
THEORY OF OPERATION
Four cables connect the components in the base of the machine to the PC boards
in the head (see figure 8, p.67):
•A 9-pin connector P6 ties the blanket water probe RT2, cold water
reservoir probe RT1, flow switch S5, and level switch S4 to the power
supply board at J2 and ultimately to the control/display board.
•A 12-pin connector P7 ties the high voltage devices (pump, heater,
hot solenoid valve SV2, cold solenoid valve SV1, and refrigeration
compressor relay K1) to the interface circuits on the power supply
board, as well as thermostats S1, S2, and S3 to the high voltage backup
circuitry on the power supply board.
•A 6-pin connector P5 connects transformer T1 housed in the base
to the power supply circuitry at J3 on the power supply board.
•A chassis ground harness from the control/display board connects
to the chassis.
See figure 18, p.81 for the system wiring diagram; figures 19–21, pp. 82–84 for
the electrical schematics; figures 22–23, pp. 85–86 for component layouts and
part designations; and figure 24, p. 87 for the system block diagram.
Power enters the Medi-Therm III machine through circuit breaker CB1 to feed
the refrigeration unit through relay K1. It also then enters the power supply
board at J1 to feed the hot solenoid valve, cold solenoid valve, heater and pump
triacs, the high voltage backup water temperature limiting circuits and
transformer T1.
Power to drive the low voltage circuits on the control/display board is derived
from the machine’s power supplies which reside entirely on the power supply
board. The transformer T1 output is rectified and filtered to generate
unregulated positive and negative voltages. Q5, D1, L1 and associated
components are configured as a DC to DC switching regulator in a buck
configuration yielding a nominal output of +5.3 volts DC. Q6 is a linear regulator
with a nominal output of plus twelve (+12) volts DC, while Q7, also a linear
regulator, delivers a nominal output of minus twelve (-12) volts DC.
See figure 18, p. 81 for system wiring diagram; figures 19–21, pp. 82–84 for the
electrical schematics; figures 22–23, pp. 85–86 for component layouts and part
designations; and figure 24, p. 87 for the system block diagram.
The U37 microcontroller is fully dependent on the code stored in the U31
EPROM. When the machine is on, the microcontroller continually cycles through
its main program loop to perform the following:
•Thermistor output measurement (see section 6.4.1, p. 13)
•Digital control panel input (section 6.4.2, p. 13)
•Display update (section 6.4.3, p. 13)
•Peripheral input (section 6.4.4, p. 14)
•Blanket/Patient temperature control (section 6.4.5, p. 15)
•Cold water reservoir temperature control (section 6.4.6, p. 16)
Backup water temperature limiting is achieved independently of the
microcontroller. (See section 6.4.7, p. 16.)
6.2 SYSTEM
COMPONENT
INTERCONNECTIONS
(continued)
6.3 POWER SUPPLY
6.4 MACHINE
FUNCTIONS
12

SERVICE MANUAL
Medi-Therm®III
THEORY OF OPERATION
Temperature measurement is achieved using 400 series thermistor beads located
in the blanket water path (blanket water probe RT2), the cold water reservoir
(cold water reservoir probe RT1), and in the patient via the patient probe jack J1.
Under microcontroller U37 control, each of the three beads is connected to the
current source circuitry (U38 and associated components) by a demultiplexor
U49. At the same time, the resulting output voltage created by the current
through the thermistor is presented to an amplifier circuit (U39 and associated
components) via multiplexor U50. The amplified voltage is then applied to a
voltage-to-frequency converter U24. A frequency up to 100kHz is presented to
port pin P3.5 of the microcontroller. The microcontroller converts the incoming
frequency to a temperature value.
At regular intervals two compensation resistors R13 and R12 are also processed
in the same manner. These compensation resistors are precision resistors with
values at each end of the probe temperature range of 32°F (0°C) to 122°F
(50°C). The values from the precision resistors are used to compensate for
circuit drift.
User input is entered via a digital control panel. The input from the buttons is
decoded by U45. The “data available” line of U45 is tied to the microcontroller
port pin P3.3. When a button press is decoded and debounced by U45, the “data
available” line goes high and the microcontroller responds by inputting the
decoded value.
For display of measured and set point temperatures, 7 segment LED displays are
utilized:
•The set point display is driven by driver chip U48. The microcontroller
interfaces to it via the data bus at addresses 0FFF8H, 0FFF9H,
0FFFAH, 0FFFBH.
•The patient display is driven by driver chip U6. The microcontroller
interfaces to it via the data bus at addresses 0FFF4H, 0FFF5H, 0FFF6H,
0FFF7H.
•The blanket display is driven by driver chip U5. The microcontroller
interfaces to it via the data bus at addresses 0FFECH, 0FFEDH,
0FFEEH, 0FFEFH.
6.4.1 THERMISTOR
OUTPUT
MEASUREMENT
6.4.2 DIGITAL CONTROL
PANEL INPUT
6.4.3 DISPLAY UPDATE
13

SERVICE MANUAL
Medi-Therm®III
THEORY OF OPERATION
All alarm and status indicators are lit by LED bars driven by inverter/driver IC’s:
•The alarm latch U53 is the interface between the microcontroller
and the ALERT, ADD WATER, CHECK PROBE, CHECK FLOW, REMOVE
FROM USE NOW / MACHINE SHUTDOWN, SELECT, °F and °C drivers
via the data bus at address 0FFBFH. A high signal written to the
latch by the microcontroller activates the individual inverter/drivers
to light the corresponding indicator.
•The mode display latch U54 is the interface between the
microcontroller and the IN-TEMP, COOL, HEAT, FLOW-OK, AUTO,
MANUAL, and MONITOR drivers via the data bus at address 0FFDFH.
A high signal written to the latch by the microcontroller activates
the individual inverter/drivers.
•The control option display latch U64 is the interface between the
microcontroller and the GRADUAL, MODERATE, and RAPID drivers
via the databus at address FDFFH. A high signal written to the latch
by the microcontroller activates the individual drivers.
•The control latch U51 is the interface between the microcontroller
and the two leader light drivers via the data bus at address 0FF7FH.
When this latch is selected, a low signal on the data line from the
microcontroller causes a high signal on the latch output Therefore,
these two LED bar displays are “active low” in the eyes of the
microcontroller in contrast to all the other LED bar displays of the
machine.
The audible alarm is driven either by a high signal from the control latch U51
(from the microcontroller via the data bus at address 0FF7FH) or a high RFU IN
signal from Q10 on the power supply board. A low data line signal from the
microcontroller to U51 causes a high signal on the latch output. Therefore, the
alarm is “active low” in the eyes of the microcontroller. Transistor Q2 activates
the alarm.
The input buffer U55 is the interface between the microcontroller (via the data
bus at a “read” address of 0FFFEH) and the input signals from the flow switch S5
and the level switch S4 (which travel from the base through the power supply
board), the probe presence switch within the patient probe jack J1, and the
service mode button S3 on the control/display board. The lines to the buffer from
the peripheral devices are default high (via pull-up resistors).
The level switch S4 will pull its buffer input line low when it senses a sufficient
water level.
The flow switch S5 will pull its buffer input line low when it senses sufficient flow.
The probe presence switch within J1 will pull its buffer input line low when it
senses the presence of the patient probe.
Pressing the service mode switch S3 on the control/display board will pull its
buffer input line low.
6.4.3 DISPLAY UPDATE
(continued)
6.4.4 PERIPHERAL INPUT
14

SERVICE MANUAL
Medi-Therm®III
THEORY OF OPERATION
If the machine is in MANUAL mode, the blanket water temperature as sensed by
the blanket water probe is used as the feedback signal for controlling the water
temperature to the MANUAL mode set point temperature.
If the machine is in AUTO mode, the patient temperature as sensed by the patient
probe connected to the patient probe jack is used as the feedback signal for
controlling the patient temperature to the AUTO mode set point temperature.
The machine accomplishes this by adjusting the water temperature. When
cooling is required, the water temperature the machine uses in AUTO mode is
dependent on the CONTROL OPTION setting selected:
RAPID—the coldest water is used for cooling and the water temperature
used can be as low as 4°C.
MODERATE—cooling water temperature is limited to 15°C (27°F) below
the patient temperature.
GRADUAL—cooling water is limited to 10°C (18°F) below the patient
temperature.
For water temperature control, the microcontroller outputs a pulse train to each
solenoid valve and the heater. The pulse train duty cycle depends on the
magnitude and sense of the control signal calculated by the microcontroller. That
is, while the solenoids and heater are either on or off, the ratio of on time to off
time is proportional to the calculated control signal amplitude. For large
differences between set point and probe temperatures, the output to the cold
solenoid will be on and the output to the hot solenoid/heater combination will be
off, or vice-versa. For differences approaching zero, the output pulse train will be
applied to the hot solenoid and cold solenoid in a complementary fashion, with
the on times and off times automatically adjusted to maintain a probe
temperature equal to the set point, or the output pulse train will be applied to
the heater (with the hot solenoid remaining open), with the on times and off
times of the heater automatically adjusted to maintain a probe temperature equal
to the set point.
The circulating pump is energized whenever the unit is in AUTO or
MANUAL modes.
The control latch U51 on the control/display board is the interface between the
microcontroller (via the data bus at address 0FF7FH) and the peripheral drivers
on the power supply board.
Interface circuitry on the power supply board consists of U1, U2, U7, U8, Q3,
Q4, Q8, Q9, and associated components. U1, U2, U7, and U8 are optically
coupled triac drivers used to control their respective triacs (Q3, Q4, Q8, and
Q9); these combinations provide electrical isolation between the low voltage
microcontroller control circuits and the line voltage circuits.
The heater, pump, hot solenoid valve, and cold solenoid valve are individually
controlled by the microcontroller through latch U51 on the control/display
board. A high signal on the data line from the microcontroller causes a low signal
on the appropriate output line of U51 which then sinks current from the power
supply board to activate the peripheral devices.
6.4.5 BLANKET / PATIENT
TEMPERATURE
CONTROL
15