Gaymar MTA7900 User manual

ALERT
To control temperature:WATER
To control temperature:PATIENT
•Connectbanket(s
)
•Inser tpatient
probe
•P ress button
Press againtoselect
Set desiredpatient
tempreature
AUTO
CONTROLOPTION
•
To monitor temperature:
•Insertpatientprobe
Press button
PATIENT
(NOTH ERAPY)
•MONITOR
SELECT MODE
SILENCE
ALARM
TEST LIGHTS
ANDALARM
CHECKWATER FLOW.
CHECK PATIENTPROBE.
ADDWATER.
REMOVEFROMUSE NOW
.
MACHINESHUTDOWN.
MANUAL
AUTO
MONITOR
TEMPERA
TURE
SetPoint
Water Patient
°C/°F
Warming Cooling
Flow-OK
•Connectbanket(s)
•P ress button
Setdesiredpatient
tempreature
MANUAL
•
MEDI-THERM®III
HYPER/HYPOTHERMIA MACHINE
MTA7900
SERVICE MANUAL
P/N 101251000 Rev A 04/10
www.gaymar.com

SERVICE MANUAL
Medi-Therm®III
SAFETY PRECAUTIONS
• Repairs should be performed only by qualied
personnel such as cert5ied biomedical
electronics technicians or certied 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.
Federal law restricts this device to sale by
or on the order of a physician.
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.
Do not return the Medi-Therm III machine to Gaymar
IndustrieswithoutrstcontactingGaymar’sTechnical
Service Department for assistance.
Telephone: Direct  (716)662-2551
TollFree 1800828-7341
IMPORTANT
Before operating the Medi-Therm III machine, remove the
compressor shipping braces. See p. 88, gure B.
OPERATING INSTRUCTIONS
For more 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.
©2010. Gaymar Industries, Inc. All right reserved. www.gaymar.com

SERVICE MANUAL
Medi-Therm®III
i
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Specications.......................................................... 5
 4.2 ThermalSpecications ........................................................ 5
 4.3 ElectricalSpecications ....................................................... 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
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

SERVICE MANUAL
Medi-Therm®III
ii
ILLUSTRATIONS
Figure Description .............................................................................. Page
 1 TypicalWaterWarm-upRate ................................................... 6
 2 TypicalWater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 WaterWon’tHeatinAutoorManualMode(page1of2) ... 52
 6K WaterWon’tHeatinAutoorManualMode(page2of2) ... 53
 6L WaterWillNotCool(page1of3).......................................... 54
 6L WaterWillNotCool(page2of3).......................................... 55
 6L Water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
FIGURES

SERVICE MANUAL
Medi-Therm®III
1
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:
• 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.
• When using the rate controlled Auto Moderate or Auto Gradual
modes for warming, switching to other modes, e.g.Auto Rapid or
Manual, or changing the temperature set point during the therapy
will cause the Medi-Therm to reset the therapy. Alternating
the Mode or Temperature set point may impact the
overalldurationofthetherapy.
•A physicians order is required for use of equipment. Check the
integrity of the skin according to department protocol when
regulating temperature with external devices. Frequency of
assessment and documentation will vary depending upon the
individual response of the patient. 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
ammable anesthetics. Riskofexplosioncanresult.

SERVICE MANUAL
Medi-Therm®III
2
• Avoid placing additional heat sources between the patient and blanket/
body wrap. Skindamagecanresult.
Heat applied by the blanket/body wrap can result in a rise in skin
temperature at the areas of contact.The additional heat rise due to
electrosurgical currents owing to the dispersive electrode could
be sufcient 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/body
wrap.
• 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 uid-lled channels has occurred during prolonged
cardiovascular procedures at water temperatures well below the
scientically established epidermal burn injury threshold.2
Local ischemia can follow the application of pressures exceeding
capillary pressure resulting in tissue necrosis.This local effect may be
enhanced 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/body wrap 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/body wraps 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 byWarming 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 ofThermal 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)
• Place a dry absorbent sheet between the patient and the blanket
when using the plastic-like side of any blanket.
A dry absorbent sheet placed between the patient and the Hyper/
Hypothermia Blanket will absorb perspiration.Vinyl blankets and
body wraps 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.

SERVICE MANUAL
Medi-Therm®III
3
MACHINE PRECAUTIONS
2.0 MACHINE
PRECAUTIONS Disconnect power before servicing unit.Riskofelectricshock.
• Repairs should be performed only by qualied personnel such as certied biomedical
electronics technicians or certied 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 only Gaymar probes or equivalentYSI 400 series probes approved for
use with medical devices.
(Refer to the list of recommended probes in section 5.0,
p. 7 PROBE INFORMATION.)
• All wire-lead, patient-connected transducer assemblies are subject to reading
error, local heating, and possible damage from high-intensity sources of RF energy.
Inadequately grounded electrosurgical equipment represents one such source, since
capacitively-coupled currents may seek alternate paths to ground through probe
cables and associated instruments. Patientburnsmayresult.
If possible, remove the probe from patient contact before activating the surgical unit or
other RF source. If probes must be used simultaneously with electrosurgical apparatus,
hazards can be reduced by selecting a temperature monitoring point which is remote
from the expected RF current path to the ground return pad.
• Do not tip machine over without rst 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 ammable. Alcohol may also accelerate blanket/body
wrap deterioration.
• Do not operate the machine without water, since damage to internal components
may result.
• Do not overll. Overlling may result in overow because the water in the blanket/
body wrap drains back into the machine when the machine is turned off. Overlling
may also result in splashing from the overow tube during transport.

SERVICE MANUAL
Medi-Therm®III
4
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 ve (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 eld. Upon
customer request, a shipping carton will be provided to safely return the machine
to Gaymar or a qualied Service Center.
For customers who repair Gaymar Medi-Therm III machines at their location, this
manual contains information to allow a qualied 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 specic 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 eld 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. 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

SERVICE MANUAL
Medi-Therm®III
5
4.1 PHYSICAL SPECIFICATIONS
SPECIFICATIONS
4.2 THERMAL SPECIFICATIONS
4.0 SPECIFICATIONS
MTA7900
Dimensions 37 in. high x 18-3/4 in. deep x 14 in. wide
(94.0 cm high x 47.6 cm deep x 35.6 cm wide)
Weight 141 lb (full); 121 lb (empty); shipping wt, 136 lb
64.0 kg (full); 54.9 kg (empty); shipping wt, 61.7 kg
Normal Reservoir Oper-
ating Volume Approximately 10 quarts (9-1/2 liters) distilled water
Operating Ambient Tem-
perature Range 15.6ºC to 32.2ºC (60ºF to 90ºF)
Dead Head Pressure 9.0 psi max (62 kPa max)
Flow 16 gph (gallons per hour) 60.6 liters/hour) *
High Temperature Limits Fixed
(S2) & (S3)
44ºC (111.2ºF) to 49ºC (120.2ºF)
(Machine will go into REMOVE FROM USE NOW / MACHINE SHUTDOWN
condition and audible alarm will be on)
Low Temperature Limits Fixed (S1)
-3ºC (26.6ºF) to +2.5ºC (36.5ºF)
(Machine will go into REMOVE FROM USE NOW / MACHINE SHUTDOWN
condition and audible alarm will be on)
Add Water Alert Actuation Less than 8 quarts (7.6 liters) of water in the cold reservoir
Check Water Flow Alert Actuation 6 GPH
Check Probe Activation Tempera-
ture (whenever probe is used) 29ºC (84.2ºF) or above 45ºC (113ºF)
Patient Temperature Control
Range for Automatic Mode 30ºC (86.0ºF) to 41ºC (105.8ºF)
Water Temperature Control Range
for Manual Mode 4ºC (39.2ºF) to 42ºC (107.6ºF)
* Minimum ow rate through a full size Gaymar Hyper/Hypothermia Blanket

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Medi-Therm®III
6
4.2 THERMAL SPECIFICATIONS (cont'd)
4.3 ELECTRICAL SPECIFICATIONS
Figure 1—Typical water warm-up rate
(with full size blanket)
Figure 2—Typical water cooldown rate
(with full size blanket)
SPECIFICATIONS
MTA7900
Patient Temperature Measurement Accuracy +0.5ºC, +0.9ºF
(using Gaymar 400 series probe)
Display Accuracy +0.3ºC, +0.5ºF
Display Resolution
Blanket Water Temperature 1ºC, 1ºF
Patient Temperature 0.1ºC, 0.1ºF
Controller Accuracy
Blanket Water Temperature
+0.8ºC, +1.4ºF
NOTE: At set points of 4ºC to 6ºC, this accuracy may not be
obtainable due to compressor control characteristics.
Patient Temperature +0.5ºC, +0.9ºF
Current Leakage
Chassis 100 microamps maximum
Patient Probe 50 microamps maximum
Input Voltage 120V + 10V
Frequency 60 Hz
Input Current 11.5A
Regulatory UL416
CSA C22.2 No. 125
Electromagnetic Compatibility
Meets EN60601-1-2:1993
(CISPR 11 Classied as Class A,
Group 1 ISM Equipment)
Debrillation Proof
The Medi-Therm III MTA7900 along with its temperature probe
is a “Debrillator Proof, Type BF Applied Part” per IEC60601-1
standards.

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Medi-Therm®III
7
5.0 PROBE
INFORMATION
DisposableProbes
• DP400CE Disposable Rectal/Esophageal -
Adult/Small Child (3' [0.9 meters] long, requires adaptor);
YSI 400 series type
ProbeAdaptor
• ADP10CE Reusable adaptor cable for DP400CE: connects Gaymar
disposable probe to Gaymar or Cincinnati Sub-Zero
control unit.
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 INFORMATION
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 only Gaymar probes or equivalentYSI 400 series probes
approved for use with medical devices.
(Refer to the list of recommended probes above.)

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Medi-Therm®III
8
MEDI-THERM®III SYSTEM
Figure 3 - Medi-Therm III System
Hyper/Hypothermia
blanket/body wrap
Gaymar probe or equivalent YSI 400 series probe
approved for use with medical devices.

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Medi-Therm®III
9
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/body wrap.The blanket/body wrap
provides an interface for heating or cooling the patient.A patient probe senses
patient temperature, which is displayed on the control panel. (See gure 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 water temperature. A
temperature sensor within the machine monitors the water temperature
and the machine heats or cools the water as required to bring the water
temperature 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 water 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.
Two gray hose sets are provided to connect multiple blankets and/or body wraps
in order to provide more body surface contact. Increased body surface contact
facilitates more efcient warming/cooling.
NOTE: When connecting a second blanket/body wrap to the Medi-Therm
III machine, check the water level prior to connecting the additional
blanket/body wrap.
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 5.8°C (42.5°F) and
off at 3.3°C (38.0°F).
When the water requires cooling, water is pumped from the cold water reservoir.
When the water requires heating, a cartridge heater is used to quickly heat the
water.
6.0 THEORY OF
OPERATION, SYSTEM
6.1 THEORY,
MEDI-THERM III
MACHINE

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Medi-Therm®III
10
WATER TEMPERATURE CONTROL
Hot and cold solenoid valves regulate the ow path by directing water
returning from the blanket/body wrap to either the hot or cold water reservoir.
Regulating the ow path controls the temperature of water pumped to the
blanket/body wrap.The microcontroller controls solenoid valve operation. Only
one valve may open at a time:
When the WARMING status light is lit, the hot solenoid valve is open.
Water returning from the blanket/body wrap circulates through the hot
water reservoir and is heated before being pumped back to the blanket/
body wrap.The heater, pump, and hot solenoid valve are energized. (See
g. 10, p. 72.)
When the COOLING status light is lit, the cold solenoid valve is open.
Water returns from the blanket/body wrap to the cold water reservoir
and is replenished by chilled water from the cold water reservoir
before being pumped back to the blanket/body wrap.The pump and
cold solenoid valve are energized. (See g. 11, p. 72.) The refrigeration
unit maintains the cold water reservoir temperature and operates
independently of the solenoid status.
When both the WARMING and COOLING lights are off, either the water
temperature is within 1°C (1.8°F) of the setpoint (in MANUAL mode) or the
patient temperature is within 0.5°C (0.9°F) of the setpoint (in AUTO mode).
Water temperature is controlled by alternating between heating and cooling (see
gures 10–11) with the heater cycled on and off as needed.
REFRIGERATION UNIT
The refrigeration circuit (see gure 12, p. 73) consists of two heat exchangers
operating at two pressures and two devices used to change these pressures.The
rst 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 ows
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)

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Medi-Therm®III
11
BACKUP SYSTEMS
Backup systems within the Medi-Therm III machine limit the temperature of
water exiting the machine to specied 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 gure 8, p. 67 for base-to-head and control/display board-to-power supply
board connections; gure 18, p. 81 for system wiring diagram; gures 19–21,
pp. 82–84 for electrical schematics; gures 22–23, pp. 85–86 for component
layouts and part designations; and gure 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 gure 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

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Medi-Therm®III
12
Four cables connect the components in the base of the machine to the PC boards
in the head (see gure 8, p.67):
• A 9-pin connector P6 ties the water temperature probe RT2, cold
water reservoir probe RT1, ow 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 gure 18, p.81 for the system wiring diagram; gures 19–21, pp. 82–84 for the
electrical schematics; gures 22–23, pp. 85–86 for component layouts and part
designations; and gure 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 rectied and ltered to generate unregulated
positive and negative voltages. Q5, D1, L1 and associated components are
congured as a DC to DC switching regulator in a buck conguration 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 gure 18, p. 81 for system wiring diagram; gures 19–21, pp. 82–84 for the
electrical schematics; gures 22–23, pp. 85–86 for component layouts and part
designations; and gure 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)
• Water/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

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Medi-Therm®III
13
Temperature measurement is achieved using 400 series thermistor beads located
in the water path (water temperature 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 amplier circuit (U39 and associated
components) via multiplexor U50. The amplied 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 0°C (32°F) to 50°C (122°F).
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 water temperature 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

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Medi-Therm®III
14
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,ADDWATER, 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 COOLING,WARMING, 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 ow 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 sufcient
water level.
The ow switch S5 will pull its buffer input line low when it senses sufcient ow.
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

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Medi-Therm®III
15
If the machine is in MANUAL mode, the water temperature as sensed by the
water temperature 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. The water
temperature the machine uses in AUTO mode is dependent on the CONTROL
OPTION setting selected and if COOLING or WARMING is desired.
When COOLING the patient:
RAPID - the coldest water is used for cooling - as low as 4°C (39°F). This may
not be the most comfortable setting for the patient.
MODERATE - Water temperature is limited to 15°C (27°F) below the patient's
temperature. This will provide an improved comfort setting to the patient.
GRADUAL - Water temperature is limited to 10°C (18°F) below the patient's
temperature.This will provide the optimal comfort setting to the patient.
When WARMING the patient:
RAPID - the highest allowable water temperature is used for warming - as
high as 42°C (107.6°F). This is the fastest warming mode the machine can
provide.
MODERATE - The patient temperature will increase at a rate of 1°C (1.8°F)
in a period of 3 hours (0.33°C/Hr [0.6°F/Hr]).
GRADUAL - The patient temperature will increase at a rate of 1°C (1.8°F) in
a period of 6 hours (0.17°C/Hr [0.3°F/Hr]).
When using AUTO MODERATE and AUTO GRADUAL for patient warming,
NO MANUAL INTERVENTION is required once the patient set point
temperature has been selected for warming.
When WARMING a patient in MODERATE or GRADUAL modes, water
temperature is limited to a maximum of 42.0°C (107.6°F) and a minimum which
is determined by the current control option selected 15.0°C [27°F] below the
patient temperature in MODERATE mode and 10.0°C [18°F] below the patient
temperature in GRADUAL mode).
If the patient temperature deviates from the warming rate specied by the
CONTROL OPTION selected (Moderate and Gradual only) by 1.0°C (1.8°F) the
following will occur:
• the PATIENT temperature will ash;
• the ALERT led will ash; and;
• the audible alarm will toggle
Once the patient temperature returns to within 1.0°C (1.8°F) of the warming
rate specied by the CONTROL OPTION selected, the PATIENT temperature and
ALERT light will stop ashing and the audible will silence.
NOTE: If the control MODE or SET POINT is changed while this alarm is
occuring, the alarm will be reset.
NOTE: If the control MODE or SET POINT is changed while in Auto-Gradual
or Auto-Moderate control mode, this may impact the overall time period
of the therapy depending on when in the hourly cycle the mode is inter
rupted. The therapy time duration is also dependent on the patient’s
temperature at the time the Auto-Moderate or Auto-Gradual control
modes are re-selected.
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.
6.4.5 WATER / PATIENT
TEMPERATURE
CONTROL