Gaymar MEDI-THERM II MTA5900 Series User manual

MEDI-THERM II
HYPER/HYPOTHERMIAMACHINE
MTA5900SERIES
SERVICE MANUAL
LISTED 303L
P/N 10187-000 7/98
www.gaymar.com P/N 10187-000 7/98

SERVICE MANUAL
Medi-Therm II
www.gaymar.com P/N 10187-000 7/98
Before you begin . . .
CAUTION
Federal law restricts this device to sale by
or on the order of a physician.
SAFETY PRECAUTIONS
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 II Service Manual.
•Always perform the FUNCTIONAL CHECK
AND SAFETY INSPECTION (section 7.3, p. 20)
after making repairs and before returning the
Medi-Therm II 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 II machine. Save all
packing material. Perform a visual and mechanical
inspection for concealed damage by removing the
wraparound from the chassis (see page 73). 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 II Service Manual for
additional details.
OPERATING INSTRUCTIONS
For information on operating the Medi-Therm II machine,
refer to the Medi-Therm II Operating Instructions.
Clik-Tite is a registered trademark of Gaymar Industries, Inc.
©1998. Gaymar Industries, Inc. All rights reserved.
Do not return the Medi-Therm II 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 II machine, remove
the compressor shipping brace. See p. 86, figure B.

SERVICE MANUAL
Medi-Therm II
www.gaymar.com P/N 10187-000 7/98
CONTENTS
i
CONTENTS
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
6 Operator Controls/Indicators ...................................................................69
7 Parts List (base) ..........................................................................................75
8 Parts List (head)..........................................................................................76
9 Control/DisplayBoard PartsList ................................................................83
10 Power Supply Board Parts List ...................................................................84
TABLES
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 & 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 ................................................... 60
9.3 Replacing the Control/Display Board ................................................ 61
9.4 Replacing the Top Cover.................................................................... 62
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 II
www.gaymar.com P/N 10187-000 7/98
ILLUSTRATIONS
ii
FIGURES
Figure Description Page
1 Typical Warm-up Rate ............................................................................... 6
2 Typical Cooldown Rate............................................................................... 6
3 Medi-Therm II 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
9 Operator Controls/Indicators .................................................................... 68
10 Heating Flow Diagram ................................................................................ 70
11 Cooling Flow Diagram ................................................................................ 70
12 Refrigeration Flow Diagram ....................................................................... 71
13 Test Setup .................................................................................................... 72
14 Machine Disassembly ................................................................................... 73
15 Parts Diagram (base)................................................................................... 74
16 Parts Diagram (head) .................................................................................. 76
17 Original Thermostat Wiring Diagram ...................................................... 77
17A New Thermostat Wiring Diagram ............................................................ 77
18 System Wiring Diagram ............................................................................. 79
19 Control/Display Board Schematic (sheet 1 of 2) ...................................... 80
20 Control/Display Board Schematic (sheet 2 of 2) ...................................... 81
21 Power Supply Board Schematic ................................................................ 82
22 Control/Display Board ................................................................................ 83
23 Power Supply Board.................................................................................... 84
24 Control/Display Board Block Diagram ...................................................... 85
25 Shipping/Repackaging Instructions ............................................................ 86

SERVICE MANUAL
Medi-Therm II
www.gaymar.com P/N 10187-000 7/98
1.0 PATIENT SAFETY Use the Medi-Therm II 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 II 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 II 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 II machine in the presence of
flammable anesthetics. Risk of explosion can result.
1

SERVICE MANUAL
Medi-Therm II
www.gaymar.com P/N 10187-000 7/98
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
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 tem-
perature elevation. 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 II
www.gaymar.com P/N 10187-000 7/98
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 II 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 II 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 YSI400 series thermistors. Do not use
these probes with the Medi-Therm II machine. Inaccurate
patient temperature readouts will result and
inappropriate therapy may be delivered.
NOTE: Use YSI400 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.
CAUTION
3

SERVICE MANUAL
Medi-Therm II
www.gaymar.com P/N 10187-000 7/98
3.0 REPAIR POLICY
3.1 IN-WARRANTY
REPAIRS
3.2 OUT-OF-WARRANTY
REPAIRS
The Medi-Therm II 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 II 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 II 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
Parts List in section 11, pp. 67 - 77 and 79 - 86 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 II 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 II
www.gaymar.com P/N 10187-000 7/98
4.1 PHYSICAL SPECIFICATIONS
SPECIFICATIONS
4.2 THERMAL SPECIFICATIONS
THERMAL SPECIFICATIONS
MTA5942 MTA5900 MTA5901
High Temperature Limits Fixed
(S2) & (S3)
111.2°F (44°C) to 120.2°F (49°C) 109.4°F (43°C) to 120.2°F (49°C) 109.4°F (43°C) to 120.2.°F (49°C)
(Machine will go into REMOVE FROM USE NOW / MACHINE SHUTDOWN condition and audible alarm will be on.)
Low Temperature Limits Fixed
(S1) 26.6°F (-3.0°C) to 36.5°F (+2.5°C) (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 Probe Activation
Temperature (whenever probe is
used) Below 89.6°F (32°C) or above 113°F (45°C)
Patient Temperature Control
Range for Automatic Mode 89.6°F (32°C) to 105.8°F (41°C)
Blanket Water Temperature
Control Range for Manual Mode 39.2°F (4°C) to 107.6°F (42°C) 39.2°F (4°C) to 105.8°F (41°C) 39.2°F (4°C) to 105.8°F (41°C)
4.0 SPECIFICATIONS
5
PHYSICAL SPECIFICATIONS
MTA5942 MTA5900 MTA5901
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 149 lb (full); 130 lb (empty); shipping wt, 164 lb
(72.1 kg (full); 62.6 kg (empty); shipping wt, 74.4 kg
Normal Reservoir
Operating Volume Approximately 10 quarts (9-1/2 liters) distilled water
Operating Ambient
Temperature Range 60°F to 90°F (15.6°C to 32.2°C) 60°F to 90°F (15.6°C to 32.2°C) 60°F to 80°F (15.6°C to 26.7°C)
Dead Head Pressure 8.5 psi max
(58.6 kPa max)
Flow * 16 gph (gallons per hour)
(60.6 liters/hour) * 16 gph (gallons per hour) (60.6 liters/hour) * 12 gph (gallons per hour) (45.4 liters/hour) *
* Minimum flow rates through a full size Gaymar Hyper/Hypothermia Blanket

SERVICE MANUAL
Medi-Therm II
www.gaymar.com P/N 10187-000 7/98
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
ELECTRICAL SPECIFICATIONS
MTA5942 MTA5900 MTA5901
Patient Temperature Measurement Accuracy ±0.5°C, ±0.9°F (using Gaymar 400 series probe)
Display Accuracy ±0.3°C, ±0.5°F
Display Resolution Blanket Water Temperature 1°C, 1°F
Patient Temperature 0.1°C, 0.1°F
Controller Accuracy Blanket Water Temperature ±0.8°C, ±1.4°F
Patient Temperature ±0.5°C, ±0.9°F
Current Leakage Chassis 100 microamps maximum
Patient Probe 50 microamps maximum
Input Voltage 120 ± 10 volts 120 ± 10 volts 100, +10, -5 volts
Frequency 60 Hz 60 Hz 50/60 Hz
Power Consumption 1125 watts 1125 watts 1150 watts
Input Current
with compressor and heater ON 11.5 amps 11.5 amps 13.0 amps
with compressor ON, heater OFF 8.5 amps 8.5 amps 8.8 amps
with heater ON, compressor OFF 5.0 amps 5.0 amps 6.0 amps

SERVICE MANUAL
Medi-Therm II
www.gaymar.com P/N 10187-000 7/98
5.0 PROBE
INFORMATION
Disposable Probes
• DP400 Disposable Rectal/Esophageal -
Adult/Small Child (3' [0.9 meters] long, requires adaptor);
YSI400 series type
Reusable Probes
• PAT101 Patient probe—Rectal/Esophageal -
Adult (10' [3.0 meters] long); YSI400 series type
• PAT102 Patient probe—Rectal/Esophageal -
Pediatric (10' [3.0 meters] long); YSI400 series type
• PAT108 Patient probe—Skin surface (10' [3.0 meters] long);
YSI400 series type
Probe Adaptor
• ADP10 Reusable adaptor cable for DP400: connects Gaymar
disposable probe to Gaymar or Cincinnati Sub-Zero
control unit for all applications that call for Baxter/Pharmaseal
No. 66N2700.
• ADP10B Reusable adaptor cable for DP400: connects Gaymar
disposable probe to American Medical Systems control unit or
all applications that call for Baxter/Pharmaseal
No. 66N27100.
PROBE INFORMATION
WARNING
Some manufacturer’s patient probes may contain compensation resistors
in series with YSI400 series thermistors. Do not use these probes with
the Medi-Therm II machine.
Inaccurate patient temperature readouts will result and
inappropriate therapy may be delivered.
NOTE: Use YSI400 series patient probes or equivalent.
(Refer to the list of recommended probes above.)
7

SERVICE MANUAL
Medi-Therm II
www.gaymar.com P/N 10187-000 7/98
Figure 3—Medi-Therm II System
control panel
YSI 400 series or equivalent
patient probe
connector hose
Medi-Therm II
machine
Hyper/Hypothermia
blanket
pinch
clamp
Clik-Tite connector
Quick-disconnects
o
n m
ac
hin
e
e
n
d
Clik-Tite connectors and
representative hose clamps
alternate
slide
clamp
®
MEDI-THERM II SYSTEM
8

SERVICE MANUAL
Medi-Therm II
THEORY OF OPERATION
www.gaymar.com P/N 10187-000 7/98
The Gaymar Medi-Therm II 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 II machine controls output water temperature by mixing hot
and cold water from two reservoirs using hot and cold solenoid valves under
microprocessor control. The feedback for control purposes is dependent on the
machine’s operating mode. A circulating pump, heater and refrigeration unit (all
under microprocessor control) are also utilized.
Bimetallic thermostats and associated backup circuitry limit output water
temperature independent of the microprocessor.
OPERATING MODES
The Medi-Therm II machine may be operated in one of three operating modes:
In MANUAL mode, the operator must observe patient temperature and
manually adjust the blanket water set point temperature. An inline blanket
water probe senses the temperature of the water pumped to the blanket and
provides feedback for control purposes to the microprocessor. The patient
temperature may be monitored by use of a patient probe.
In AUTO mode, the operator sets the desired patient temperature. The
patient’s temperature (as sensed by the patient probe) is automatically
regulated to this set point. The patient probe input provides feedback to the
microprocessor so it can adjust water temperature accordingly.
In MONITOR mode, the operator can monitor patient temperature through
the patient probe. No patient therapy is provided. The pump, heater, and hot
and cold solenoid valves are de-energized.
WATER RESERVOIRS
The hot water reservoir contains a small reserve of water. When the blanket
water requires heating, a cartridge heater under microprocessor control quickly
heats the water.
The cold water reservoir maintains approximately 10 quarts (91/2liters) of water
at approximately 39.2°F (4°C). A cold water reservoir probe provides
temperature feedback to the microprocessor which then cycles a refrigeration
compressor to control the reservoir temperature.
6.0 THEORY OF
OPERATION, SYSTEM
6.1 THEORY OF
OPERATION,
MEDI-THERM II
MACHINE
9

SERVICE MANUAL
Medi-Therm II
THEORY OF OPERATION
www.gaymar.com P/N 10187-000 7/98
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 microprocessor 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 figure 10, p.
70.)
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 figure 11, p. 70.) The refrigeration compressor
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 and 11).
REFRIGERATION UNIT
The refrigeration circuit (see figure 12, p. 71) 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 microprocessor. The
microprocessor senses the temperature with a cold water reservoir probe and
cycles the compressor relay on and off.
6.1 THEORY OF
OPERATION,
MEDI-THERM II
MACHINE (continued)
10

SERVICE MANUAL
Medi-Therm II
THEORY OF OPERATION
www.gaymar.com P/N 10187-000 7/98
BACKUP SYSTEMS
Backup systems within the Medi-Therm II machine limit the temperature of water
exiting the machine to specified ranges in the event of a failure of the control
system including the microprocessor:
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 microprocessor 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 microprocessor 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. 79 for system wiring diagram; figures 19, 20 and
21, pp. 80, 81, 82 for the electrical schematics; figures 22 and 23, pp. 83 and 84,
for component layouts and part designations; and figure 24, p. 85 for the
control/display board block diagram.
CONTROL/DISPLAY BOARD AND POWER SUPPLY BOARD
The Medi-Therm II machine uses two printed circuit boards (see figure 8, p. 67):
•The control/display board contains the microprocessor 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 II
MACHINE (continued)
6.2 SYSTEM
COMPONENT
INTERCONNECTIONS
11

SERVICE MANUAL
Medi-Therm II
THEORY OF OPERATION
www.gaymar.com P/N 10187-000 7/98
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.79 for the system wiring diagram; figures 19, 20 and 21, pp. 80,
81, 82 for the electrical schematics; figures 22 and 23, pp. 83, 84 for component
layouts and part designations; and figure 24, p. 85 for the control/display board
block diagram.
Power enters the Medi-Therm II 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. 79 for system wiring diagram; figures 19, 20 and 21, pp. 80, 81,
82 for the electrical schematics; figures 22 and 23, pp. 83, 84 for component
layouts and part designations; and figure 24, p. 85 for the control/display board
block diagram.
The U37 microprocessor is fully dependent on the code stored in the U31
EPROM. When the machine is on, the microprocessor 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
microprocessor. (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 II
THEORY OF OPERATION
www.gaymar.com P/N 10187-000 7/98
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 microprocessor 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 microprocessor. The microprocessor
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 microprocessor
port pin P3.3. When a button press is decoded and debounced by U45, the
“data available” line goes high and the microprocessor 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
microprocessor interfaces to it via the data bus at addresses 0FFF8H,
0FFF9H, 0FFFAH, 0FFFBH.
•The patient display is driven by driver chip U6. The microprocessor
interfaces to it via the data bus at addresses 0FFF4H, 0FFF5H,
0FFF6H, 0FFF7H.
•The blanket display is driven by driver chip U5. The microprocessor
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 II
THEORY OF OPERATION
www.gaymar.com P/N 10187-000 7/98
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 microprocessor
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 microprocessor activates the individual inverter/
drivers to light the corresponding indicator.
•The mode display latch U54 is the interface between
microprocessor 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 microprocessor activates
the individual inverter/drivers.
•The control latch U51 is the interface between the microprocessor
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
microprocessor causes a high signal on the latch output Therefore,
these two LED bar displays are “active low” in the eyes of the
microprocessor 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 microprocessor 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
microprocessor to U51 causes a high signal on the latch output Therefore, the
alarm is “active low” in the eyes of the microprocessor. NOR gate U40, driver
U26 and transistor Q1 work in conjunction to activate the alarm.
The input buffer U55 is the interface between the microprocessor (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.
* Some models do not have the °C/°F feature.
6.4.3 DISPLAY UPDATE
(continued)
6.4.4 PERIPHERAL INPUT
14

SERVICE MANUAL
Medi-Therm II
THEORY OF OPERATION
www.gaymar.com P/N 10187-000 7/98
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.
For water temperature control, the microprocessor control system outputs a
pulse train to each solenoid valve. The pulse train to the hot solenoid (and also
heater) is the complement of the pulse train to the cold solenoid. The pulse train
duty cycle depends on the magnitude and sense of the control signal calculated by
the microprocessor. That is, while the solenoids are each 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 each solenoid valve will be either on or off. For differences approaching
zero, the outputs to the solenoid valves (and heater) will switch on and off, with
the on and off times 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
microprocessor (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
microprocessor control circuits and the line voltage circuits.
The heater, pump, hot solenoid valve, and cold solenoid valve are individually
controlled by the microprocessor through latch U51 on the control/display
board. A high signal on the data line from the microprocessor 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.
Pin 11 of U51 on the control/display board and U8 and Q9 of the power
supply board control the cold solenoid valve while pin 9 of U51 on the
control/display board and U7 and Q8 of the power supply board control the
hot solenoid valve. Pin 8 of U51 on the control/display board and U2 and Q4
of the power supply board control the circulating pump. Pin 7 of U51 on the
control/display board and U1 and Q3 of the power supply board control
power to the heater.
6.4.5 BLANKET / PATIENT
TEMPERATURE
CONTROL
15

SERVICE MANUAL
Medi-Therm II
THEORY OF OPERATION
www.gaymar.com P/N 10187-000 7/98
The control latch U51 on the control/display board is the interface between
the microprocessor (via the data bus at address 0FF7FH) and the refrigeration
compressor relay driver on the power supply board. A high signal on the
appropriate data line causes a low signal at pin 6 of U51 on the control/display
board, which then activates Q12 on the power supply board. Q12 on the
power supply board is the interface between the control/display board and the
coil of the power relay K1 located in the machine base. The microprocessor
switches power through the relay to the refrigeration compressor at cut-out
and cut-in temperatures of 38°F (3.3°C) and 42.5°F (5.8°C). These
temperatures are sensed by the cold water reservoir probe RTl located in the
water reservoir. (See figure 12, p. 71.) Control of the cold water reservoir
temperature takes place whenever the machine is on.
The power supply board includes the REMOVE FROM USE NOW / MACHINE
SHUTDOWN circuitry, which includes U3, U4, U5, U6, U9, U10, D2, D3, Q1,
Q2, their interconnected components, and fixed, nonadjustable thermostats
S2, S3, and S1 located in the base. Under normal circumstances, Q1 and Q2
are kept turned on by the action of R7, C10, and D4 and R5, C15, and D5 to
complete the conduction path for the heater and pump. If the blanket water
falls into the low temperature limit range, S1 will open. If the blanket
temperature rises into the high temperature limits ranges, S2 and/or S3 will
open. (See section 4.2 Thermal Specification table, page 5, for the correct high
or low temperature limits with corresponding model number of your
machine.) When any one of these thermostats opens, it directly interrupts the
circuit and shuts off the pump and heater; at the same time, full line voltage
will appear between J1-2 and J1-3. In this case, U5 and U10 will be turned on
by the action of R4, D3, and associated parts while U3 and U9 will be turned
on by the action of R6, D2, and associated parts. U5 prevents Q2 from
turning on and U3 prevents Q1 from turning on even if the open
thermostat(s) closes again. The output of either U9 or U10, through buffer
Q10, signals the microprocessor that a thermostat has tripped and that a
REMOVE FROM USE NOW / MACHINE SHUTDOWN condition has resulted.
Thus, should any thermostat (S1, S2, or S3) trip, the heater and pump are
shut off and the microprocessor is notified.
On the control/display board, a high signal from Q10 of the power supply
board feeds NOR gate U40 to drive the audible alarm, feeds driver U52 to
light the REMOVE FROM USE NOW / MACHINE SHUTDOWN LED, and feeds
driver U11 to light the ALERT LED. All this is done independent of the
microprocessor. This same signal is sent to port pin P3.2 of the
microprocessor through C1, R1, and driver U11.
If the microprocessor is operational at the event of a high signal from Q10 of
the power supply board, the signal at P3.2 causes the microprocessor to shut
off the 7 segment displays, flash the ALERT LED and light the REMOVE FROM
USE NOW / MACHINE SHUTDOWN LED, toggle the audible alarm, store the
appropriate RFU* code indicating the reason for the shutdown, turn off the
heater and pump triacs Q3 and Q4, turn off the solenoid triacs Q8 and Q9,
and turn off the compressor transistor Q12. Anytime the microprocessor
6.4.6 COLD WATER
RESERVOIR
TEMPERATURE
CONTROL
6.4.7 BACK-UP WATER
TEMPERATURE
LIMITING
* RFU = REMOVE FROM USE NOW / MACHINE SHUTDOWN
16