Gaymar MEDI-THERM III User manual

MEDI-THERM ®III
HYPER/HYPOTHERMIA MACHINE
REF MTA7912
P/N 100909000 Rev B 11/09
SERVICE MANUAL
MANUA
L
Flow-OK

MTA7912 Service Manual
Important
• Refer to the Medi-Therm®III Operator’s Manual for detailed
operating instructions. Read and understand the Operator’s
Manual and all precautions prior to using the Hyper/
Hypothermia machine.
• Review the SAFETY PRECAUTIONS (see page 1) prior to
servicing the Medi-Therm III machine.
• For technical assistance, contact your local dealer.
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 gure 18, page 57). 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 2.0 of this Medi-Therm III Service Manual for
additional details.
IMPORTANT
Before operating the Medi-Therm III machine, remove the
compressor shipping braces. See p. 74, gure B, items 8 and 9.
Temporarily remove the power cord retainer (g. 19, p. 58, item 6)
and install the power cord. Reattach the power cord retainer.
Before you begin . . .
Gaymar®and Clik-Tite® are registered in the U. S. Patent and Trademark Ofce.
Gaymar®, Clik-Tite®, and Medi-Therm®are trademarks of Gaymar Industries, Inc.
© 2009. Gaymar Industries, Inc. All rights reserved.
Table of Contents
1.0 Safety Precautions.................................... 1
2.0 Repair Policy............................................. 2
3.0 Specications............................................ 3
4.0 Blankets/Body Wraps/Accessories........... 6
5.0 Operator Control Panel............................. 8
6.0 Theory of Operation................................ 10
7.0 Functional Check, Safety Inspection,
and Preventive Maintenance .................. 17
8.0 Service Modes and Troubleshooting ...... 23
9.0 Repair Procedures.................................. 47
10.0 Service Information................................. 52
Figures
1 Water Warm-up Rate................................ 4
2 Water Cooldown Rate............................... 4
3 Disposable Probe/Reusable Cable........... 6
4 Medi-Therm III System ............................. 7
5 Medi-Therm III Control Panel.................... 9
6 Probe Check Well................................... 18
7 Functional Check/Inspection Form ......... 22
8 Initiating Service Mode 1 ........................ 23
9 RFU Codes............................................. 24
10A-N Troubleshooting Charts ..................... 27-46
11 Connecting Terminal Block Wires........... 49
12 Flow Switch............................................. 51
13 Temperature vs. Resistance Table.......... 52
14 Circuit Boards/Connectors (Head).......... 53
15A/B Heating Flow; Cooling Flow.................... 54
16 Refrigeration Flow Diagram.................... 55
17A/B Test Setup; Test Setup (alternate)........... 56
18 Machine Disassembly............................. 57
19 Parts Diagram (Base), Parts List ............ 58
20 Parts Diagram (Head), Parts List............ 60
21 Thermostat Wiring Diagram.................... 61
22 Control/Display Board, Parts List............ 62
23 Power Supply Board, Parts List.............. 64
24 Alarm/Backup Board, Parts List.............. 66
25 Wiring Diagram [foldout] ......................... 68
26 Power Supply Board Schematic,
1 of 4 [foldout]......................................... 69
27A Control Display Board Schematic,
2 of 4 [foldout]......................................... 70
27B Control Diplay Board Schematic,
3 of 4 [foldout]......................................... 71
28 Alarm/Backup Board Schematic,
4 of 4 [foldout]......................................... 72
29 Block Diagram [foldout]........................... 73
30 Shipping Instructions [foldout]................. 74

MTA7912 Service Manual
1.0 Safety Precautions
Review the following safety precautions prior to testing the
Medi-Therm III machine:
Risk of electric shock. Refer servicing
to qualied medical equipment service
personnel.
• Repairs should be performed only by qualied medical
equipment service personnel and in accordance with
this Service Manual. Otherwise, damage to the
Medi‑Therm III machine and improper therapy may
result.
• 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.
• Use only Gaymar probes (see Accessories, page 6) or
equivalent YSI 400 series probes approved for use with
medical devices in the Patient Probe jack.
Use of other probes could result in erroneous
patient temperature values.
• 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. Altering the Mode
or Temperature set point may impact the overall
duration of the therapy.
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.
• For grounding reliability, plug the Medi-Therm III
machine only into a properly grounded outlet.
• To prevent damage to the power cord, always keep
the power cord retainer in place.
Machine Precautions
DANGER
WARNING
CAUTION
1

MTA7912 Service ManualRepairs/Warranty
2.0 Repair Policy
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 can be
arranged through your local dealer.
2.1 Limited Warranty
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 year prorated warranty. During the warranty
period, contact your local dealer.
Warranty does not cover products abused, misused, or altered
outside the factory. There are no obligations on the part of
Gaymar for consequential damages arising out of or in connection
with the use or performance of the product. Gaymar disclaims
all implied warranties including, but not limited to, the implied
warranties of merchantability and of tness for a particular
purpose.
2.2 Warranty Repairs
All in-warranty eld repairs must be authorized by Gaymar’s
Export Department before proceeding.
2.3 Out-of-Warranty Repairs
The following repair options are available when local machine
servicing is elected:
I . Defective Component
Replacement parts can be ordered from your local dealer.
Specify the Gaymar part number; refer to the Parts Lists in
section 10.0 of this manual.
2. Defective Printed Circuit (PC) Board
Defective PC boards can be exchanged for replacement
boards at a xed cost directly from your local dealer.
3. Defective Head
The defective head module can be returned (without base)
for repair. Contact your local dealer for information.
4. Machine Repairs
If the Medi-Therm III machine becomes defective and the
cause of the problem cannot be determined, the complete
machine can be returned to your local dealer for servicing at
the purchaser’s expense. This normally represents the most
expensive repair option. Contact your local dealer.
2
2.4 Return Authorization
Please contact your local dealer.

MTA7912 Service Manual
3.0 Specications
3.1 Physical
Specications
3.2 Thermal
3
ModelMTA7912
Dimensions 94 cm high x 48 cm deep x 36 cm wide
Weight 76.3 kg (full); 68.6 kg (empty)
Normal Reservoir Operating Volume 9.5 liters distilled water
Operating Ambient Temperature Range
15.6°C to 32.2°C
Power Loss Indicator Battery 8.4V NiMH
RefrigerantHFC-134a; 0.234 kg (8.25 oz.)
Fuse (stepdown transformer) 5 mm x 20 mm T, 6.3 A, 250 V, L
Physical Specifications
High Temperature Limits Fixed
Backup System 1 - Overtemperature probe RT3
41.1°C to 43.6°C (Machine will go into a REMOVE FROM USE
NOWshutdown condition and the alarm will be on.)
High Temperature Limits Fixed
Backup System 2 - Thermostat S2
44°C to 49°C (Machine will go into a REMOVE FROM USE
NOWshutdown condition and the alarm will be on.)
Low Temperature Limits Fixed
Backup System 2 - Thermostat S1
-3.0°C to 2.5°C (Machine will go into a REMOVE FROM USE
NOWshutdown condition and the alarm will be on.)
Add Water Alert Actuation
Less than 7.6 liters of water in the cold reservoir
Check Patient Alert Activation Temperature
(whenever probe is used)
Below 29°C or above 40°C
Machine Ceases Therapy (whenever probe is used)
Below 29°C or above 45°C
Patient Temperature Control Range for
PATIENT CONTROL mode
30°C to 39°C
Patient Temperature Control Range for
BLANKET CONTROLmode
4°C to 41°C
Flashing Temperature Display
(with setpoint 30°C or greater)
·BLANKET CONTROL MODE: Actuates when actual temperature
is not within 1.0°C of setpoint 4 hours after powerup, 4 hours after
a setpoint change, or 10 minutes after the first instance of the
actual temperature becoming equal to the setpoint.
·PATIENT CONTROL MODE (except warming a patient in
MODERATE or GRADUAL mode): Actuates when actual
temperature is not within 0.5°C of setpoint 4 hours after powerup
or 4 hours after a setpoint change.
·PATIENT CONTROL MODE (warming a patient in MODERATE or
GRADUAL mode only): Actuates when actual temperature is not
within 1.0°C of the desired warming rate. See section 6.4.5, p. 14.
Thermal Specifications

MTA7912 Service ManualSpecications
3.3 Performance
Patient Temperature Measurement
Accuracy
± 0.4°C (using Gaymar disposable probe)
± 0.3°C (using Gaymar reusable probe)
Display Accuracy ± 0.2°C
Display Resolution
WATER TEMPERATURE
0.1°C
Display Resolution
PATIENT TEMPERATURE
0.1°C
Controller Accuracy
WATER TEMPERATURE
± 0.8°C
Controller Accuracy
PATIENT TEMPERATURE
± 0.5°C
Flow* 60.6 liters per hour
Performance Specifications
* Minimum flow rates through a full size Gaymar Hyper/Hypothermia Blanket
4
3.2 Thermal (continued)
Figure 1—Typical water warm-up rate
(with full size blanket)
Figure 2—Typical water cooldown rate
(with full size blanket)
WARM-UP RATE (typical)
0
5
10
15
20
25
30
35
40
45
0510 15 20 25
Time (minutes)
Temperature (°C)
COOLDOWN RATE (typical)
0
5
10
15
20
25
30
35
40
45
0510 15 20 25 30
Time (minutes)
Temperature (°C)

MTA7912 Service Manual
3.4 Electrical
3.6 Classication
3.5 Regulatory
Current Leakage, Earth
Neutral closed
Neutral open
175 microamps maximum
125 microamps maximum
Current Leakage, Patient Probe
Neutral closed
Neutral open
100 microamps maximum
100 microamps maximum
Voltage ~220 V to ~240 V ± 10%
Frequency 50 Hz
Power Consumption Capacity 1575 VA
Current 6 A
Detachable Power Cord
Use only an International (harmonized) three-wire
cordset using cordage approved to HD-21.
Conductor size is 1.00 mm2(H05VVF3G1.00).
Electrical Specifications
Classification
● EN60601-1 Class 1, grounded, not suitable for use in the
presence of flammable anesthetic mixture with air or
with oxygen or nitrous oxide. Not classified for protection
against harmful ingress of liquid.
● EN60601-1-2, Class A, CISPR 11, emission requirements.
● EN60601-2-35
5
Specications
Regulatory Medical Device Directive (93/42/EEC) Class IIb (indicated by CE mark)

MTA7912 Service Manual
6
4.0 Blankets/Body Wraps/Accessories
Single Patient Use Blankets,
Polymer with Nonwoven Fabric
REF DHP810 O.R. Table and General Use
(64 cm x 163 cm)
REF DHP812 Pediatric General Use
(56 cm x 84 cm)
REF DHP813 Adult General Use
(76 cm x 163 cm)
Single Patient Use Blankets, All Vinyl
REF DHP901 Adult General Use
(64 cm x 175 cm)
REF DHP902 Pediatric General Use
(64 cm x 91 cm)
Reusable Blankets, All Vinyl
REF HP7010 Adult General Use
(64 cm x 175 cm)
REF HP7020 Pediatric General Use
(64 cm x 91 cm)
Single Patinet Use Torso Wraps, Polymer with
Nonwoven Fabric
REF DHV530 Small/Medium
REF DHV535 Large
Single Patinet Use Leg Wraps, Polymer with
Nonwoven Fabric
REF DHL540 One size ts all
All blankets require use of the reusable DBK35CE
Connector Hose.
Accessories *
(see item 1, p. 59) Detachable Power Cords
REF DBK35CE Connector Hose (3 meters)
REF PAT101CE Reusable Adult Patient Probe (3 meters)
Rectal/Esophageal
REF PAT102CE Reusable Pediatric Patient Probe (3 meters)
Rectal/Esophageal
REF PAT108CE Reusable Patient Probe (3 meters)
Skin Surface
REF DP400CE Disposable Adult and Pediatric Patient
Probe (0.9 meter) Rectal/Esophageal
[requires ADP10CE Adaptor Cable]
REF ADP10CE Reusable Probe Adaptor Cable
(3 meters) for DP400CE Probe
* These Gaymar probes, adapters, and hoses should be
used only with Gaymar Hyper/Hypothermia Machines.
ADP10CE DP400CE
MTA7912
Blankets/Body Wraps/Accessories
Figure 3—Disposable Probe/Reusable Adaptor Cable

MTA7912 Service Manual
Water Fill Opening
Lift cover. Fill unit with
distilled water until green
band on oat is fully visible.
Dual Blanket/Body Wrap
Connections with Quick‑
disconnects and
Probe Check Well
Use PROBE CHECK
well to verify the
integrity of the
patient probe.
Figure 4—Medi-Therm III Hyper/Hypothermia System
Medi-Therm III
machine
control panel
Gaymar probe or equivalent YSI
400 series probe approved for use
with medical devices.
Hyper/Hypothermia
blanket/body wrap
ON/OFF Switch
(Circuit Breaker)
Controls power to
Medi-Therm III.
Patient Probe Jack
Accepts patient probe plug connecting patient
probe to machine. Use only Gaymar probes
or equivalent YSI 400 series probes approved
for use with medical devices.
Medi-Therm III System
7

MTA7912 Service ManualOperator Control Panel
MACHINE STATUS
FLOW‑OK indicates water is owing adequately.
WARMING indicates the machine is heating.
COOLING indicates the machine is cooling.
TEST LIGHTS ashes all indicator lights and
digital displays, while sounding an audible alarm.
ALARM SILENCE temporarily silences the
audible alarm. The audible alarm will reactivate in
10 minutes if the condition persists.
ALERTS
CHECK FLOW indicates the ow of water to the
blanket/body wrap has been restricted.
NOTE: When two gray hose sets are in use, the
CHECK FLOW alarm will only sound if the ow
through BOTH gray hose sets is occluded.
CHECK PATIENT indicates the patient probe is
sensing an abnormal patient temperature (below
29°C or above 40°C). It may indicate the patient
probe has become dislodged, an incorrect probe
is being used, or a probe has become defective.
An audible alarm accompanies this alert.
ADD WATER indicates the water reservoir is
lled to less than the recommended level.
REMOVE FROM USE NOW indicates
the Medi-Therm III machine has shut down due
to a malfunction.
Remove the machine from use. Contact
qualied medical service personnel.
FLASHING DISPLAY indicates that the water
or patient temperature is not being maintained
within the acceptable limits of the set point
temperature. It is accompanied by an audible
alarm. See section 3.2 for explanations of the
various alarms that have a ashing temperature
display.
POWER LOSS INDICATOR lights when
power is removed and ON/OFF circuit breaker
is ON. [located on front of machine]
5.0 Operator Control Panel
See gure 5, page 9.
8

MTA7912 Service Manual Operator Control Panel
Figure 5—Medi-Therm III Control Panel
® ®
SELECT MODE
BLANKET CONTROL—
Adjust SET POINT to control water
temperature.
(4°C to 41°C)
PATIENT CONTROL—
Connect patient probe, then adjust
SET POINT to control patient
temperature.
(30°C to 39°C)
CONTROL OPTION—
Cooling/Warming adjusted to
RAPID rate.
Cooling/Warming adjusted to
MODERATE rate.
Cooling/Warming adjusted to
GRADUAL rate.
MONITOR ONLY—
Connect patient probe, then use to
monitor patient temperature. No
therapy is provided.
TEMPERATURE
WATER TEMPERATURE—
This display lights when either PATIENT
CONTROL or BLANKET CONTROL is selected.
PATIENT TEMPERATURE—
As measured by the patient probe.
This display lights whenever a patient probe is
plugged in.
SET POINT CHANGE—
Press the “q” or “p” button to select machine
set point. When selecting a temperature outside
the normothermic range (36°C to 38°C), an
audible alarm will chime. Press and hold the
“q” or “p” button until the chime stops to
access the extended temperature range.
PATIENT PROBE JACK—
Insert only a Gaymar probe or an equivalent
YSI 400 series probe approved for use with
medical devices. [located on front of machine]
9

MTA7912 Service ManualTheory of Operation
6.0 Theory of Operation, System
The Gaymar Medi-Therm III machine provides a means of regu-
lating 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 g. 4,
p. 7 and g. 5, p. 9.)
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.
Two backup systems limit output water temperature independent
of the main microcontroller.
The feedback for control purposes depends upon the machine’s
operating mode. The machine may be operated in one of three
operating modes:
• In BLANKET CONTROL 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 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 PATIENT CONTROL 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 ONLY mode, the operator can monitor
patient temperature through the patient probe, without
providing therapy.
Hyperthermia/hypothermia blankets/body wraps may be placed
either under, over or around the patient, depending upon the type
of procedure. Two gray hose sets are provided to connect multiple
blankets and/or body wraps in order to provide more body surface
contact. Increasing body surface contact facilitates more efcient
warming/cooling.
In the event of a power loss, a battery backup circuit will light the
POWER LOSS light and sound the audible alarm. Upon restoring
power, the mode of operation and the set points will have to be
reselected.
6.1 Theory, Medi-Therm III Machine
Whenever the machine is on, 9.5 liters of water are maintained
cold in the cold water reservoir. A cold water reservoir probe
provides temperature feedback to the main microcontroller which
cycles the refrigeration unit on at 5.8°C and off at 3.3°C.
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.
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 main
microcontroller controls solenoid valve operation. Only one valve
operates 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 gure 15A, page 54.
•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 gure 15B,
page 54. The refrigeration unit maintains the cold water
reservoir temperature and operates independently of
the solenoid status.
•When the both the WARMING and COOLING lights are
OFF, either the water temperature is within 1.0°C of the
setpoint (in BLANKET CONTROL mode) or the patient
temperature is within 0.5°C of the setpoint (in PATIENT
CONTROL mode). Water temperature is controlled by
alternating between heating and cooling (see gs. 15A
and 15B, p. 54).
REFRIGERATION UNIT
The refrigeration circuit (see g. 16, p. 55) 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
10

MTA7912 Service Manual
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 main microcontroller. The microcontroller senses
the temperature with a cold water reservoir probe and cycles the
compressor relay on and off.
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 main
controller:
• BACKUP SYSTEM I (PIC Microcontroller and probe)
The rst backup system is independent of the main
microcontroller. It runs off its own power supply. It limits
the temperature of water exiting the machine in the
event of a failure of control circuitry (including the main
microcontroller). Using an overtemperature probe in
the same water path as the main microcontroller water
temperature probe, water temperature is sensed. When
limit temperatures are surpassed the PIC sends a signal
to trigger an analog REMOVE FROM USE NOW circuit,
which:
•shuts down the pump and heater
•lights the ALERT and the REMOVE FROM USE
NOW indicators; and,
•sounds the audible alarm.
In addition, if the main microcontroller is operational,
the compressor shuts down, the displays blank, and
the ALERT indicator and audible alarm turn on and off.
The power supply for this system is backed with a nickel
hydride battery to provide a minimum 10 minute audible
and visual POWER LOSS indication in the event of
power failure.
• BACKUP SYSTEM II (Thermostats)
The second backup system is independent of both the
main microcontroller and the rst backup system. It
limits the temperature of water exiting the machine in
the event of a failure of control circuitry (including the
main microcontroller). This is accomplished using two
bimetallic thermostats. If either of these two thermostats
is actuated, they open the heater circuit directly and
trigger an analog REMOVE FROM USE NOW circuit
(separate from BACKUP SYSTEM I), which:
•shuts down the pump and heater
•lights the ALERT and the REMOVE FROM USE
NOW indicators; and,
•sounds the audible alarm.
In addition, if the main microcontroller is operational,
the compressor shuts down, the displays blank, and the
ALERT indicator and audible alarm turn on and off.
6.2 Theory, System Component Interconnections
See gure 14, p. 53 for base-to-head and control/display
board-to-power supply board connections; gure 25, p. 68 for the
system wiring diagram; gures 26-28, pp. 69-72 for the electrical
schematics; gures 22-24, pp. 62-67 for component layouts
and part designations; and gure 29, p. 73 for the system block
diagram.
CONTROL/DISPLAY BOARD, ALARM/BACKUP BOARD, AND
POWER SUPPLY BOARD
The Medi-Therm III machine uses three printed circuit boards
(see gure 14, p. 53):
• The control/display board contains the main
microcontroller circuits, the display circuits, and all other
low voltage control circuits.
• The alarm/backup board contains the BACKUP
SYSTEM I microcontroller circuits, POWER LOSS
indicator circuits and its own power supply.
• The power supply board contains the main
microcontroller power supply, the low voltage to high
voltage interface circuits, and the REMOVE FROM USE
NOW latching 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
J4A. 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.
Five cables connect the components in the base of the machine
to the PC boards in the head (see gure 14, p. 53):
• 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
Theory of Operation
11

MTA7912 Service ManualTheory of Operation
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 and S2 to the high voltage latching
circuitry on the power supply board, at J1 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 6‑pin connector P11 connects the over-temperature
probe RT3 and auxiliary switch within the circuit breaker
CB1 (for sensing POWER LOSS) to the alarm/backup
board at J4.
• A chassis ground harness from the control/display
board and alarm/backup board connects to the chassis.
6.3 Theory, Main Microcontroller Power Supply
See gure 25, p. 68 for the system wiring diagram; gures 26-28,
pp. 69-72 for the electrical schematics; gures 22-24, pp. 62-67
for component layouts and part designations; and gure 29, p. 73
for the system block diagram.
Power enters the Medi-Therm III machine through circuit breaker
CB1 to feed the refrigeration unit (through relay K1) and the
stepdown transformer T2. The output of T2 is fused with a 6.3
amp fuse located below the TB1 terminal block; see gure 19,
item 22. Stepped down voltage from T2 then enters the power
supply board at J1 to feed the hot solenoid valve, cold solenoid
valve, heater and pump triacs, the high voltage latching circuits
and transformer T1.
Power to drive the low voltage circuits on the control/display board
is derived from the machine’s main microcontroller 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.
6.4 Theory, Machine Functions
See gure 25, p. 68 for system wiring diagram; gures 26-28, pp.
69-72 for the electrical schematics; gures 22-24, pp. 62-67 for
component layouts and part designations; and gure 29, p. 73 for
the system block diagram.
The main microcontroller U37 is fully dependent on the code
stored in the U31 EPROM. When the machine is on, the main
microcontroller continually cycles through its main program loop
to perform the following:
• Thermistor output measurement (see section 6.4.1)
• Digital control panel input (section 6.4.2)
• Display update (section 6.4.3)
• Peripheral input (section 6.4.4, p. 13)
• Blanket/Patient temperature control (section 6.4.5, p. 13)
• Cold water reservoir temperature control (section 6.4.6,
p. 14)
Backup water temperature limiting is achieved independently of
the microcontroller. See section 6.4.7, page 14.
6.4.1 Thermistor Output Measurement
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.
The main microcontroller connects each of the three beads to the
current source circuitry (U38 and associated components) using
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 to 50°C. The values from the
precision resistors are used to compensate for circuit drift.
6.4.2 Digital Control Panel Input
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 main 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.
6.4.3 Display Update
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
main microcontroller interfaces to it via the data bus at
addresses 0FFF8H, 0FFF9H, 0FFFAH, 0FFFBH.
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MTA7912 Service Manual Theory of Operation
• The patient display is driven by driver chip U6. The
main 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 main microcontroller interfaces to it via the
data bus at addresses 0FFECH, 0FFEDH, 0FFEEH,
0FFEFH.
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 main
microcontroller and the ALERT, ADD WATER, CHECK
PATIENT, CHECK FLOW, REMOVE FROM USE
NOW, and SELECT drivers via the data bus at address
0FFBFH. A high signal written to the latch by the main
microcontroller activates the individual inverter/drivers
to light the corresponding indicator.
• The mode display latch U54 is the interface between
main microcontroller and the FLOW-OK, COOLING,
WARMING, PATIENT CONTROL, BLANKET
CONTROL, and MONITOR ONLY drivers via the data
bus at address 0FFDFH. A high signal written to the
latch by the main 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
main 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 located on the alarm/backup board is driven
by a high signal from the control latch U51 (from the main
microcontroller via the data bus at address 0FF7FH) or a high
RFU IN signal from Q10 on the power supply board or a high
signal from the PIC microcontroller on the alarm/backup board. A
low data line signal from the main microcontroller to U51 causes a
high signal on the latch output. Therefore, the alarm is “active low”
in the eyes of the main microcontroller. NOR gate U40, driver U26
and transistor Q1 work in conjunction to activate the alarm.
6.4.4 Peripheral Input
The input buffer U55 is the interface between the main
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. Pressing this switch while
powering up the machine will cause the machine to execute code
which implements several service modes for troubleshooting use.
6.4.5 Water/Patient Temperature Control
If the machine is in BLANKET CONTROL mode, the water
temperature as sensed by the water temperature probe is used
as the feedback signal for controlling the water temperature to the
BLANKET CONTROL mode set point temperature.
If the machine is in PATIENT CONTROL 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 PATIENT CONTROL mode set
point temperature. The machine accomplishes this by adjusting
the water temperature. The water temperature the machine uses
in PATIENT CONTROL 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. This may not be the most comfortable setting for the
patient.
MODERATE - Water temperature is limted to 15°C below the
patient’s temperature. This will provide an improved comfort
setting to the patient.
GRADUAL - Water temperature is limited to 10°C 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 41°C. This is the fastest warming mode
the machine can provide.
MODERATE - The patient temperature will increase at a rate
of 1°C in a period of 3 hours (0.33°C/Hr).
GRADUAL - The patient temperature will increase at a rate
of 1°C in a period of 6 hours (0.17°C/Hr).
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MTA7912 Service Manual
When WARMING a patient in MODERATE or GRADUAL modes,
water temperatue is limited to a maximum of 41.0°C and a
minimum which is determined by the current CONTROL OPTION
selected (15°C below the patient temperature in MODERATE
mode an 10°C below the patient temperature in GRADUAL
mode).
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.
If the patient temperature deviates from the warming rate
specied by the CONTROL OPTION selected (MODERATE or
GRADUAL only) by 1.0°C, 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 of the
warming rate specied by the CONTROL OPTION selected,
the PATIENT temerature and ALERT light will stop ashing
and the audible alarm will silence.
NOTE: If the control MODE or SETPOINT 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 interrupted. 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 main microcontroller 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 main microcontroller. 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
PATIENT CONTROL or BLANKET CONTROL modes.
The control latch U51 on the control/display board is the interface
between the main microcontroller (via the data bus at address
0FF7FH) and the peripheral drivers on the power supply board.
Interface circuitry on the power supply board consists of U1, U2,
U7, U8, Q3, Q4, Q8, Q9, and associated components. U1, U2,
U7, and U8 are optically coupled triac drivers used to control
their respective triacs (Q3, Q4, Q8, and Q9); these combinations
provide electrical isolation between the low voltage main
microcontroller control circuits and the line voltage circuits.
The heater, pump, hot solenoid valve, and cold solenoid valve
are individually controlled by the main microcontroller through
latch U51 on the control/display board. A high signal on the data
line from the main microcontroller causes a low signal on the
appropriate output line of U51 which then sinks current from the
power supply board to activate the peripheral devices.
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.
6.4.6 Cold Water Reservoir Temperature Control
The control latch U51 on the control/display board is the interface
between the main microcontroller (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 main microcontroller switches power through the relay
to the refrigeration compressor at cut-out and cut-in temperatures
of 3.3°C and 5.8°C. These temperatures are sensed by the cold
water reservoir probe RTl located in the water reservoir. (See
gure 16, p. 55.) Control of the cold water reservoir temperature
takes place whenever the machine is on.
6.4.7 Backup Water Temperature Limiting
Water temperature limiting is provided by two systems; Backup
System I and Backup System II.
Backup System I consists of a PIC microcontroller residing on the
alarm/backup board, the over-temperature probe RT3 located in
the base, and one of the REMOVE FROM USE NOW latching
circuits on the power supply board.
Backup System II consists of two REMOVE FROM USE NOW
latching circuits and two xed non-adjustable temperature limit
thermostats, S1 and S2 located in the base.
6.4.7.1 REMOVE FROM USE NOW Latching Circuits
The power supply board includes two REMOVE FROM USE
NOW latching circuits made up of U3, U4, U5, U6, U9, U10, D2,
D3, Q1, Q2, and their interconnecting components. 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.
6.4.7.2 Backup System I
The PIC microcontroller has its own power supply on the alarm/
backup board which is independent of the main microcontroller’s
Theory of Operation
14

MTA7912 Service Manual
power supply circuits. Transformer T1 output is rectied and
ltered to generate unregulated positive voltage. Q1 is a linear
regulator with a nominal output of +5.0 volts. Interface circuitry
for Backup System 1 consists of Q2 and R1 on the alarm/backup
board and optical coupler U4 on the power supply board which is
powered by the independent power supply of the alarm/backup
board.
The PIC microcontroller repetitively compares the resistance of
the RT3 over-temperature probe (which is a 400 series thermistor
in the water ow path) with xed precision resistor R11. When the
water temperature (as sensed by RT3) surpasses the temperature
represented by the xed resistor (see section 3.2, Thermal
Specications, page 3, for the RT3 high temperature limit) the PIC
commands a REMOVE FROM USE NOW shutdown condition
via optical coupler U4 on the power supply board. It also signals
the audible alarm directly with a continuous tone (regardless of
the main microcontroller operational status). These commanded
signals by the PIC microcontroller will remain until the machine is
powered down.
U4 prevents Q1 from turning on so 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 PIC command signal is removed. The
output of either U9 or U10, through buffer Q10, signals the main
microcontroller that a REMOVE FROM USE NOW condition has
resulted. Thus, should the PIC microcontroller sense an over
temperature condition, the heater and pump are shut off and the
main microcontroller is notied.
6.4.7.3 Backup System II
If the water falls into the low temperature limit range, S1 will open.
If the water temperature rises into the high temperature range, S2
will open (see section 3.2, ThermalSpecications, page 3, for the
high and low temperature limits).
When either 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 main microcontroller that a REMOVE FROM USE
NOW condition has resulted. Thus, should either thermostat
(S1 or S2) trip, the heater and pump are shut off and the main
microcontroller is notied.
6.4.7.4 Both Backup System I and II
On the control/display board, a high signal from Q10 of the power
supply boards feed drivers U52 to light the REMOVE FROM
USE NOW LED, feeds driver U11 to light the ALERT LED, and
feeds NOR gate U40 to drive the audible alarm located on the
alarm/backup board. All this is done independent of the main
microcontroller. The same signal is sent to port P3.2 of the
microcontroller through C1, R1, and driver U11.
6.4.7.5 If The Main Microcontroller Is Nonoperational
If the main microcontroller is nonoperational at the event of a
signal from Q10 of the power supply board, the user is notied
of the REMOVE FROM USE NOW condition by the fact that all
the above mentioned indicators are on continuously. In addition,
the separate redundant circuits on the power supply board, each
triggered by either of the thermostats, or one triggered by the
PIC microcontroller, insure that the pump and heater remain off
even if the thermostat closes again or the PIC command signal is
lost. The REMOVE FROM USE NOW condition remains latched
and can be cleared only by an operator intervention in the form
of turning the machine circuit breaker off. If upon machine turn
on the fault condition still exists, the REMOVE FROM USE NOW
condition will recur.
6.4.7.6 If the Main Microcontroller is Operational
If the main microcontroller is operational at the event of a high
signal from Q10 of the power supply board (originating from
BACKUP SYSTEM I or BACKUP SYSTEM II), the signal at
P3.2 causes the main microcontroller to shut off the 7 segment
displays, ash the ALERT LED and light the REMOVE FROM
USE NOW LED, toggle the audible alarm, store the appropriate
RFU (Remove From Use) 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. (Separate machine service modes allow for
viewing the RFU code and for debugging problems. See section
8.0.)
The process of turning off the heater and pump triacs Q3 and Q4
by the main microcontroller removes power from the REMOVE
FROM USE NOW circuitry on the power board which then allows
the indicators on the control/display board to toggle under main
microcontroller control.
Note: The audible alarm will be a continuous tone
for an over temperature condition sensed by
BACKUP SYSTEM 1 regardless of the operational
status of the main microcontroller since the PIC
microcontroller puts out a continuous signal to the
audible independently which does not get reset
and which overrides any pulsing of the audible the
main microcontroller may perform.
The shutdown condition by the main microcontroller program will
remain until the machine is powered down. If, upon machine turn
on, the fault condition still exists, power replaced to the REMOVE
FROM USE NOW circuits on the power supply board when a
Theory of Operation
15

MTA7912 Service ManualTheory of Operation
mode is selected (or automatically every 60 seconds in standby
mode) will cause the REMOVE FROM USE NOW condition to
recur.
6.4.7.7 Other REMOVE FROM USE NOW Shutdown
Conditions
If during normal operation the main microcontroller senses
internal problems, it will cause a machine shutdown condition
as in 6.4.7.6. As a precaution, it also sends an output signal
from port pin P3.4 through U40 on the control/display board,
to command, via Q11 and U6 on the power supply board a
REMOVE FROM USE NOW shutdown condition of the latches.
The appropriate RFU (Remove From Use) code for the shutdown
will be stored. See section 8.0.
6.4.8 Power Loss
The PIC microcontroller also provides the POWER LOSS
detection function. The Q1 linear regulator is provided voltage
also from an 8.4V nominal nickel metal hydride battery when the
auxiliary switch of the circuit breaker CB1 is closed (indicating the
circuit breaker is in the on position) and the main microcontroller
power supply circuits are not powered. The PIC microcontroller
detects this POWER LOSS condition via the optical coupler U3
which is tied to the main microcontroller power supply circuits.
6.4.9 Battery Charging
When the main microcontroller power supply circuits are powered
and the auxiliary switch of the circuit breaker CB1 is closed
(indicating the circuit breaker is in the on position), the battery is
trickle charged through R3 on the alarm/backup board.
6.4.10 Detection of Operational Backup System 1
The PIC microcontroller provides the 1 second power-up tone
for the machine. This can be used by the user to ascertain
whether the PIC microcontroller is operational. But, whenever the
machine is on the PIC microcontroller also creates a 0.15 second
on, 0.15 second off square wave pulse which is fed to the main
microcontroller via optical coupler U4 on the alarm/backup board.
The main microcontroller constantly monitors for this signal via the
CONN_SENSE line. If the pulse is not there or if it is not if it is
not correct, the main microcontroller shuts the machine down with
a REMOVE FROM USE NOW condition because this indicates
that the alarm/backup board has either been disconnected or the
PIC is not operational.
16

MTA7912 Service Manual
7.0 Functional Check, Safety Inspection, and
Preventive Maintenance
7.1 Receiving Inspection Procedures
CONCEALED DAMAGE
After unpacking the Medi-Therm III machine, inspect the machine
for concealed damage. Save all packing material and carefully
describe or photograph the damage. Notify the carrier at once and
ask for an inspection (in writing). Failure to do this within 15 days
may result in loss of claim.
Before placing the Medi-Therm III machine into service, remove
the three compressor shipping braces (see p. 74, g. B), attach
the power cord (p. 59), ll the reservoir with distilled water (p.
3 and p. 7), make sure the power loss indication works ((e), p.
19), and perform a Functional Check and Safety Inspection (pp.
18-22).
7.2 Cleaning and Storage Procedures
FLUID SYSTEM
Use distilled water to retard algae growth and mineral buildup.
Change the distilled water monthly or more often depending upon
use.
The water circulation system, including reusable blankets, should
be cleaned every month to retard algae growth.
To clean the uid system, drain the machine and prepare an
algaecidal solution according to manufacturer’s instructions.
Use AirKem A-33 or equivalent. Add the solution to the machine,
attach blankets, set the machine in BLANKET CONTROL mode
to a setpoint temperature of 27°C and circulate the solution for
12 hours. Drain the solution and rell the machine with distilled
water. Algaecide solution may be readded to the water and left in
the machine in the recommended concentration to further retard
algae growth.
• Do not exceed proper algaecidal solution concentration.
Excessive algaecide may cause foaming, which can
damage the circulating pump.
• Do not use bleach (sodium hypochlorite). Bleach will
damage the heating element in the machine, which
could result in excessive leakage current.
COMPRESSOR
Dirt that has accumulated on the condenser coils and cooling ns
within the machine will reduce the efciency of the compressor
and should be removed with a vacuum cleaner or compressed air
hose. This will require removal of the rear bafe assembly. This
should be checked monthly or more frequently depending upon
use. See gure 18, p. 57.
CAUTION
PUMP
Pump motor should be oiled once a year with 3-4 drops of general
purpose motor oil in the locations identied on the pump label.
7.2.1 Machine Cleaning
Users should not use cleaning or decontamination
methods different from those recommended.
To clean the external surfaces of the machine and connector
hose, use a nonabrasive cleaning solution (such as warm, soapy
water) and a clean cloth. Wipe or air dry. Apply a disinfectant
such as 10% chlorinated bleach solution (chlorinated bleach with
5.25% sodium hypochlorite) to the external surfaces and allow to
dry.
Do not use bleach within the machine.
7.2.2 Reusable Blanket Care
• Do not store lled blankets. Algae growth may occur
inside.
• Do not use a blanket if severe algae buildup occurs.
• Do not expose blankets to temperatures over 65°C.
REUSABLE BLANKETS
To clean inside reusable blankets, attach the blankets to the
machine and follow instructions for section 7.2, Cleaning and
Storage Procedures, Fluid System.
To clean the outside of a reusable blanket:
1. Manually clean both sides of the blanket on a at surface
with warm water, a mild commercial detergent, and a sponge
or cloth.
2. Thoroughly rinse with clean water for 30 seconds.
3. Air dry or wipe with a clean cloth.
4. Apply a disinfectant such as a 10% chlorinated bleach
solution (chlorinated bleach with 5.25% sodium hypochlorite)
to both sides of the blanket.
5. Allow to air dry. Solution contact time is what makes
disinfection effective.
NOTE: Excess solution pooled in the buttons can be
removed with a clean, dry cloth.
CAUTION
Functional Check, Safety Inspection, and Maintenance
17
CAUTION